diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,27 @@
+## Fourmolu 0.15.0.0
+
+* Add `single-deriving-parens` configuration option to determine if `deriving` clauses of a single type should be parenthesized ([#386](https://github.com/fourmolu/fourmolu/pull/386))
+
+* Fix the order in which the configurations are applied ([#390](https://github.com/fourmolu/fourmolu/issues/390))
+
+### Upstream changes:
+
+#### Ormolu 0.7.4.0
+
+* Don't error when the `JavaScriptFFI` language pragma is present. [Issue
+  1087](https://github.com/tweag/ormolu/issues/1087).
+* Improve comment placement in if-then-else blocks. [Issue
+  998](https://github.com/tweag/ormolu/issues/998).
+* Now command line options for fixity overrides and module re-exports
+  overwrite information from `.ormolu` files. [Issue
+  1030](https://github.com/tweag/ormolu/issues/1030).
+* Respect newlines in data declarations in more cases. [Issue
+  1077](https://github.com/tweag/ormolu/issues/1077) and [issue
+  947](https://github.com/tweag/ormolu/issues/947).
+* The `-d / --debug` command line option now makes Ormolu print out debug
+  information regarding operator fixity inference. [Issue
+  1060](https://github.com/tweag/ormolu/issues/1060).
+
 ## Fourmolu 0.14.1.0
 
 * Fix `single-constraint-parens: never` for nested quantified constraints ([#374](https://github.com/fourmolu/fourmolu/issues/374))
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -15,6 +15,8 @@
     * [Regions](#regions)
     * [Exit codes](#exit-codes)
     * [Using as a library](#using-as-a-library)
+* [Troubleshooting](#troubleshooting)
+    * [Operators are being formatted weirdly!](#operators-are-being-formatted-weirdly)
 * [Limitations](#limitations)
 * [Contributing](#contributing)
 * [License](#license)
@@ -229,6 +231,32 @@
 For these purposes only the top `Ormolu` module should be considered stable.
 It follows [PVP](https://pvp.haskell.org/) starting from the version
 0.10.2.0. Rely on other modules at your own risk.
+
+## Troubleshooting
+
+### Operators are being formatted weirdly!
+
+This can happen when Ormolu doesn't know or can't determine the fixity of an
+operator.
+
+* If this is a custom operator, see the instructions in the [Language
+  extensions, dependencies, and
+  fixities](#language-extensions-dependencies-and-fixities) section to
+  specify the correct fixities in a `.ormolu` file.
+
+* If this is a third-party operator (e.g. from `base` or some other package
+  from Hackage), Ormolu probably doesn't recognize that the operator is the
+  same as the third-party one.
+
+  Some reasons this might be the case:
+
+    * You might have a custom Prelude that re-exports things from Prelude
+    * You might have `-XNoImplicitPrelude` turned on
+
+  If any of these are true, make sure to specify the reexports correctly in
+  a `.ormolu` file.
+
+You can see how Ormolu decides the fixity of operators if you use `--debug`.
 
