Conditionally show plural "s" in warnings

Redundant constraints and defaulting warnings had "constraint(s)" in
their messages; the "s" is now conditional based on the number of things
warned about.

Reviewers: hvr, austin, bgamari

Reviewed By: bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1647

7 files changed, 120 insertions, 66 deletions

diff --git a/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr b/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr
index 69b9996223..d778df2783 100644
--- a/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr
+++ b/testsuite/tests/ghc-api/apirecomp001/apirecomp001.stderr
@@ -1,32 +1,32 @@
 
-B.hs:4:1: Warning:
+B.hs:4:1: warning:
     Top-level binding with no type signature:
       answer_to_live_the_universe_and_everything :: Int
 
-B.hs:5:12: Warning:
-    Defaulting the following constraint(s) to type ‘Integer’
-      (Enum a0)
-        arising from the arithmetic sequence ‘1 .. 23 * 2’ at B.hs:5:12-20
-      (Num a0) arising from the literal ‘1’ at B.hs:5:13
-    In the first argument of ‘length’, namely ‘[1 .. 23 * 2]’
-    In the first argument of ‘(-)’, namely ‘length [1 .. 23 * 2]’
-    In the expression: length [1 .. 23 * 2] - 4
+B.hs:5:12: warning:
+    • Defaulting the following constraints to type ‘Integer’
+        (Enum a0)
+          arising from the arithmetic sequence ‘1 .. 23 * 2’ at B.hs:5:12-20
+        (Num a0) arising from the literal ‘1’ at B.hs:5:13
+    • In the first argument of ‘length’, namely ‘[1 .. 23 * 2]’
+      In the first argument of ‘(-)’, namely ‘length [1 .. 23 * 2]’
+      In the expression: length [1 .. 23 * 2] - 4
 
-A.hs:7:1: Warning:
+A.hs:7:1: warning:
     Top-level binding with no type signature: main :: IO ()
 
-B.hs:4:1: Warning:
+B.hs:4:1: warning:
     Top-level binding with no type signature:
       answer_to_live_the_universe_and_everything :: Int
 
-B.hs:5:12: Warning:
-    Defaulting the following constraint(s) to type ‘Integer’
-      (Enum a0)
-        arising from the arithmetic sequence ‘1 .. 23 * 2’ at B.hs:5:12-20
-      (Num a0) arising from the literal ‘1’ at B.hs:5:13
-    In the first argument of ‘length’, namely ‘[1 .. 23 * 2]’
-    In the first argument of ‘(-)’, namely ‘length [1 .. 23 * 2]’
-    In the expression: length [1 .. 23 * 2] - 4
+B.hs:5:12: warning:
+    • Defaulting the following constraints to type ‘Integer’
+        (Enum a0)
+          arising from the arithmetic sequence ‘1 .. 23 * 2’ at B.hs:5:12-20
+        (Num a0) arising from the literal ‘1’ at B.hs:5:13
+    • In the first argument of ‘length’, namely ‘[1 .. 23 * 2]’
+      In the first argument of ‘(-)’, namely ‘length [1 .. 23 * 2]’
+      In the expression: length [1 .. 23 * 2] - 4
 
-A.hs:7:1: Warning:
+A.hs:7:1: warning:
     Top-level binding with no type signature: main :: IO ()
diff --git a/testsuite/tests/parser/should_compile/T2245.stderr b/testsuite/tests/parser/should_compile/T2245.stderr
index 53b738832f..1f5f87f7c7 100644
--- a/testsuite/tests/parser/should_compile/T2245.stderr
+++ b/testsuite/tests/parser/should_compile/T2245.stderr
@@ -1,22 +1,22 @@
 
-T2245.hs:4:10: Warning:
-    No explicit implementation for
-      ‘+’, ‘*’, ‘abs’, ‘signum’, ‘fromInteger’, and (either ‘negate’
-                                                            or
-                                                            ‘-’)
-    In the instance declaration for ‘Num T’
+T2245.hs:4:10: warning:
+    • No explicit implementation for
+        ‘+’, ‘*’, ‘abs’, ‘signum’, ‘fromInteger’, and (either ‘negate’
+                                                              or
+                                                              ‘-’)
+    • In the instance declaration for ‘Num T’
 
-T2245.hs:5:10: Warning:
-    No explicit implementation for
-      ‘fromRational’ and (either ‘recip’ or ‘/’)
-    In the instance declaration for ‘Fractional T’
+T2245.hs:5:10: warning:
+    • No explicit implementation for
+        ‘fromRational’ and (either ‘recip’ or ‘/’)
+    • In the instance declaration for ‘Fractional T’
 
