Fix backticks and parens in multiline function declarations

Function id obtained through pattern matching on ‘FunBind’ should not be
used to print the actual equations because the different ‘RdrNames’ used in
the equations may have different “decorations” (such as backticks and
paretheses) associated with them. It is necessary to use per-equation names
obtained from ‘m_ctxt’ of ‘Match’.

data/examples/declaration/value/function/backticks-lhs-out.hs

@@ -0,0 +1,7 @@
+x `op1` (Just 0) = True
+op1 x (Just _) = False
+op1 x Nothing = undefined
+
+op2 1 y = False
+x `op2` y =
+  True

data/examples/declaration/value/function/backticks-lhs.hs

@@ -0,0 +1,7 @@
+x `op1`            (Just 0) = True
+op1 x (Just _)    =      False
+op1 x       Nothing = undefined
+
+op2 1 y =   False
+x `op2` y =
+        True

data/examples/declaration/value/function/parenthesis-lhs-out.hs

@@ -0,0 +1,9 @@
+(!=!) 2 y = 1
+x !=! y = 2
+
+x ?=? [] = 123
+(?=?) x (_ : []) = 456
+x ?=? _ = f x x
+  where
+    f x 7 = 789
+    x `f` _ = 101

data/examples/declaration/value/function/parenthesis-lhs.hs

@@ -0,0 +1,9 @@
+(!=!) 2 y = 1
+x  !=! y = 2
+
+x ?=? [] = 123
+(?=?)   x   (_:[]) = 456
+x ?=? _ = f x x
+  where
+      f x 7 = 789
+      x `f`  _ = 101

data/examples/declaration/value/pattern-synonyms/explicitely-bidirectional-out.hs

@@ -13,5 +13,4 @@ pattern HeadC' x <-
 pattern Simple <-
   "Simple"
   where
-    Simple =
-      "Complicated"
+    Simple = "Complicated"

src/Ormolu/Printer/Meat/Declaration/Value.hs

@@ -69,8 +69,7 @@ p_funBind
   :: Located RdrName
   -> MatchGroup GhcPs (LHsExpr GhcPs)
   -> R ()
-p_funBind name mgroup =
-  p_matchGroup (Function name) mgroup
+p_funBind name = p_matchGroup (Function name)
 
 p_matchGroup
   :: MatchGroupStyle
@@ -86,11 +85,35 @@ p_matchGroup'
   -> MatchGroup GhcPs (Located body)
   -> R ()
 p_matchGroup' placer pretty style MG {..} =
-  sep newline (located' (\m@Match {..} ->
-    p_match' placer pretty style (isInfixMatch m) (matchStrictness m) m_pats m_grhss))
-    (unLoc mg_alts)
+  sep newline (located' p_Match) (unLoc mg_alts)
+  where
+    p_Match m@Match {..} =
+      p_match'
+        placer
+        pretty
+        (adjustMatchGroupStyle m style)
+        (isInfixMatch m)
+        (matchStrictness m)
+        m_pats
+        m_grhss
+    p_Match _ = notImplemented "XMatch"
 p_matchGroup' _ _ _ (XMatchGroup NoExt) = notImplemented "XMatchGroup"
 
+-- | Function id obtained through pattern matching on 'FunBind' should not
+-- be used to print the actual equations because the different ‘RdrNames’
+-- used in the equations may have different “decorations” (such as backticks
+-- and paretheses) associated with them. It is necessary to use per-equation
+-- names obtained from 'm_ctxt' of 'Match'. This function replaces function
+-- name inside of 'Function' accordingly.
+
+adjustMatchGroupStyle
+  :: Match GhcPs body
+  -> MatchGroupStyle
+  -> MatchGroupStyle
+adjustMatchGroupStyle m = \case
+  Function _ -> (Function . mc_fun . m_ctxt) m
+  style -> style
+
 matchStrictness :: Match id body -> SrcStrictness
 matchStrictness match =
   case m_ctxt match of