 ## Limitations
 
diff --git a/app/Main.hs b/app/Main.hs
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -100,8 +100,8 @@
     cliConfig
       { cfgPrinterOpts =
           resolvePrinterOpts
-            [ cliPrinterOpts,
-              cfgFilePrinterOpts fourmoluConfig
+            [ cfgFilePrinterOpts fourmoluConfig,
+              cliPrinterOpts
             ],
         cfgFixityOverrides =
           FixityOverrides . mconcat . map unFixityOverrides $
@@ -242,15 +242,17 @@
             fromMaybe
               ModuleSource
               (reqSourceType <|> mdetectedSourceType)
-      let mfixityOverrides = fst <$> mdotOrmolu
-          mmoduleReexports = snd <$> mdotOrmolu
       return $
         refineConfig
           sourceType
           mcabalInfo
-          mfixityOverrides
-          mmoduleReexports
-          rawConfig
+          (Just (cfgFixityOverrides rawConfig))
+          (Just (cfgModuleReexports rawConfig))
+          ( rawConfig
+              { cfgFixityOverrides = maybe defaultFixityOverrides fst mdotOrmolu,
+                cfgModuleReexports = maybe defaultModuleReexports snd mdotOrmolu
+              }
+          )
     handleDiff originalInput formattedInput fileRepr =
       case diffText originalInput formattedInput fileRepr of
         Nothing -> return ExitSuccess
diff --git a/data/examples/declaration/data/ctype-0-four-out.hs b/data/examples/declaration/data/ctype-0-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/ctype-0-four-out.hs
@@ -0,0 +1,1 @@
+data {-# CTYPE "unistd.h" "useconds_t" #-} T
diff --git a/data/examples/declaration/data/ctype-0-out.hs b/data/examples/declaration/data/ctype-0-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/ctype-0-out.hs
@@ -0,0 +1,1 @@
+data {-# CTYPE "unistd.h" "useconds_t" #-} T
diff --git a/data/examples/declaration/data/ctype-0.hs b/data/examples/declaration/data/ctype-0.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/ctype-0.hs
@@ -0,0 +1,1 @@
+data    {-# CTYPE "unistd.h" "useconds_t" #-} T
diff --git a/data/examples/declaration/data/ctype-1-four-out.hs b/data/examples/declaration/data/ctype-1-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/ctype-1-four-out.hs
@@ -0,0 +1,6 @@
+data
+    {-# CTYPE "header.h" "an-ffi-type-with-along-name" #-}
+    AnFFITypeWithAlongName = AnFFITypeWithAlongName
+    { a :: X
+    , b :: Y
+    }
diff --git a/data/examples/declaration/data/ctype-1-out.hs b/data/examples/declaration/data/ctype-1-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/ctype-1-out.hs
@@ -0,0 +1,6 @@
+data
+  {-# CTYPE "header.h" "an-ffi-type-with-along-name" #-}
+  AnFFITypeWithAlongName = AnFFITypeWithAlongName
+  { a :: X,
+    b :: Y
+  }
diff --git a/data/examples/declaration/data/ctype-1.hs b/data/examples/declaration/data/ctype-1.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/ctype-1.hs
@@ -0,0 +1,6 @@
+data
+  {-# CTYPE "header.h" "an-ffi-type-with-along-name"  #-}
+  AnFFITypeWithAlongName = AnFFITypeWithAlongName
+  { a :: X,
+    b :: Y
+  }
diff --git a/data/examples/declaration/data/ctype-four-out.hs b/data/examples/declaration/data/ctype-four-out.hs
deleted file mode 100644
--- a/data/examples/declaration/data/ctype-four-out.hs
+++ /dev/null
@@ -1,1 +0,0 @@
-data {-# CTYPE "unistd.h" "useconds_t" #-} T
diff --git a/data/examples/declaration/data/ctype-out.hs b/data/examples/declaration/data/ctype-out.hs
deleted file mode 100644
--- a/data/examples/declaration/data/ctype-out.hs
+++ /dev/null
@@ -1,1 +0,0 @@
-data {-# CTYPE "unistd.h" "useconds_t" #-} T
diff --git a/data/examples/declaration/data/ctype.hs b/data/examples/declaration/data/ctype.hs
deleted file mode 100644
--- a/data/examples/declaration/data/ctype.hs
+++ /dev/null
@@ -1,1 +0,0 @@
-data    {-# CTYPE "unistd.h" "useconds_t" #-} T
diff --git a/data/examples/declaration/data/field-layout/record-0-four-out.hs b/data/examples/declaration/data/field-layout/record-0-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-0-four-out.hs
@@ -0,0 +1,10 @@
+-- | Foo.
+data Foo = Foo
+    { foo :: Foo Int Int
+    -- ^ Something
+    , bar ::
+        Bar
+            Char
+            Char
+    -- ^ Something else
+    }
diff --git a/data/examples/declaration/data/field-layout/record-0-out.hs b/data/examples/declaration/data/field-layout/record-0-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-0-out.hs
@@ -0,0 +1,10 @@
+-- | Foo.
+data Foo = Foo
+  { -- | Something
+    foo :: Foo Int Int,
+    -- | Something else
+    bar ::
+      Bar
+        Char
+        Char
+  }
diff --git a/data/examples/declaration/data/field-layout/record-0.hs b/data/examples/declaration/data/field-layout/record-0.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-0.hs
@@ -0,0 +1,9 @@
+-- | Foo.
+
+data Foo = Foo
+  { foo :: Foo Int Int
+    -- ^ Something
+  , bar :: Bar Char
+           Char
+    -- ^ Something else
+  }
diff --git a/data/examples/declaration/data/field-layout/record-1-four-out.hs b/data/examples/declaration/data/field-layout/record-1-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-1-four-out.hs
@@ -0,0 +1,11 @@
+-- | Foo.
+data Foo
+    = Foo
+    { foo :: Foo Int Int
+    -- ^ Something
+    , bar ::
+        Bar
+            Char
+            Char
+    -- ^ Something else
+    }
diff --git a/data/examples/declaration/data/field-layout/record-1-out.hs b/data/examples/declaration/data/field-layout/record-1-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-1-out.hs
@@ -0,0 +1,11 @@
+-- | Foo.
+data Foo
+  = Foo
+  { -- | Something
+    foo :: Foo Int Int,
+    -- | Something else
+    bar ::
+      Bar
+        Char
+        Char
+  }
diff --git a/data/examples/declaration/data/field-layout/record-1.hs b/data/examples/declaration/data/field-layout/record-1.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-1.hs
@@ -0,0 +1,10 @@
+-- | Foo.
+
+data Foo =
+  Foo
+  { foo :: Foo Int Int
+    -- ^ Something
+  , bar :: Bar Char
+           Char
+    -- ^ Something else
+  }
diff --git a/data/examples/declaration/data/field-layout/record-2-four-out.hs b/data/examples/declaration/data/field-layout/record-2-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-2-four-out.hs
@@ -0,0 +1,7 @@
+data IndexWithInfo schema
+    = forall x.
+      IndexWithInfo
+    { checkedIndex :: Index schema x
+    , checkedIndexName :: U.Variable
+    , checkedIndexType :: Type x
+    }
diff --git a/data/examples/declaration/data/field-layout/record-2-out.hs b/data/examples/declaration/data/field-layout/record-2-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-2-out.hs
@@ -0,0 +1,7 @@
+data IndexWithInfo schema
+  = forall x.
+  IndexWithInfo
+  { checkedIndex :: Index schema x,
+    checkedIndexName :: U.Variable,
+    checkedIndexType :: Type x
+  }
diff --git a/data/examples/declaration/data/field-layout/record-2.hs b/data/examples/declaration/data/field-layout/record-2.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/field-layout/record-2.hs
@@ -0,0 +1,7 @@
+data IndexWithInfo schema =
+  forall x.
+  IndexWithInfo
+    { checkedIndex :: Index schema x
+    , checkedIndexName :: U.Variable
+    , checkedIndexType :: Type x
+    }
diff --git a/data/examples/declaration/data/field-layout/record-four-out.hs b/data/examples/declaration/data/field-layout/record-four-out.hs
deleted file mode 100644
--- a/data/examples/declaration/data/field-layout/record-four-out.hs
+++ /dev/null
@@ -1,12 +0,0 @@
-module Main where
-
--- | Foo.
-data Foo = Foo
-    { foo :: Foo Int Int
-    -- ^ Something
-    , bar ::
-        Bar
-            Char
-            Char
-    -- ^ Something else
-    }
diff --git a/data/examples/declaration/data/field-layout/record-out.hs b/data/examples/declaration/data/field-layout/record-out.hs
deleted file mode 100644
--- a/data/examples/declaration/data/field-layout/record-out.hs
+++ /dev/null
@@ -1,12 +0,0 @@
-module Main where
-
--- | Foo.
-data Foo = Foo
-  { -- | Something
-    foo :: Foo Int Int,
-    -- | Something else
-    bar ::
-      Bar
-        Char
-        Char
-  }
diff --git a/data/examples/declaration/data/field-layout/record.hs b/data/examples/declaration/data/field-layout/record.hs
deleted file mode 100644
--- a/data/examples/declaration/data/field-layout/record.hs
+++ /dev/null
@@ -1,11 +0,0 @@
-module Main where
-
--- | Foo.
-
-data Foo = Foo
-  { foo :: Foo Int Int
-    -- ^ Something
-  , bar :: Bar Char
-           Char
-    -- ^ Something else
-  }
diff --git a/data/examples/declaration/data/record-fancy-existential-four-out.hs b/data/examples/declaration/data/record-fancy-existential-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/record-fancy-existential-four-out.hs
@@ -0,0 +1,6 @@
+{-# LANGUAGE ExistentialQuantification #-}
+
+data Foo = forall a b. (Show a, Eq b) => Bar
+    { foo :: a
+    , bars :: b
+    }
diff --git a/data/examples/declaration/data/record-fancy-existential-out.hs b/data/examples/declaration/data/record-fancy-existential-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/record-fancy-existential-out.hs
@@ -0,0 +1,6 @@
+{-# LANGUAGE ExistentialQuantification #-}
+
+data Foo = forall a b. (Show a, Eq b) => Bar
+  { foo :: a,
+    bars :: b
+  }
diff --git a/data/examples/declaration/data/record-fancy-existential.hs b/data/examples/declaration/data/record-fancy-existential.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/data/record-fancy-existential.hs
@@ -0,0 +1,5 @@
+{-# LANGUAGE ExistentialQuantification #-}
+data Foo = forall a b . (Show a, Eq b) => Bar
+  { foo  :: a
+  , bars :: b
+  }
diff --git a/data/examples/declaration/data/simple-broken-four-out.hs b/data/examples/declaration/data/simple-broken-four-out.hs
--- a/data/examples/declaration/data/simple-broken-four-out.hs
+++ b/data/examples/declaration/data/simple-broken-four-out.hs
@@ -1,7 +1,8 @@
 module Main where
 
 -- | Here we go.
-data Foo = Foo {unFoo :: Int}
+data Foo
+    = Foo {unFoo :: Int}
     deriving (Eq)
 
 -- | And once again.
diff --git a/data/examples/declaration/data/simple-broken-out.hs b/data/examples/declaration/data/simple-broken-out.hs
--- a/data/examples/declaration/data/simple-broken-out.hs
+++ b/data/examples/declaration/data/simple-broken-out.hs
@@ -1,7 +1,8 @@
 module Main where
 
 -- | Here we go.
-data Foo = Foo {unFoo :: Int}
+data Foo
+  = Foo {unFoo :: Int}
   deriving (Eq)
 
