ghc generates more user-friendly error messages

Test Plan: Compiled ghc fine.  Opened ghci and fed it invalid code.  It gave the improved error messages in response.

Reviewers: austin

Subscribers: thomie, simonpj, spacekitteh, rwbarton, simonmar, carter

Differential Revision: https://phabricator.haskell.org/D201

10 files changed, 29 insertions, 9 deletions

diff --git a/testsuite/tests/annotations/should_fail/annfail08.stderr b/testsuite/tests/annotations/should_fail/annfail08.stderr
index b2d119de68..0449033685 100644
--- a/testsuite/tests/annotations/should_fail/annfail08.stderr
+++ b/testsuite/tests/annotations/should_fail/annfail08.stderr
@@ -1,9 +1,12 @@
 
 annfail08.hs:9:1:
     No instance for (Data.Data.Data (a0 -> a0))
+      (maybe you haven't applied enough arguments to a function?)
       arising from an annotation
     In the annotation: {-# ANN f (id + 1) #-}
 
 annfail08.hs:9:15:
-    No instance for (Num (a0 -> a0)) arising from a use of ‘+’
+    No instance for (Num (a0 -> a0))
+      (maybe you haven't applied enough arguments to a function?)
+      arising from a use of ‘+’
     In the annotation: {-# ANN f (id + 1) #-}
diff --git a/testsuite/tests/deriving/should_fail/drvfail007.stderr b/testsuite/tests/deriving/should_fail/drvfail007.stderr
index 183a5ff8d5..91cf8bfa38 100644
--- a/testsuite/tests/deriving/should_fail/drvfail007.stderr
+++ b/testsuite/tests/deriving/should_fail/drvfail007.stderr
@@ -1,6 +1,7 @@
 
 drvfail007.hs:4:38:
     No instance for (Eq (Int -> Int))
+      (maybe you haven't applied enough arguments to a function?)
       arising from the first field of ‘Foo’ (type ‘Int -> Int’)
     Possible fix:
       use a standalone 'deriving instance' declaration,
diff --git a/testsuite/tests/ghci.debugger/scripts/break003.stderr b/testsuite/tests/ghci.debugger/scripts/break003.stderr
index 5baf41bcdf..7a9c08ec2f 100644
--- a/testsuite/tests/ghci.debugger/scripts/break003.stderr
+++ b/testsuite/tests/ghci.debugger/scripts/break003.stderr
@@ -1,4 +1,6 @@
 
 <interactive>:5:1:
-    No instance for (Show (t -> t1)) arising from a use of ‘print’
+    No instance for (Show (t -> t1))
+      (maybe you haven't applied enough arguments to a function?)
+      arising from a use of ‘print’
     In a stmt of an interactive GHCi command: print it
diff --git a/testsuite/tests/ghci/scripts/Defer02.stderr b/testsuite/tests/ghci/scripts/Defer02.stderr
index cbd2f3b64d..4f58b02695 100644
--- a/testsuite/tests/ghci/scripts/Defer02.stderr
+++ b/testsuite/tests/ghci/scripts/Defer02.stderr
@@ -27,7 +27,9 @@
     In an equation for ‘c’: c (C2 x) = True
 
 ../../typecheck/should_run/Defer01.hs:28:5: Warning:
-    No instance for (Num (a -> a)) arising from the literal ‘1’
+    No instance for (Num (a -> a))
+      (maybe you haven't applied enough arguments to a function?)
+      arising from the literal ‘1’
     In the expression: 1
     In an equation for ‘d’: d = 1
 