-T2245.hs:7:29: Warning:
-    Defaulting the following constraint(s) to type ‘T’
-      (Fractional b0)
-        arising from the literal ‘1e400’ at T2245.hs:7:29-33
-      (Ord b0) arising from a use of ‘<’ at T2245.hs:7:27
-      (Read b0) arising from a use of ‘read’ at T2245.hs:7:38-41
-    In the second argument of ‘(<)’, namely ‘1e400’
-    In the first argument of ‘(.)’, namely ‘(< 1e400)’
-    In the second argument of ‘(.)’, namely ‘(< 1e400) . read’
+T2245.hs:7:29: warning:
+    • Defaulting the following constraints to type ‘T’
+        (Fractional b0)
+          arising from the literal ‘1e400’ at T2245.hs:7:29-33
+        (Ord b0) arising from a use of ‘<’ at T2245.hs:7:27
+        (Read b0) arising from a use of ‘read’ at T2245.hs:7:38-41
+    • In the second argument of ‘(<)’, namely ‘1e400’
+      In the first argument of ‘(.)’, namely ‘(< 1e400)’
+      In the second argument of ‘(.)’, namely ‘(< 1e400) . read’
diff --git a/testsuite/tests/typecheck/should_compile/T10971a.stderr b/testsuite/tests/typecheck/should_compile/T10971a.stderr
index 4cb2b72a40..7ca7680c52 100644
--- a/testsuite/tests/typecheck/should_compile/T10971a.stderr
+++ b/testsuite/tests/typecheck/should_compile/T10971a.stderr
@@ -3,11 +3,11 @@ T10971a.hs:7:1: warning:
     Top-level binding with no type signature: f :: forall a. [a] -> Int
 
 T10971a.hs:7:11: warning:
-    Defaulting the following constraint(s) to type ‘[]’
-      Foldable t0 arising from a use of ‘length’
-    In the expression: length x
-    In the expression: \ x -> length x
-    In an equation for ‘f’: f = \ x -> length x
+    • Defaulting the following constraint to type ‘[]’
+        Foldable t0 arising from a use of ‘length’
+    • In the expression: length x
+      In the expression: \ x -> length x
+      In an equation for ‘f’: f = \ x -> length x
 
 T10971a.hs:8:1: warning:
     Top-level binding with no type signature:
@@ -18,11 +18,11 @@ T10971a.hs:8:6: warning:
       defined at T10971a.hs:7:1
 
 T10971a.hs:8:13: warning:
-    Defaulting the following constraint(s) to type ‘[]’
-      Traversable t0 arising from a use of ‘fmapDefault’
-    In the expression: fmapDefault f x
-    In the expression: \ f x -> fmapDefault f x
-    In an equation for ‘g’: g = \ f x -> fmapDefault f x
+    • Defaulting the following constraint to type ‘[]’
+        Traversable t0 arising from a use of ‘fmapDefault’
+    • In the expression: fmapDefault f x
+      In the expression: \ f x -> fmapDefault f x
+      In an equation for ‘g’: g = \ f x -> fmapDefault f x
 
 T10971a.hs:9:1: warning:
     Top-level binding with no type signature:
@@ -33,10 +33,10 @@ T10971a.hs:9:6: warning:
       defined at T10971a.hs:7:1
 
 T10971a.hs:9:31: warning:
-    Defaulting the following constraint(s) to type ‘[]’
-      (Foldable t0) arising from a use of ‘length’ at T10971a.hs:9:31-36
-      (Traversable t0)
-        arising from a use of ‘fmapDefault’ at T10971a.hs:9:14-24
-    In the expression: length x
-    In the expression: (fmapDefault f x, length x)
-    In the expression: \ f x -> (fmapDefault f x, length x)
+    • Defaulting the following constraints to type ‘[]’
+        (Foldable t0) arising from a use of ‘length’ at T10971a.hs:9:31-36
+        (Traversable t0)
+          arising from a use of ‘fmapDefault’ at T10971a.hs:9:14-24
+    • In the expression: length x
+      In the expression: (fmapDefault f x, length x)
+      In the expression: \ f x -> (fmapDefault f x, length x)
diff --git a/testsuite/tests/typecheck/should_fail/tcfail204.stderr b/testsuite/tests/typecheck/should_fail/tcfail204.stderr
index e8ecfc0024..b6ef584387 100644
--- a/testsuite/tests/typecheck/should_fail/tcfail204.stderr
+++ b/testsuite/tests/typecheck/should_fail/tcfail204.stderr
@@ -1,13 +1,13 @@
 