 -- | And once again.
diff --git a/data/examples/declaration/value/function/if-single-line-functions-do-four-out.hs b/data/examples/declaration/value/function/if-single-line-functions-do-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-single-line-functions-do-four-out.hs
@@ -0,0 +1,5 @@
+foo x = do
+    y <- quux
+    if x > 2
+        then bar x
+        else baz y
diff --git a/data/examples/declaration/value/function/if-single-line-functions-do-out.hs b/data/examples/declaration/value/function/if-single-line-functions-do-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-single-line-functions-do-out.hs
@@ -0,0 +1,5 @@
+foo x = do
+  y <- quux
+  if x > 2
+    then bar x
+    else baz y
diff --git a/data/examples/declaration/value/function/if-single-line-functions-do.hs b/data/examples/declaration/value/function/if-single-line-functions-do.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-single-line-functions-do.hs
@@ -0,0 +1,5 @@
+foo x = do
+  y <- quux
+  if x > 2
+    then bar x
+    else baz y
diff --git a/data/examples/declaration/value/function/if-single-line-functions-four-out.hs b/data/examples/declaration/value/function/if-single-line-functions-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-single-line-functions-four-out.hs
@@ -0,0 +1,4 @@
+foo x =
+    if x > 2
+        then bar x
+        else baz x
diff --git a/data/examples/declaration/value/function/if-single-line-functions-out.hs b/data/examples/declaration/value/function/if-single-line-functions-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-single-line-functions-out.hs
@@ -0,0 +1,4 @@
+foo x =
+  if x > 2
+    then bar x
+    else baz x
diff --git a/data/examples/declaration/value/function/if-single-line-functions.hs b/data/examples/declaration/value/function/if-single-line-functions.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-single-line-functions.hs
@@ -0,0 +1,4 @@
+foo x =
+  if x > 2
+    then bar x
+    else baz x
diff --git a/data/examples/declaration/value/function/if-with-comment-above-branches-four-out.hs b/data/examples/declaration/value/function/if-with-comment-above-branches-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-above-branches-four-out.hs
@@ -0,0 +1,7 @@
+foo =
+    if undefined
+        -- then comment
+        then undefined
+        -- else comment
+        else do
+            undefined
diff --git a/data/examples/declaration/value/function/if-with-comment-above-branches-out.hs b/data/examples/declaration/value/function/if-with-comment-above-branches-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-above-branches-out.hs
@@ -0,0 +1,7 @@
+foo =
+  if undefined
+    -- then comment
+    then undefined
+    -- else comment
+    else do
+      undefined
diff --git a/data/examples/declaration/value/function/if-with-comment-above-branches.hs b/data/examples/declaration/value/function/if-with-comment-above-branches.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-above-branches.hs
@@ -0,0 +1,8 @@
+foo =
+  if undefined
+    -- then comment
+    then undefined
+    -- else comment
+    else
+      do
+        undefined
diff --git a/data/examples/declaration/value/function/if-with-comment-before-do-blocks-four-out.hs b/data/examples/declaration/value/function/if-with-comment-before-do-blocks-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-before-do-blocks-four-out.hs
@@ -0,0 +1,10 @@
+foo =
+    if something
+        -- then comment
+        then do
+            stuff
+            stuff
+        -- else comment
+        else do
+            stuff
+            stuff
diff --git a/data/examples/declaration/value/function/if-with-comment-before-do-blocks-out.hs b/data/examples/declaration/value/function/if-with-comment-before-do-blocks-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-before-do-blocks-out.hs
@@ -0,0 +1,10 @@
+foo =
+  if something
+    -- then comment
+    then do
+      stuff
+      stuff
+    -- else comment
+    else do
+      stuff
+      stuff
diff --git a/data/examples/declaration/value/function/if-with-comment-before-do-blocks.hs b/data/examples/declaration/value/function/if-with-comment-before-do-blocks.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-before-do-blocks.hs
@@ -0,0 +1,10 @@
+foo =
+  if something
+    -- then comment
+    then do
+      stuff
+      stuff
+    -- else comment
+    else do
+      stuff
+      stuff
diff --git a/data/examples/declaration/value/function/if-with-comment-four-out.hs b/data/examples/declaration/value/function/if-with-comment-four-out.hs
deleted file mode 100644
--- a/data/examples/declaration/value/function/if-with-comment-four-out.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-foo =
-    if undefined
-        then -- then comment
-            undefined
-        else -- else comment
-
-        do
-            undefined
diff --git a/data/examples/declaration/value/function/if-with-comment-in-branches-four-out.hs b/data/examples/declaration/value/function/if-with-comment-in-branches-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-in-branches-four-out.hs
@@ -0,0 +1,14 @@
+foo =
+    if x
+        then
+            -- comment 1
+            -- comment 2
+            case a of
+                Just b -> _
+                Nothing -> _
+        else
+            -- comment 3
+            -- comment 4
+            case a of
+                Just b -> _
+                Nothing -> _
diff --git a/data/examples/declaration/value/function/if-with-comment-in-branches-out.hs b/data/examples/declaration/value/function/if-with-comment-in-branches-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-in-branches-out.hs
@@ -0,0 +1,14 @@
+foo =
+  if x
+    then
+      -- comment 1
+      -- comment 2
+      case a of
+        Just b -> _
+        Nothing -> _
+    else
+      -- comment 3
+      -- comment 4
+      case a of
+        Just b -> _
+        Nothing -> _
diff --git a/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions-four-out.hs b/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions-four-out.hs
@@ -0,0 +1,12 @@
+foo =
+    if x
+        then
+            -- comment 1
+            -- comment 2
+            foo 1 2 3
+        else
+            -- comment 3
+            -- comment 4
+            foo
+                "here"
+                "there"
diff --git a/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions-out.hs b/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions-out.hs
@@ -0,0 +1,12 @@
+foo =
+  if x
+    then
+      -- comment 1
+      -- comment 2
+      foo 1 2 3
+    else
+      -- comment 3
+      -- comment 4
+      foo
+        "here"
+        "there"
diff --git a/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions.hs b/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-in-branches-with-functions.hs
@@ -0,0 +1,12 @@
+foo =
+  if x
+    then
+      -- comment 1
+      -- comment 2
+      foo 1 2 3
+    else
+      -- comment 3
+      -- comment 4
+      foo
+        "here"
+        "there"
diff --git a/data/examples/declaration/value/function/if-with-comment-in-branches.hs b/data/examples/declaration/value/function/if-with-comment-in-branches.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-in-branches.hs
@@ -0,0 +1,14 @@
+foo =
+  if x
+    then
+      -- comment 1
+      -- comment 2
+      case a of
+        Just b -> _
+        Nothing -> _
+    else
+      -- comment 3
+      -- comment 4
+      case a of
+        Just b -> _
+        Nothing -> _
diff --git a/data/examples/declaration/value/function/if-with-comment-next-to-keyword-four-out.hs b/data/examples/declaration/value/function/if-with-comment-next-to-keyword-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-next-to-keyword-four-out.hs
@@ -0,0 +1,10 @@
+foo =
+    if x
+        then -- comment 1
+        -- comment 2
+            foo 1 2 3
+        else -- comment 3
+        -- comment 4
+            foo
+                "here"
+                "there"
diff --git a/data/examples/declaration/value/function/if-with-comment-next-to-keyword-out.hs b/data/examples/declaration/value/function/if-with-comment-next-to-keyword-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-next-to-keyword-out.hs
@@ -0,0 +1,10 @@
+foo =
+  if x
+    then -- comment 1
+    -- comment 2
+      foo 1 2 3
+    else -- comment 3
+    -- comment 4
+      foo
+        "here"
+        "there"
diff --git a/data/examples/declaration/value/function/if-with-comment-next-to-keyword.hs b/data/examples/declaration/value/function/if-with-comment-next-to-keyword.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/declaration/value/function/if-with-comment-next-to-keyword.hs
@@ -0,0 +1,10 @@
+foo =
+  if x
+    then -- comment 1
+      -- comment 2
+      foo 1 2 3
+    else -- comment 3
+      -- comment 4
+      foo
+        "here"
+        "there"
diff --git a/data/examples/declaration/value/function/if-with-comment-out.hs b/data/examples/declaration/value/function/if-with-comment-out.hs
deleted file mode 100644
--- a/data/examples/declaration/value/function/if-with-comment-out.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-foo =
-  if undefined
-    then -- then comment
-      undefined
-    else -- else comment
-
-    do
-      undefined
diff --git a/data/examples/declaration/value/function/if-with-comment.hs b/data/examples/declaration/value/function/if-with-comment.hs
deleted file mode 100644
--- a/data/examples/declaration/value/function/if-with-comment.hs
+++ /dev/null
@@ -1,8 +0,0 @@
-foo =
-  if undefined
-    -- then comment
-    then undefined
-    -- else comment
-    else
-      do
-        undefined
diff --git a/data/examples/other/jsffi-four-out.hs b/data/examples/other/jsffi-four-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/other/jsffi-four-out.hs
@@ -0,0 +1,1 @@
+{-# LANGUAGE JavaScriptFFI #-}
diff --git a/data/examples/other/jsffi-out.hs b/data/examples/other/jsffi-out.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/other/jsffi-out.hs
@@ -0,0 +1,1 @@
+{-# LANGUAGE JavaScriptFFI #-}
diff --git a/data/examples/other/jsffi.hs b/data/examples/other/jsffi.hs
new file mode 100644
--- /dev/null
+++ b/data/examples/other/jsffi.hs
@@ -0,0 +1,1 @@
+{-# language JavaScriptFFI #-}
diff --git a/data/fourmolu/single-deriving-parens/input.hs b/data/fourmolu/single-deriving-parens/input.hs
new file mode 100644
--- /dev/null
+++ b/data/fourmolu/single-deriving-parens/input.hs
@@ -0,0 +1,10 @@
+module Main where
+
+data Foo = Foo
+    deriving stock Show
+
+data Bar = Bar
+    deriving stock (Show, Eq)
+
+data Bat = Bat
+    deriving stock (Show)
diff --git a/data/fourmolu/single-deriving-parens/output-DerivingAlways.hs b/data/fourmolu/single-deriving-parens/output-DerivingAlways.hs
new file mode 100644
--- /dev/null
+++ b/data/fourmolu/single-deriving-parens/output-DerivingAlways.hs
@@ -0,0 +1,10 @@
+module Main where
+
+data Foo = Foo
+    deriving stock (Show)
+
+data Bar = Bar
+    deriving stock (Show, Eq)
+
+data Bat = Bat
+    deriving stock (Show)
diff --git a/data/fourmolu/single-deriving-parens/output-DerivingAuto.hs b/data/fourmolu/single-deriving-parens/output-DerivingAuto.hs
new file mode 100644
--- /dev/null
+++ b/data/fourmolu/single-deriving-parens/output-DerivingAuto.hs
@@ -0,0 +1,10 @@
+module Main where
+
+data Foo = Foo
+    deriving stock Show
+
+data Bar = Bar
+    deriving stock (Show, Eq)
+
+data Bat = Bat
+    deriving stock (Show)
diff --git a/data/fourmolu/single-deriving-parens/output-DerivingNever.hs b/data/fourmolu/single-deriving-parens/output-DerivingNever.hs
new file mode 100644
--- /dev/null
+++ b/data/fourmolu/single-deriving-parens/output-DerivingNever.hs
@@ -0,0 +1,10 @@
+module Main where
+
+data Foo = Foo
+    deriving stock Show
+
+data Bar = Bar
+    deriving stock (Show, Eq)
+
+data Bat = Bat
+    deriving stock Show
diff --git a/fixity-tests/test-0-no-extra-info-expected.hs b/fixity-tests/test-0-no-extra-info-expected.hs
deleted file mode 100644
--- a/fixity-tests/test-0-no-extra-info-expected.hs
+++ /dev/null
@@ -1,10 +0,0 @@
-instance A.ToJSON UpdateTable where
-  toJSON a =
-    A.object $
-      "TableName"
-        .= updateTableName a
-        :> "ProvisionedThroughput"
-        .= updateProvisionedThroughput a
-        :> case updateGlobalSecondaryIndexUpdates a of
-          [] -> []
-          l -> ["GlobalSecondaryIndexUpdates" .= l]
diff --git a/fixity-tests/test-0-ugly-expected.hs b/fixity-tests/test-0-ugly-expected.hs
new file mode 100644
--- /dev/null
+++ b/fixity-tests/test-0-ugly-expected.hs
@@ -0,0 +1,10 @@
+instance A.ToJSON UpdateTable where
+  toJSON a =
+    A.object $
+      "TableName"
+        .= updateTableName a
+        :> "ProvisionedThroughput"
+        .= updateProvisionedThroughput a
+        :> case updateGlobalSecondaryIndexUpdates a of
+          [] -> []
+          l -> ["GlobalSecondaryIndexUpdates" .= l]
diff --git a/fourmolu.cabal b/fourmolu.cabal
--- a/fourmolu.cabal
+++ b/fourmolu.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               fourmolu
-version:            0.14.1.0
+version:            0.15.0.0
 license:            BSD-3-Clause
 license-file:       LICENSE.md
 maintainer:
@@ -213,7 +213,7 @@
         Ormolu.Integration.Utils
     build-depends:
         bytestring,
-        Diff >=0.3 && <0.5,
+        Diff >=0.3 && <1,
         pretty >=1.0 && <2.0,
         process >=1.6 && <2.0,
         yaml,
diff --git a/fourmolu.yaml b/fourmolu.yaml
--- a/fourmolu.yaml
+++ b/fourmolu.yaml
@@ -14,6 +14,7 @@
 let-style: inline
 in-style: right-align
 single-constraint-parens: always
+single-deriving-parens: always
 unicode: never
 respectful: false
 fixities: []
diff --git a/src/GHC/DynFlags.hs b/src/GHC/DynFlags.hs
--- a/src/GHC/DynFlags.hs
+++ b/src/GHC/DynFlags.hs
@@ -26,7 +26,8 @@
         Platform
           { platformArchOS =
               ArchOS
-                { archOS_arch = ArchUnknown,
+                { -- see https://github.com/tweag/ormolu/issues/1087
+                  archOS_arch = ArchJavaScript,
                   archOS_OS = OSUnknown
                 },
             platformWordSize = PW8,
diff --git a/src/Ormolu.hs b/src/Ormolu.hs
--- a/src/Ormolu.hs
+++ b/src/Ormolu.hs
@@ -118,7 +118,7 @@
   -- when we try to parse the rendered code back, inside of GHC monad
   -- wrapper which will lead to error messages presenting the exceptions as
   -- GHC bugs.
-  let !formattedText = printSnippets result0 $ cfgPrinterOpts cfgWithIndices
+  let !formattedText = printSnippets (cfgDebug cfg) result0 $ cfgPrinterOpts cfgWithIndices
   when (not (cfgUnsafe cfg) || cfgCheckIdempotence cfg) $ do
     -- Parse the result of pretty-printing again and make sure that AST
     -- is the same as AST of original snippet module span positions.
@@ -144,7 +144,7 @@
     -- Try re-formatting the formatted result to check if we get exactly
     -- the same output.
     when (cfgCheckIdempotence cfg) . liftIO $
-      let reformattedText = printSnippets result1 $ cfgPrinterOpts cfgWithIndices
+      let reformattedText = printSnippets (cfgDebug cfg) result1 $ cfgPrinterOpts cfgWithIndices
        in case diffText formattedText reformattedText path of
             Nothing -> return ()
             Just diff -> throwIO (OrmoluNonIdempotentOutput diff)
diff --git a/src/Ormolu/Config.hs b/src/Ormolu/Config.hs
--- a/src/Ormolu/Config.hs
+++ b/src/Ormolu/Config.hs
@@ -42,6 +42,7 @@
     InStyle (..),
     Unicode (..),
     ColumnLimit (..),
+    SingleDerivingParens (..),
     parsePrinterOptsCLI,
     parsePrinterOptType,
 
