Default to -fno-show-warning-groups (re #10752)

As `-fno-show-warning-groups` shows associated warning groups regardless
of whether the respective warning group flag as been passed on the CLI,
the warning-group information may be confusing to users.

At this point, `-fshow-warning-groups` is useful mostly to GHC
developers and possibly GHC users who want to see which warning groups
an emitted warning is part of. (Btw, this is particularly interesting in
combination with `-Weverything` which enables *every* warning flag known
to GHC.)

Consequently, starting with this commit, one has to opt-in via
`-fshow-warning-groups` for GHC to show warning groups.

In order to reduce the testsuite delta in this commit, the
`-fshow-warning-groups` flag has been added to TEST_HC_OPTS.

7 files changed, 21 insertions, 12 deletions

diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs
index ebfd861237..8f9fbbb567 100644
--- a/compiler/main/DynFlags.hs
+++ b/compiler/main/DynFlags.hs
@@ -3617,8 +3617,7 @@ defaultFlags settings
       Opt_ProfCountEntries,
       Opt_RPath,
       Opt_SharedImplib,
-      Opt_SimplPreInlining,
-      Opt_ShowWarnGroups
+      Opt_SimplPreInlining
     ]
 
     ++ [f | (ns,f) <- optLevelFlags, 0 `elem` ns]
diff --git a/docs/users_guide/using-warnings.rst b/docs/users_guide/using-warnings.rst
index 3f24f6a6dc..ffe5a41fb0 100644
--- a/docs/users_guide/using-warnings.rst
+++ b/docs/users_guide/using-warnings.rst
@@ -103,13 +103,14 @@ The following flags are simple ways to select standard "packages" of warnings:
     default, but can be useful to negate a :ghc-flag:`-Werror` flag.
 
 When a warning is emitted, the specific warning flag which controls
-it, as well as the group it belongs to, are shown.
+it is shown.
 
 .. ghc-flag:: -fshow-warning-groups
 
-    Name the group a warning flag belongs to.
+    When showing which flag controls a warning, also show the
+    respective warning group flag(s) that warning is contained in.
 
-    This is enabled by default. Disable with ``-fno-show-warning-groups``.
+    This option is off by default.
 
 The full set of warning options is described below. To turn off any
 warning, simply give the corresponding ``-Wno-...`` option on the
diff --git a/testsuite/mk/test.mk b/testsuite/mk/test.mk
index aa20a42a65..97ceb39cb9 100644
--- a/testsuite/mk/test.mk
+++ b/testsuite/mk/test.mk
@@ -34,7 +34,7 @@ endif
 
 # TEST_HC_OPTS is passed to every invocation of TEST_HC 
 # in nested Makefiles
-TEST_HC_OPTS = -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -no-user-$(GhcPackageDbFlag) -rtsopts $(EXTRA_HC_OPTS)
+TEST_HC_OPTS = -fforce-recomp -dcore-lint -dcmm-lint -dno-debug-output -fshow-warning-groups -no-user-$(GhcPackageDbFlag) -rtsopts $(EXTRA_HC_OPTS)
 
 # The warning suppression flag below is a temporary kludge. While working with
 # tests that contain tabs, please de-tab them so this flag can be eventually
diff --git a/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr b/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr
index a943e48a3b..80b94dca4b 100644
--- a/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr
+++ b/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr
@@ -1,9 +1,9 @@
 
-B.hs:4:1: warning: [-Wmissing-signatures (in -Wall)]
+B.hs:4:1: warning: [-Wmissing-signatures]
     Top-level binding with no type signature:
       answer_to_live_the_universe_and_everything :: Int
 
-B.hs:5:12: warning: [-Wtype-defaults (in -Wall)]
+B.hs:5:12: warning: [-Wtype-defaults]
     • Defaulting the following constraints to type ‘Integer’
         (Enum a0)
           arising from the arithmetic sequence ‘1 .. 23 * 2’ at B.hs:5:12-20
@@ -12,14 +12,14 @@ B.hs:5:12: warning: [-Wtype-defaults (in -Wall)]
       In the first argument of ‘(-)’, namely ‘length [1 .. 23 * 2]’
       In the expression: length [1 .. 23 * 2] - 4
 
-A.hs:7:1: warning: [-Wmissing-signatures (in -Wall)]
+A.hs:7:1: warning: [-Wmissing-signatures]
     Top-level binding with no type signature: main :: IO ()
 
-B.hs:4:1: warning: [-Wmissing-signatures (in -Wall)]
+B.hs:4:1: warning: [-Wmissing-signatures]
     Top-level binding with no type signature:
       answer_to_live_the_universe_and_everything :: Int
 
-B.hs:5:12: warning: [-Wtype-defaults (in -Wall)]
+B.hs:5:12: warning: [-Wtype-defaults]
     • Defaulting the following constraints to type ‘Integer’
         (Enum a0)
           arising from the arithmetic sequence ‘1 .. 23 * 2’ at B.hs:5:12-20
@@ -28,5 +28,5 @@ B.hs:5:12: warning: [-Wtype-defaults (in -Wall)]
       In the first argument of ‘(-)’, namely ‘length [1 .. 23 * 2]’
       In the expression: length [1 .. 23 * 2] - 4
 
-A.hs:7:1: warning: [-Wmissing-signatures (in -Wall)]
+A.hs:7:1: warning: [-Wmissing-signatures]
     Top-level binding with no type signature: main :: IO ()
diff --git a/testsuite/tests/ghci/scripts/T9293.stdout b/testsuite/tests/ghci/scripts/T9293.stdout
index 67fc63058e..02ee22c7e8 100644
--- a/testsuite/tests/ghci/scripts/T9293.stdout
+++ b/testsuite/tests/ghci/scripts/T9293.stdout
@@ -7,6 +7,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should fail, GADTs is not enabled
 options currently set: none.
@@ -21,6 +22,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should work, GADTs is in force from :set
 options currently set: none.
@@ -34,6 +36,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should fail, GADTs is now disabled
 base language is: Haskell2010
@@ -49,6 +52,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should fail, GADTs is only enabled at the prompt
 C :: T Int
diff --git a/testsuite/tests/ghci/scripts/ghci024.stdout b/testsuite/tests/ghci/scripts/ghci024.stdout
index 9fea9464b0..b92adad855 100644
--- a/testsuite/tests/ghci/scripts/ghci024.stdout
+++ b/testsuite/tests/ghci/scripts/ghci024.stdout
@@ -8,6 +8,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fforce-recomp
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
   -Wno-tabs
 ~~~~~~~~~~ Testing :set -a
diff --git a/testsuite/tests/ghci/scripts/ghci057.stdout b/testsuite/tests/ghci/scripts/ghci057.stdout
index 67fc63058e..02ee22c7e8 100644
--- a/testsuite/tests/ghci/scripts/ghci057.stdout
+++ b/testsuite/tests/ghci/scripts/ghci057.stdout
@@ -7,6 +7,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should fail, GADTs is not enabled
 options currently set: none.
@@ -21,6 +22,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should work, GADTs is in force from :set
 options currently set: none.
@@ -34,6 +36,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should fail, GADTs is now disabled
 base language is: Haskell2010
@@ -49,6 +52,7 @@ GHCi-specific dynamic flag settings:
 other dynamic, non-language, flag settings:
   -fno-ghci-history
   -fimplicit-import-qualified
+  -fshow-warning-groups
 warning settings:
 Should fail, GADTs is only enabled at the prompt
 C :: T Int