-tcfail204.hs:10:15: Warning:
-    Defaulting the following constraint(s) to type ‘Double’
-      (Fractional a0)
-        arising from the literal ‘6.3’ at tcfail204.hs:10:15-17
-      (RealFrac a0)
-        arising from a use of ‘ceiling’ at tcfail204.hs:10:7-13
-    In the first argument of ‘ceiling’, namely ‘6.3’
-    In the expression: ceiling 6.3
-    In an equation for ‘foo’: foo = ceiling 6.3
+tcfail204.hs:10:15: warning:
+    • Defaulting the following constraints to type ‘Double’
+        (Fractional a0)
+          arising from the literal ‘6.3’ at tcfail204.hs:10:15-17
+        (RealFrac a0)
+          arising from a use of ‘ceiling’ at tcfail204.hs:10:7-13
+    • In the first argument of ‘ceiling’, namely ‘6.3’
+      In the expression: ceiling 6.3
+      In an equation for ‘foo’: foo = ceiling 6.3
 
-<no location info>: 
+<no location info>: error: 
 Failing due to -Werror.
diff --git a/testsuite/tests/warnings/should_compile/PluralS.hs b/testsuite/tests/warnings/should_compile/PluralS.hs
new file mode 100644
index 0000000000..89b5dbffcd
--- /dev/null
+++ b/testsuite/tests/warnings/should_compile/PluralS.hs
@@ -0,0 +1,27 @@
+-- Test purpose:
+--
+-- Ensure the plural "s" in warnings is only shown if there are more than
+-- one entries
+
+{-# OPTIONS_GHC -Wredundant-constraints #-}
+{-# OPTIONS_GHC -Wtype-defaults #-}
+
+module PluralS () where
+
+
+
+-- Defaulting type classes
+
+defaultingNum = 123 `seq` ()
+
+defaultingNumAndShow = show 123
+
+
+
+-- Redundant constraints
+
+redundantNum :: (Num a, Num a) => a
+redundantNum = 123
+
+redundantMultiple :: (Num a, Show a, Num a, Eq a, Eq a) => a
+redundantMultiple = 123
diff --git a/testsuite/tests/warnings/should_compile/PluralS.stderr b/testsuite/tests/warnings/should_compile/PluralS.stderr
new file mode 100644
index 0000000000..c013e7b73d
--- /dev/null
+++ b/testsuite/tests/warnings/should_compile/PluralS.stderr
@@ -0,0 +1,26 @@
+
+PluralS.hs:15:17: warning:
+    • Defaulting the following constraint to type ‘Integer’
+        Num t0 arising from the literal ‘123’
+    • In the first argument of ‘seq’, namely ‘123’
+      In the expression: 123 `seq` ()
+      In an equation for ‘defaultingNum’: defaultingNum = 123 `seq` ()
+
+PluralS.hs:17:29: warning:
+    • Defaulting the following constraints to type ‘Integer’
+        (Num a0) arising from the literal ‘123’ at PluralS.hs:17:29-31
+        (Show a0) arising from a use of ‘show’ at PluralS.hs:17:24-27
+    • In the first argument of ‘show’, namely ‘123’
+      In the expression: show 123
+      In an equation for ‘defaultingNumAndShow’:
+          defaultingNumAndShow = show 123
+
+PluralS.hs:23:1: warning:
+    • Redundant constraint: Num a
+    • In the type signature for:
+           redundantNum :: (Num a, Num a) => a
+
+PluralS.hs:26:1: warning:
+    • Redundant constraints: (Show a, Num a, Eq a, Eq a)
+    • In the type signature for:
+           redundantMultiple :: (Num a, Show a, Num a, Eq a, Eq a) => a
diff --git a/testsuite/tests/warnings/should_compile/all.T b/testsuite/tests/warnings/should_compile/all.T
index f60468e6ca..a2b1860ba4 100644
--- a/testsuite/tests/warnings/should_compile/all.T
+++ b/testsuite/tests/warnings/should_compile/all.T
@@ -7,6 +7,7 @@ test('T9230', normal, compile_without_flag('-fno-warn-tabs'), [''])
 test('T10908', normal, compile, [''])
 test('T11077', normal, compile, ['-fwarn-missing-exported-sigs'])
 test('T11128', normal, compile, [''])
+test('PluralS', normal, compile, [''])
 
 test('DeprU',
 	extra_clean([