@@ -58,6 +59,7 @@
 import Data.Aeson ((.!=), (.:?))
 import Data.Aeson qualified as Aeson
 import Data.Aeson.Types qualified as Aeson
+import Data.Foldable (foldl')
 import Data.Functor.Identity (Identity (..))
 import Data.Map.Strict qualified as Map
 import Data.Set (Set)
@@ -230,7 +232,7 @@
 
 -- | Apply the given configuration in order (later options override earlier).
 resolvePrinterOpts :: [PrinterOptsPartial] -> PrinterOptsTotal
-resolvePrinterOpts = foldr fillMissingPrinterOpts defaultPrinterOpts
+resolvePrinterOpts = foldl' (flip fillMissingPrinterOpts) defaultPrinterOpts
 
 ----------------------------------------------------------------------------
 -- Loading Fourmolu configuration
diff --git a/src/Ormolu/Config/Gen.hs b/src/Ormolu/Config/Gen.hs
--- a/src/Ormolu/Config/Gen.hs
+++ b/src/Ormolu/Config/Gen.hs
@@ -18,6 +18,7 @@
   , Unicode (..)
   , SingleConstraintParens (..)
   , ColumnLimit (..)
+  , SingleDerivingParens (..)
   , emptyPrinterOpts
   , defaultPrinterOpts
   , defaultPrinterOptsYaml
@@ -65,6 +66,8 @@
       poInStyle :: f InStyle
     , -- | Whether to put parentheses around a single constraint
       poSingleConstraintParens :: f SingleConstraintParens
+    , -- | Whether to put parentheses around a single deriving class
+      poSingleDerivingParens :: f SingleDerivingParens
     , -- | Output Unicode syntax
       poUnicode :: f Unicode
     , -- | Give the programmer more choice on where to insert blank lines
@@ -88,6 +91,7 @@
     , poLetStyle = Nothing
     , poInStyle = Nothing
     , poSingleConstraintParens = Nothing
+    , poSingleDerivingParens = Nothing
     , poUnicode = Nothing
     , poRespectful = Nothing
     }
@@ -108,6 +112,7 @@
     , poLetStyle = pure LetAuto
     , poInStyle = pure InRightAlign
     , poSingleConstraintParens = pure ConstraintAlways
+    , poSingleDerivingParens = pure DerivingAlways
     , poUnicode = pure UnicodeNever
     , poRespectful = pure True
     }
@@ -135,6 +140,7 @@
     , poLetStyle = maybe (poLetStyle p2) pure (poLetStyle p1)
     , poInStyle = maybe (poInStyle p2) pure (poInStyle p1)
     , poSingleConstraintParens = maybe (poSingleConstraintParens p2) pure (poSingleConstraintParens p1)
+    , poSingleDerivingParens = maybe (poSingleDerivingParens p2) pure (poSingleDerivingParens p1)
     , poUnicode = maybe (poUnicode p2) pure (poUnicode p1)
     , poRespectful = maybe (poRespectful p2) pure (poRespectful p1)
     }
@@ -198,6 +204,10 @@
       "Whether to put parentheses around a single constraint (choices: \"auto\", \"always\", or \"never\") (default: always)"
       "OPTION"
     <*> f
+      "single-deriving-parens"
+      "Whether to put parentheses around a single deriving class (choices: \"auto\", \"always\", or \"never\") (default: always)"
+      "OPTION"
+    <*> f
       "unicode"
       "Output Unicode syntax (choices: \"detect\", \"always\", or \"never\") (default: never)"
       "OPTION"
@@ -225,6 +235,7 @@
     <*> f "let-style"
     <*> f "in-style"
     <*> f "single-constraint-parens"
+    <*> f "single-deriving-parens"
     <*> f "unicode"
     <*> f "respectful"
 
