Print which warning-flag controls an emitted warning.wip/D1934

Summary:
Both gcc and clang tell which warning flag a reported warning can be
controlled with, this patch makes ghc do the same. More generally, this
allows for annotated compiler output, where an optional annotation is
displayed in brackets after the severity.

Fixes T10752.

Reviewers: austin, hvr, goldfire, bgamari

Subscribers: goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D1934

1 files changed, 27 insertions, 15 deletions

diff --git a/compiler/rename/RnSource.hs b/compiler/rename/RnSource.hs
index 4f655090c6..5c5e1b1d3e 100644
--- a/compiler/rename/RnSource.hs
+++ b/compiler/rename/RnSource.hs
@@ -500,10 +500,12 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == pureAName, isAliasMG mg == Just returnMName
-                      -> addWarnNonCanonicalMethod1 "pure" "return"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonadInstances "pure" "return"
 
                       | name == thenAName, isAliasMG mg == Just thenMName
-                      -> addWarnNonCanonicalMethod1 "(*>)" "(>>)"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonadInstances "(*>)" "(>>)"
 
                   _ -> return ()
 
@@ -512,10 +514,12 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == returnMName, isAliasMG mg /= Just pureAName
-                      -> addWarnNonCanonicalMethod2 "return" "pure"
+                      -> addWarnNonCanonicalMethod2
+                            Opt_WarnNonCanonicalMonadInstances "return" "pure"
 
                       | name == thenMName, isAliasMG mg /= Just thenAName
-                      -> addWarnNonCanonicalMethod2 "(>>)" "(*>)"
+                      -> addWarnNonCanonicalMethod2
+                            Opt_WarnNonCanonicalMonadInstances "(>>)" "(*>)"
 
                   _ -> return ()
 
@@ -540,7 +544,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == failMName, isAliasMG mg == Just failMName_preMFP
-                      -> addWarnNonCanonicalMethod1 "fail" "Control.Monad.fail"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonadFailInstances "fail"
+                            "Control.Monad.fail"
 
                   _ -> return ()
 
@@ -549,8 +555,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == failMName_preMFP, isAliasMG mg /= Just failMName
-                      -> addWarnNonCanonicalMethod2 "fail"
-                                                    "Control.Monad.Fail.fail"
+                      -> addWarnNonCanonicalMethod2
+                            Opt_WarnNonCanonicalMonadFailInstances "fail"
+                            "Control.Monad.Fail.fail"
                   _ -> return ()
 
       | otherwise = return ()
@@ -574,7 +581,8 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == sappendName, isAliasMG mg == Just mappendName
-                      -> addWarnNonCanonicalMethod1 "(<>)" "mappend"
+                      -> addWarnNonCanonicalMethod1
+                            Opt_WarnNonCanonicalMonoidInstances "(<>)" "mappend"
 
                   _ -> return ()
 
@@ -583,7 +591,8 @@ checkCanonicalInstances cls poly_ty mbinds = do
               case mbind of
                   FunBind { fun_id = L _ name, fun_matches = mg }
                       | name == mappendName, isAliasMG mg /= Just sappendName
-                      -> addWarnNonCanonicalMethod2NoDefault "mappend" "(<>)"
+                      -> addWarnNonCanonicalMethod2NoDefault
+                            Opt_WarnNonCanonicalMonoidInstances "mappend" "(<>)"
 
                   _ -> return ()
 
@@ -599,8 +608,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
     isAliasMG _ = Nothing
 
     -- got "lhs = rhs" but expected something different
-    addWarnNonCanonicalMethod1 lhs rhs = do
-        addWarn $ vcat [ text "Noncanonical" <+>
+    addWarnNonCanonicalMethod1 flag lhs rhs = do
+        addWarn flag $ vcat
+                       [ text "Noncanonical" <+>
                          quotes (text (lhs ++ " = " ++ rhs)) <+>
                          text "definition detected"
                        , instDeclCtxt1 poly_ty
@@ -610,8 +620,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
                        ]
 
     -- expected "lhs = rhs" but got something else
-    addWarnNonCanonicalMethod2 lhs rhs = do
-        addWarn $ vcat [ text "Noncanonical" <+>
+    addWarnNonCanonicalMethod2 flag lhs rhs = do
+        addWarn flag $ vcat
+                       [ text "Noncanonical" <+>
                          quotes (text lhs) <+>
                          text "definition detected"
                        , instDeclCtxt1 poly_ty
@@ -621,8 +632,9 @@ checkCanonicalInstances cls poly_ty mbinds = do
                        ]
 
     -- like above, but method has no default impl
-    addWarnNonCanonicalMethod2NoDefault lhs rhs = do
-        addWarn $ vcat [ text "Noncanonical" <+>
+    addWarnNonCanonicalMethod2NoDefault flag lhs rhs = do
+        addWarn flag $ vcat
+                       [ text "Noncanonical" <+>
                          quotes (text lhs) <+>
                          text "definition detected"
                        , instDeclCtxt1 poly_ty