@@ -305,6 +316,12 @@
   | ColumnLimit Int
   deriving (Eq, Show)
 
+data SingleDerivingParens
+  = DerivingAuto
+  | DerivingAlways
+  | DerivingNever
+  deriving (Eq, Show, Enum, Bounded)
+
 instance Aeson.FromJSON CommaStyle where
   parseJSON =
     Aeson.withText "CommaStyle" $ \s ->
@@ -490,6 +507,24 @@
               "Valid values are: \"none\", or an integer"
             ]
 
+instance Aeson.FromJSON SingleDerivingParens where
+  parseJSON =
+    Aeson.withText "SingleDerivingParens" $ \s ->
+      either Aeson.parseFail pure $
+        parsePrinterOptType (Text.unpack s)
+
+instance PrinterOptsFieldType SingleDerivingParens where
+  parsePrinterOptType s =
+    case s of
+      "auto" -> Right DerivingAuto
+      "always" -> Right DerivingAlways
+      "never" -> Right DerivingNever
+      _ ->
+        Left . unlines $
+          [ "unknown value: " <> show s
+          , "Valid values are: \"auto\", \"always\", or \"never\""
+          ]
+
 defaultPrinterOptsYaml :: String
 defaultPrinterOptsYaml =
   unlines
@@ -531,6 +566,9 @@
     , ""
     , "# Whether to put parentheses around a single constraint (choices: auto, always, or never)"
     , "single-constraint-parens: always"
+    , ""
+    , "# Whether to put parentheses around a single deriving class (choices: auto, always, or never)"
+    , "single-deriving-parens: always"
     , ""
     , "# Output Unicode syntax (choices: detect, always, or never)"
     , "unicode: never"
diff --git a/src/Ormolu/Diff/ParseResult.hs b/src/Ormolu/Diff/ParseResult.hs
--- a/src/Ormolu/Diff/ParseResult.hs
+++ b/src/Ormolu/Diff/ParseResult.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeepSubsumption #-}
+{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ViewPatterns #-}
 
@@ -160,5 +161,7 @@
     classDeclCtxEq tc tc' = genericQuery tc tc'
 
     derivedTyClsParensEq :: DerivClauseTys GhcPs -> GenericQ ParseResultDiff
-    derivedTyClsParensEq (DctSingle NoExtField sigTy) dct' = genericQuery (DctMulti NoExtField [sigTy]) dct'
-    derivedTyClsParensEq dct dct' = genericQuery dct dct'
+    derivedTyClsParensEq = considerEqualVia $ curry $ \case
+      (DctSingle _ ty, DctMulti _ [ty']) -> genericQuery ty ty'
+      (DctMulti _ [ty], DctSingle _ ty') -> genericQuery ty ty'
+      (x, y) -> genericQuery x y
diff --git a/src/Ormolu/Fixity/Internal.hs b/src/Ormolu/Fixity/Internal.hs
--- a/src/Ormolu/Fixity/Internal.hs
+++ b/src/Ormolu/Fixity/Internal.hs
@@ -42,6 +42,7 @@
 import Data.Text (Text)
 import Data.Text qualified as T
 import Data.Text.Encoding qualified as T
+import Debug.Trace (trace)
 import Distribution.ModuleName (ModuleName)
 import Distribution.Types.PackageName
 import GHC.Data.FastString (fs_sbs)
@@ -256,24 +257,62 @@
   deriving stock (Eq, Show)
 
 -- | Get a 'FixityApproximation' of an operator.
-inferFixity :: RdrName -> ModuleFixityMap -> FixityApproximation
-inferFixity rdrName (ModuleFixityMap m) =
-  case Map.lookup opName m of
-    Nothing -> defaultFixityApproximation
-    Just (Given fixityInfo) ->
-      fixityInfoToApproximation fixityInfo
-    Just (FromModuleImports xs) ->
-      let isMatching (provenance, _fixityInfo) =
-            case provenance of
-              UnqualifiedAndQualified mn ->
-                maybe True (== mn) moduleName
-              OnlyQualified mn ->
-                maybe False (== mn) moduleName
-       in fromMaybe defaultFixityApproximation
-            . foldMap (Just . fixityInfoToApproximation . snd)
-            $ NE.filter isMatching xs
+inferFixity ::
+  -- | Whether to print debug info regarding fixity inference
+  Bool ->
+  -- | Operator name
+  RdrName ->
+  -- | Module fixity map
+  ModuleFixityMap ->
+  -- | The resulting fixity approximation
+  FixityApproximation
+inferFixity debug rdrName (ModuleFixityMap m) =
+  if debug
+    then
+      trace
+        (renderFixityJustification opName moduleName m result)
+        result
+    else result
   where
+    result =
+      case Map.lookup opName m of
+        Nothing -> defaultFixityApproximation
+        Just (Given fixityInfo) ->
+          fixityInfoToApproximation fixityInfo
+        Just (FromModuleImports xs) ->
+          let isMatching (provenance, _fixityInfo) =
+                case provenance of
+                  UnqualifiedAndQualified mn ->
+                    maybe True (== mn) moduleName
+                  OnlyQualified mn ->
+                    maybe False (== mn) moduleName
+           in fromMaybe defaultFixityApproximation
+                . foldMap (Just . fixityInfoToApproximation . snd)
+                $ NE.filter isMatching xs
     opName = occOpName (rdrNameOcc rdrName)
     moduleName = case rdrName of
       Qual x _ -> Just (ghcModuleNameToCabal x)
       _ -> Nothing
+
+-- | Render a human-readable account of why a certain 'FixityApproximation'
+-- was chosen for an operator.
+renderFixityJustification ::
+  -- | Operator name
+  OpName ->
+  -- | Qualification of the operator name
+  Maybe ModuleName ->
+  -- | Module fixity map
+  Map OpName FixityProvenance ->
+  -- | The chosen fixity approximation
+  FixityApproximation ->
+  String
+renderFixityJustification opName mqualification m approximation =
+  concat
+    [ "FIXITY analysis of ",
+      show opName,
+      case mqualification of
+        Nothing -> ""
+        Just mn -> " qualified in " ++ show mn,
+      "\n  Provenance: " ++ show (Map.lookup opName m),
+      "\n  Inferred: " ++ show approximation
+    ]
diff --git a/src/Ormolu/Printer.hs b/src/Ormolu/Printer.hs
--- a/src/Ormolu/Printer.hs
+++ b/src/Ormolu/Printer.hs
@@ -19,12 +19,14 @@
 
 -- | Render several source snippets.
 printSnippets ::
+  -- | Whether to print out debug information during printing
+  Bool ->
   -- | Result of parsing
   [SourceSnippet] ->
   PrinterOptsTotal ->
   -- | Resulting rendition
   Text
-printSnippets snippets printerOpts = T.concat . fmap printSnippet $ snippets
+printSnippets debug snippets printerOpts = T.concat . fmap printSnippet $ snippets
   where
     printSnippet = \case
       ParsedSnippet ParseResult {..} ->
@@ -41,4 +43,5 @@
             prSourceType
             prExtensions
             prModuleFixityMap
+            debug
       RawSnippet r -> r
diff --git a/src/Ormolu/Printer/Combinators.hs b/src/Ormolu/Printer/Combinators.hs
--- a/src/Ormolu/Printer/Combinators.hs
+++ b/src/Ormolu/Printer/Combinators.hs
@@ -27,6 +27,7 @@
     inciByFrac,
     askSourceType,
     askModuleFixityMap,
+    askDebug,
     located,
     encloseLocated,
     located',
diff --git a/src/Ormolu/Printer/Internal.hs b/src/Ormolu/Printer/Internal.hs
--- a/src/Ormolu/Printer/Internal.hs
+++ b/src/Ormolu/Printer/Internal.hs
@@ -19,6 +19,7 @@
     declNewline,
     askSourceType,
     askModuleFixityMap,
+    askDebug,
     inci,
     inciBy,
     inciByFrac,
@@ -107,7 +108,9 @@
     -- | Whether the source is a signature or a regular module
     rcSourceType :: SourceType,
     -- | Module fixity map
-    rcModuleFixityMap :: ModuleFixityMap
+    rcModuleFixityMap :: ModuleFixityMap,
+    -- | Whether to print out debug information during printing
+    rcDebug :: !Bool
   }
 
 -- | State context of 'R'.
@@ -179,8 +182,9 @@
   -- | Module fixity map
   ModuleFixityMap ->
   -- | Resulting rendition
+  Bool ->
   Text
-runR (R m) sstream cstream printerOpts sourceType extensions moduleFixityMap =
+runR (R m) sstream cstream printerOpts sourceType extensions moduleFixityMap debug =
   TL.toStrict . toLazyText . scBuilder $ execState (runReaderT m rc) sc
   where
     rc =
@@ -192,7 +196,8 @@
           rcPrinterOpts = printerOpts,
           rcExtensions = extensions,
           rcSourceType = sourceType,
-          rcModuleFixityMap = moduleFixityMap
+          rcModuleFixityMap = moduleFixityMap,
+          rcDebug = debug
         }
     sc =
       SC
@@ -400,6 +405,11 @@
 -- | Retrieve the module fixity map.
 askModuleFixityMap :: R ModuleFixityMap
 askModuleFixityMap = R (asks rcModuleFixityMap)
+
+-- | Retrieve whether we should print out certain debug information while
+-- printing.
+askDebug :: R Bool
+askDebug = R (asks rcDebug)
 
 -- | Like 'inci', but indents by exactly the given number of steps.
 inciBy :: Int -> R () -> R ()
diff --git a/src/Ormolu/Printer/Meat/Declaration/Data.hs b/src/Ormolu/Printer/Meat/Declaration/Data.hs
--- a/src/Ormolu/Printer/Meat/Declaration/Data.hs
+++ b/src/Ormolu/Printer/Meat/Declaration/Data.hs
@@ -52,74 +52,78 @@
   txt $ case style of
     Associated -> mempty
     Free -> " instance"
-  case unLoc <$> dd_cType of
-    Nothing -> pure ()
-    Just (CType prag header (type_, _)) -> do
-      space
-      p_sourceText prag
-      case header of
-        Nothing -> pure ()
-        Just (Header h _) -> space *> p_sourceText h
-      space
-      p_sourceText type_
-      txt " #-}"
   let constructorSpans = getLocA name : fmap getTyVarLoc tyVars
       sigSpans = maybeToList . fmap getLocA $ dd_kindSig
+      contextSpans = maybeToList . fmap getLocA $ dd_ctxt
+      ctypeSpans = maybeToList . fmap getLocA $ dd_cType
       declHeaderSpans =
-        maybeToList (getLocA <$> dd_ctxt) ++ constructorSpans ++ sigSpans
-  switchLayout declHeaderSpans $ do
-    breakpoint
-    inci $ do
-      case dd_ctxt of
-        Nothing -> pure ()
-        Just ctxt -> do
-          located ctxt p_hsContext
-          space
-          txt "=>"
-          breakpoint
-      switchLayout constructorSpans $
-        p_infixDefHelper
-          (isInfix fixity)
-          True
-          (p_rdrName name)
-          (p_tyVar <$> tyVars)
-      forM_ dd_kindSig $ \k -> do
-        space
-        token'dcolon
+        constructorSpans ++ sigSpans ++ contextSpans ++ ctypeSpans
+  switchLayout declHeaderSpans . inci $ do
+    case unLoc <$> dd_cType of
+      Nothing -> pure ()
+      Just (CType prag header (type_, _)) -> do
         breakpoint
-        inci $ located k p_hsType
+        p_sourceText prag
+        case header of
+          Nothing -> pure ()
+          Just (Header h _) -> space *> p_sourceText h
+        space
+        p_sourceText type_
+        txt " #-}"
+    breakpoint
+    forM_ dd_ctxt p_lhsContext
+    switchLayout constructorSpans $
+      p_infixDefHelper
+        (isInfix fixity)
+        True
+        (p_rdrName name)
+        (p_tyVar <$> tyVars)
+    forM_ dd_kindSig $ \k -> do
+      space
+      token'dcolon
+      breakpoint
+      inci $ located k p_hsType
   let dd_cons' = case dd_cons of
         NewTypeCon a -> [a]
         DataTypeCons _ as -> as
       gadt = isJust dd_kindSig || any (isGadt . unLoc) dd_cons'
-  unless (null dd_cons') $
-    if gadt
-      then inci $ do
-        switchLayout declHeaderSpans $ do
+  case dd_cons' of
+    [] -> pure ()
+    first_dd_cons : _ ->
+      if gadt
+        then inci $ do
+          switchLayout declHeaderSpans $ do
+            breakpoint
+            txt "where"
           breakpoint
-          txt "where"
-        breakpoint
-        sepSemi (located' (p_conDecl False)) dd_cons'
-      else switchLayout (getLocA name : (getLocA <$> dd_cons')) . inci $ do
-        let singleConstRec = isSingleConstRec dd_cons'
-        if hasHaddocks dd_cons'
-          then newline
-          else
-            if singleConstRec
-              then space
-              else breakpoint
-        equals
-        space
-        layout <- getLayout
-        let s =
-              if layout == MultiLine || hasHaddocks dd_cons'
-                then newline >> txt "|" >> space
-                else space >> txt "|" >> space
-            sitcc' =
-              if hasHaddocks dd_cons' || not singleConstRec
-                then sitcc
-                else id
-        sep s (sitcc' . located' (p_conDecl singleConstRec)) dd_cons'
+          sepSemi (located' (p_conDecl False)) dd_cons'
+        else switchLayout (getLocA name : (getLocA <$> dd_cons')) . inci $ do
+          let singleConstRec = isSingleConstRec dd_cons'
+              compactLayoutAroundEquals =
+                onTheSameLine
+                  (getLocA name)
+                  (combineSrcSpans' (conDeclConsSpans (unLoc first_dd_cons)))
+              conDeclConsSpans = \case
+                ConDeclGADT {..} -> getLocA <$> con_names
+                ConDeclH98 {..} -> getLocA con_name :| []
+          if hasHaddocks dd_cons'
+            then newline
+            else
+              if singleConstRec && compactLayoutAroundEquals
+                then space
+                else breakpoint
+          equals
+          space
+          layout <- getLayout
+          let s =
+                if layout == MultiLine || hasHaddocks dd_cons'
+                  then newline >> txt "|" >> space
+                  else space >> txt "|" >> space
+              sitcc' =
+                if hasHaddocks dd_cons' || not singleConstRec
+                  then sitcc
+                  else id
+          sep s (sitcc' . located' (p_conDecl singleConstRec)) dd_cons'
   unless (null dd_derivs) breakpoint
   inci $ sep newline (located' p_hsDerivingClause) dd_derivs
 
@@ -168,48 +172,49 @@
         startTypeAnnotationDecl quantifiedTy id p_hsType
   ConDeclH98 {..} -> do
     mapM_ (p_hsDoc Pipe True) con_doc
-    let conDeclWithContextSpn =
+    let conNameSpn = getLocA con_name
+        conNameWithContextSpn =
           [ RealSrcSpan real Strict.Nothing
             | Just (EpaSpan real _) <- matchAddEpAnn AnnForall <$> epAnnAnns con_ext
           ]
             <> fmap getLocA con_ex_tvs
             <> maybeToList (fmap getLocA con_mb_cxt)
-            <> conDeclSpn
-        conDeclSpn = getLocA con_name : conArgsSpans
+            <> [conNameSpn]
+        conDeclSpn = conNameSpn : conArgsSpans
           where
             conArgsSpans = case con_args of
               PrefixCon [] xs -> getLocA . hsScaledThing <$> xs
               PrefixCon (v : _) _ -> absurd v
               RecCon l -> [getLocA l]
               InfixCon x y -> getLocA . hsScaledThing <$> [x, y]
-    switchLayout conDeclWithContextSpn $ do
+    switchLayout conNameWithContextSpn $ do
       when con_forall $ do
         p_forallBndrs ForAllInvis p_hsTyVarBndr con_ex_tvs
         breakpoint
         indent <- getPrinterOpt poIndentation
         vlayout (pure ()) . txt $ Text.replicate (indent - 2) " "
       forM_ con_mb_cxt p_lhsContext
-      switchLayout conDeclSpn $ case con_args of
-        PrefixCon [] xs -> do
-          p_rdrName con_name
-          let args = hsScaledThing <$> xs
-              argsHaveDocs = conArgsHaveHaddocks args
-              delimiter = if argsHaveDocs then newline else breakpoint
-          unless (null xs) delimiter
-          inci . sitcc $
-            sep delimiter (sitcc . located' p_hsType) args
-        PrefixCon (v : _) _ -> absurd v
-        RecCon l -> do
+    switchLayout conDeclSpn $ case con_args of
+      PrefixCon [] xs -> do
+        p_rdrName con_name
+        let args = hsScaledThing <$> xs
+            argsHaveDocs = conArgsHaveHaddocks args
+            delimiter = if argsHaveDocs then newline else breakpoint
+        unless (null xs) delimiter
+        inci . sitcc $
+          sep delimiter (sitcc . located' p_hsType) args
+      PrefixCon (v : _) _ -> absurd v
+      RecCon l -> do
+        p_rdrName con_name
+        breakpoint
+        inciIf (not singleConstRec) (located l p_conDeclFields)
+      InfixCon (HsScaled _ x) (HsScaled _ y) -> do
+        located x p_hsType
+        breakpoint
+        inci $ do
           p_rdrName con_name
-          breakpoint
-          inciIf (not singleConstRec) (located l p_conDeclFields)
-        InfixCon (HsScaled _ x) (HsScaled _ y) -> do
-          located x p_hsType
-          breakpoint
-          inci $ do
-            p_rdrName con_name
-            space
-            located y p_hsType
+          space
+          located y p_hsType
 
 p_lhsContext ::
   LHsContext GhcPs ->
@@ -231,15 +236,23 @@
   HsDerivingClause GhcPs ->
   R ()
 p_hsDerivingClause HsDerivingClause {..} = do
+  singleDerivingParens <- getPrinterOpt poSingleDerivingParens
+
   txt "deriving"
   let derivingWhat = located deriv_clause_tys $ \case
-        DctSingle NoExtField sigTy -> parens N $ located sigTy p_hsSigType
-        DctMulti NoExtField sigTys ->
-          parens N $
-            sep
-              commaDel
-              (sitcc . located' p_hsSigType)
-              sigTys
+        DctSingle NoExtField sigTy
+          | DerivingAlways <- singleDerivingParens -> parens N $ located sigTy p_hsSigType
+          | otherwise -> located sigTy p_hsSigType
+        DctMulti NoExtField sigTys
+          | [sigTy] <- sigTys,
+            DerivingNever <- singleDerivingParens ->
+              located sigTy p_hsSigType
+          | otherwise ->
+              parens N $
+                sep
+                  commaDel
+                  (sitcc . located' p_hsSigType)
+                  sigTys
   space
   case deriv_clause_strategy of
     Nothing -> do
diff --git a/src/Ormolu/Printer/Meat/Declaration/Value.hs b/src/Ormolu/Printer/Meat/Declaration/Value.hs
--- a/src/Ormolu/Printer/Meat/Declaration/Value.hs
+++ b/src/Ormolu/Printer/Meat/Declaration/Value.hs
@@ -353,10 +353,11 @@
       inci (sequence_ (intersperse breakpoint (located' (p_hsCmdTop N) <$> cmds)))
   HsCmdArrForm _ form Infix _ [left, right] -> do
     modFixityMap <- askModuleFixityMap
+    debug <- askDebug
     let opTree = BinaryOpBranches (cmdOpTree left) form (cmdOpTree right)
     p_cmdOpTree
       s
-      (reassociateOpTree (getOpName . unLoc) modFixityMap opTree)
+      (reassociateOpTree debug (getOpName . unLoc) modFixityMap opTree)
   HsCmdArrForm _ _ Infix _ _ -> notImplemented "HsCmdArrForm"
   HsCmdApp _ cmd expr -> do
     located cmd (p_hsCmd' Applicand s)
@@ -368,8 +369,8 @@
     p_case isApp cmdPlacement p_hsCmd e mgroup
   HsCmdLamCase _ variant mgroup ->
     p_lamcase isApp variant cmdPlacement p_hsCmd mgroup
-  HsCmdIf _ _ if' then' else' ->
-    p_if cmdPlacement p_hsCmd if' then' else'
+  HsCmdIf anns _ if' then' else' ->
+    p_if cmdPlacement p_hsCmd anns if' then' else'
   HsCmdLet _ letToken localBinds _ c ->
     p_let (s == S) p_hsCmd letToken localBinds c
   HsCmdDo _ es -> do
@@ -699,10 +700,11 @@
       located (hswc_body a) p_hsType
   OpApp _ x op y -> do
     modFixityMap <- askModuleFixityMap
+    debug <- askDebug
     let opTree = BinaryOpBranches (exprOpTree x) op (exprOpTree y)
     p_exprOpTree
       s
-      (reassociateOpTree (getOpName . unLoc) modFixityMap opTree)
+      (reassociateOpTree debug (getOpName . unLoc) modFixityMap opTree)
   NegApp _ e _ -> do
     negativeLiterals <- isExtensionEnabled NegativeLiterals
     let isLiteral = case unLoc e of
@@ -751,8 +753,8 @@
     p_unboxedSum N tag arity (located e p_hsExpr)
   HsCase _ e mgroup ->
     p_case isApp exprPlacement p_hsExpr e mgroup
-  HsIf _ if' then' else' ->
-    p_if exprPlacement p_hsExpr if' then' else'
+  HsIf anns if' then' else' ->
+    p_if exprPlacement p_hsExpr anns if' then' else'
   HsMultiIf _ guards -> do
     txt "if"
     breakpoint
@@ -988,6 +990,8 @@
   (body -> Placement) ->
   -- | Render
   (body -> R ()) ->
+  -- | Annotations
+  EpAnn AnnsIf ->
   -- | If
   LHsExpr GhcPs ->
   -- | Then
@@ -995,21 +999,47 @@
   -- | Else
   LocatedA body ->
   R ()
-p_if placer render if' then' else' = do
+p_if placer render epAnn if' then' else' = do
   txt "if"
   space
   located if' p_hsExpr
   breakpoint
   inci $ do
-    txt "then"
+    locatedToken thenSpan "then"
     space
-    located then' $ \x ->
-      placeHanging (placer x) (render x)
+    placeHangingLocated thenSpan then'
     breakpoint
-    txt "else"
+    locatedToken elseSpan "else"
     space
-    located else' $ \x ->
-      placeHanging (placer x) (render x)
+    placeHangingLocated elseSpan else'
+  where
+    (thenSpan, elseSpan, commentSpans) =
+      case epAnn of
+        EpAnn {anns = AnnsIf {aiThen, aiElse}, comments} ->
+          ( loc' $ epaLocationRealSrcSpan aiThen,
+            loc' $ epaLocationRealSrcSpan aiElse,
+            map (anchor . getLoc) $
+              case comments of
+                EpaComments cs -> cs
+                EpaCommentsBalanced pre post -> pre <> post
+          )
+        EpAnnNotUsed ->
+          (noSrcSpan, noSrcSpan, [])
+
+    locatedToken tokenSpan token =
+      located (L tokenSpan ()) $ \_ -> txt token
+
+    betweenSpans spanA spanB s = spanA < s && s < spanB
+
+    placeHangingLocated tokenSpan bodyLoc@(L _ body) = do
+      let bodySpan = getLoc' bodyLoc
+          hasComments = fromMaybe False $ do
+            tokenRealSpan <- srcSpanToRealSrcSpan tokenSpan
+            bodyRealSpan <- srcSpanToRealSrcSpan bodySpan
+            pure $ any (betweenSpans tokenRealSpan bodyRealSpan) commentSpans
+          placement = if hasComments then Normal else placer body
+      switchLayout [tokenSpan, bodySpan] $
+        placeHanging placement (located bodyLoc render)
 
 p_let ::
   -- | True if in do-block
diff --git a/src/Ormolu/Printer/Meat/Type.hs b/src/Ormolu/Printer/Meat/Type.hs
--- a/src/Ormolu/Printer/Meat/Type.hs
+++ b/src/Ormolu/Printer/Meat/Type.hs
@@ -121,9 +121,10 @@
       sep (space >> txt "|" >> breakpoint) (sitcc . located' p_hsType) xs
   HsOpTy _ _ x op y -> do
     modFixityMap <- askModuleFixityMap
+    debug <- askDebug
     let opTree = BinaryOpBranches (tyOpTree x) op (tyOpTree y)
     p_tyOpTree
-      (reassociateOpTree (Just . unLoc) modFixityMap opTree)
+      (reassociateOpTree debug (Just . unLoc) modFixityMap opTree)
   HsParTy _ t ->
     parens N $ sitcc $ located t p_hsType
   HsIParamTy _ n t -> sitcc $ do
diff --git a/src/Ormolu/Printer/Operators.hs b/src/Ormolu/Printer/Operators.hs
--- a/src/Ormolu/Printer/Operators.hs
+++ b/src/Ormolu/Printer/Operators.hs
@@ -90,6 +90,8 @@
 -- Users are expected to first construct an initial 'OpTree', then
 -- re-associate it using this function before printing.
 reassociateOpTree ::
+  -- | Whether to print debug info regarding fixity inference
+  Bool ->
   -- | How to get name of an operator
   (op -> Maybe RdrName) ->
   -- | Fixity Map
@@ -98,14 +100,16 @@
   OpTree ty op ->
   -- | Re-associated 'OpTree', with added context and info around operators
   OpTree ty (OpInfo op)
-reassociateOpTree getOpName modFixityMap =
+reassociateOpTree debug getOpName modFixityMap =
   reassociateFlatOpTree
     . makeFlatOpTree
-    . addFixityInfo modFixityMap getOpName
+    . addFixityInfo debug modFixityMap getOpName
 
 -- | Wrap every operator of the tree with 'OpInfo' to carry the information
 -- about its fixity (extracted from the specified fixity map).
 addFixityInfo ::
+  -- | Whether to print debug info regarding fixity inference
+  Bool ->
   -- | Fixity map for operators
   ModuleFixityMap ->
   -- | How to get the name of an operator
@@ -114,10 +118,10 @@
   OpTree ty op ->
   -- | 'OpTree', with fixity info wrapped around each operator
   OpTree ty (OpInfo op)
-addFixityInfo _ _ (OpNode n) = OpNode n
-addFixityInfo modFixityMap getOpName (OpBranches exprs ops) =
+addFixityInfo _ _ _ (OpNode n) = OpNode n
+addFixityInfo debug modFixityMap getOpName (OpBranches exprs ops) =
   OpBranches
-    (addFixityInfo modFixityMap getOpName <$> exprs)
+    (addFixityInfo debug modFixityMap getOpName <$> exprs)
     (toOpInfo <$> ops)
   where
     toOpInfo o = OpInfo o mrdrName fixityApproximation
@@ -125,7 +129,7 @@
         mrdrName = getOpName o
         fixityApproximation = case mrdrName of
           Nothing -> defaultFixityApproximation
-          Just rdrName -> inferFixity rdrName modFixityMap
+          Just rdrName -> inferFixity debug rdrName modFixityMap
 
 -- | Given a 'OpTree' of any shape, produce a flat 'OpTree', where every
 -- node and operator is directly connected to the root.
diff --git a/src/Ormolu/Utils.hs b/src/Ormolu/Utils.hs
--- a/src/Ormolu/Utils.hs
+++ b/src/Ormolu/Utils.hs
@@ -172,6 +172,9 @@
 instance HasSrcSpan SrcSpan where
   loc' = id
 
+instance HasSrcSpan RealSrcSpan where
+  loc' l = RealSrcSpan l Strict.Nothing
+
 instance HasSrcSpan (SrcSpanAnn' ann) where
   loc' = locA
 
diff --git a/tests/Ormolu/Config/PrinterOptsSpec.hs b/tests/Ormolu/Config/PrinterOptsSpec.hs
--- a/tests/Ormolu/Config/PrinterOptsSpec.hs
+++ b/tests/Ormolu/Config/PrinterOptsSpec.hs
@@ -50,7 +50,8 @@
 import Text.PrettyPrint qualified as Doc
 import Text.Printf (printf)
 
-data TestGroup = forall a.
+data TestGroup
+  = forall a.
   TestGroup
   { label :: String,
     -- | When True, takes input from 'input-multi.hs' instead of 'input.hs', where sections
@@ -195,6 +196,15 @@
           isMulti = False,
           testCases = allOptions,
           updateConfig = \parens opts -> opts {poSingleConstraintParens = pure parens},
+          showTestCase = show,
+          testCaseSuffix = suffix1,
+          checkIdempotence = True
+        },
+      TestGroup
+        { label = "single-deriving-parens",
+          isMulti = False,
+          testCases = allOptions,
+          updateConfig = \parens opts -> opts {poSingleDerivingParens = pure parens},
           showTestCase = show,
           testCaseSuffix = suffix1,
           checkIdempotence = True
diff --git a/tests/Ormolu/ConfigSpec.hs b/tests/Ormolu/ConfigSpec.hs
--- a/tests/Ormolu/ConfigSpec.hs
+++ b/tests/Ormolu/ConfigSpec.hs
@@ -7,7 +7,7 @@
 import Data.List.NonEmpty qualified as NonEmpty
 import Data.Map qualified as Map
 import Data.Yaml qualified as Yaml
-import Ormolu.Config (FourmoluConfig (..))
+import Ormolu.Config (FourmoluConfig (..), poIndentation, resolvePrinterOpts)
 import Ormolu.Fixity (ModuleReexports (..))
 import Test.Hspec
 
@@ -26,3 +26,8 @@
               [ ("Foo", NonEmpty.fromList [(Nothing, "Bar2"), (Nothing, "Bar1")])
               ]
       cfgFileReexports config `shouldBe` ModuleReexports expected
+    it "applies configurations in correct order" $ do
+      let opts1 = mempty {poIndentation = Just 2}
+          opts2 = mempty {poIndentation = Just 4}
+          configs = [opts1, opts2]
+      poIndentation (resolvePrinterOpts configs) `shouldBe` 4
diff --git a/tests/Ormolu/FixitySpec.hs b/tests/Ormolu/FixitySpec.hs
--- a/tests/Ormolu/FixitySpec.hs
+++ b/tests/Ormolu/FixitySpec.hs
@@ -261,7 +261,7 @@
   where
     actualResult =
       fmap
-        (\(k, _) -> (k, inferFixity k resultMap))
+        (\(k, _) -> (k, inferFixity False k resultMap))
         expectedResult
     resultMap =
       moduleFixityMap
diff --git a/tests/Ormolu/Integration/FixitySpec.hs b/tests/Ormolu/Integration/FixitySpec.hs
--- a/tests/Ormolu/Integration/FixitySpec.hs
+++ b/tests/Ormolu/Integration/FixitySpec.hs
@@ -61,7 +61,7 @@
         testInputFileName = "test-0-input.hs",
         testArgs = [],
         testUseConfig = False,
-        testExpectedFileName = "test-0-no-extra-info-expected.hs"
+        testExpectedFileName = "test-0-ugly-expected.hs"
       },
     Test
       { testLabel = "File #0 works with manual fixity info",
@@ -76,6 +76,13 @@
         testArgs = ["--package", "base"],
         testUseConfig = True,
         testExpectedFileName = "test-0-with-fixity-info-expected.hs"
+      },
+    Test
+      { testLabel = "File #0 works when CLI overrides .ormolu",
+        testInputFileName = "test-0-input.hs",
+        testArgs = ["--package", "base", "--fixity", "infixr 5 .=", "--no-cabal"],
+        testUseConfig = True,
+        testExpectedFileName = "test-0-ugly-expected.hs"
       },
     Test
       { testLabel = "File #1 works with no extra info",
diff --git a/tests/Ormolu/OpTreeSpec.hs b/tests/Ormolu/OpTreeSpec.hs
--- a/tests/Ormolu/OpTreeSpec.hs
+++ b/tests/Ormolu/OpTreeSpec.hs
@@ -31,7 +31,7 @@
     removeOpInfo (OpNode x) = OpNode x
     removeOpInfo (OpBranches exprs ops) =
       OpBranches (removeOpInfo <$> exprs) (opiOp <$> ops)
-    actualOutputTree = reassociateOpTree convertName modFixityMap inputTree
+    actualOutputTree = reassociateOpTree False convertName modFixityMap inputTree
     modFixityMap = ModuleFixityMap (Map.map Given (Map.fromList fixities))
     convertName = Just . mkRdrUnqual . mkOccName varName . T.unpack . unOpName