@@ -133,7 +135,9 @@
     In the first argument of ‘c’, namely ‘(C2 True)’
     In the first argument of ‘print’, namely ‘(c (C2 True))’
 *** Exception: ../../typecheck/should_run/Defer01.hs:28:5:
-    No instance for (Num (a -> a)) arising from the literal ‘1’
+    No instance for (Num (a -> a))
+      (maybe you haven't applied enough arguments to a function?)
+      arising from the literal ‘1’
     In the expression: 1
     In an equation for ‘d’: d = 1
 (deferred type error)
diff --git a/testsuite/tests/mdo/should_fail/mdofail005.stderr b/testsuite/tests/mdo/should_fail/mdofail005.stderr
index 548129117a..594fea2a19 100644
--- a/testsuite/tests/mdo/should_fail/mdofail005.stderr
+++ b/testsuite/tests/mdo/should_fail/mdofail005.stderr
@@ -1,2 +1,4 @@
 
-mdofail005.hs:11:14: parse error on input ‘<-’
+mdofail005.hs:11:14:
+    parse error on input ‘<-’
+    Perhaps this statement should be within a 'do' block?
diff --git a/testsuite/tests/parser/should_fail/ParserNoLambdaCase.stderr b/testsuite/tests/parser/should_fail/ParserNoLambdaCase.stderr
index 147c8fef9c..5a3f1cc080 100644
--- a/testsuite/tests/parser/should_fail/ParserNoLambdaCase.stderr
+++ b/testsuite/tests/parser/should_fail/ParserNoLambdaCase.stderr
@@ -1,2 +1,2 @@
 
-ParserNoLambdaCase.hs:3:6: parse error on input ‘case’
+ParserNoLambdaCase.hs:3:5: parse error: naked lambda expression ''
diff --git a/testsuite/tests/parser/should_fail/readFail020.stderr b/testsuite/tests/parser/should_fail/readFail020.stderr
index 0e3bde41da..0c00cdc79b 100644
--- a/testsuite/tests/parser/should_fail/readFail020.stderr
+++ b/testsuite/tests/parser/should_fail/readFail020.stderr
@@ -1,2 +1,3 @@
 
-readFail020.hs:3:16: parse error on input ‘}’
+readFail020.hs:3:5:
+    parse error in let binding: missing required 'in'
diff --git a/testsuite/tests/parser/should_fail/readFail040.stderr b/testsuite/tests/parser/should_fail/readFail040.stderr
index 6cbb3ce525..728090b9ec 100644
--- a/testsuite/tests/parser/should_fail/readFail040.stderr
+++ b/testsuite/tests/parser/should_fail/readFail040.stderr
@@ -1,2 +1,4 @@
 
-readFail040.hs:7:11: parse error on input ‘<-’
+readFail040.hs:7:11:
+    parse error on input ‘<-’
+    Perhaps this statement should be within a 'do' block?
diff --git a/testsuite/tests/rebindable/rebindable6.stderr b/testsuite/tests/rebindable/rebindable6.stderr
index a02563f3ca..b9ae82096b 100644
--- a/testsuite/tests/rebindable/rebindable6.stderr
+++ b/testsuite/tests/rebindable/rebindable6.stderr
@@ -1,6 +1,7 @@
 
 rebindable6.hs:106:17:
     No instance for (HasSeq (IO a -> t0 -> IO b))
+      (maybe you haven't applied enough arguments to a function?)
       arising from a do statement
     The type variable ‘t0’ is ambiguous
     Relevant bindings include
@@ -24,6 +25,7 @@ rebindable6.hs:106:17:
 
 rebindable6.hs:107:17:
     No instance for (HasFail ([Prelude.Char] -> t1))
+      (maybe you haven't applied enough arguments to a function?)
       arising from a do statement
     The type variable ‘t1’ is ambiguous
     Note: there is a potential instance available:
@@ -42,6 +44,7 @@ rebindable6.hs:107:17:
 
 rebindable6.hs:108:17:
     No instance for (HasReturn (b -> t1))
+      (maybe you haven't applied enough arguments to a function?)
       arising from a use of ‘return’
     The type variable ‘t1’ is ambiguous
     Relevant bindings include
diff --git a/testsuite/tests/typecheck/should_fail/T2846b.stderr b/testsuite/tests/typecheck/should_fail/T2846b.stderr
index 34d24ae8f6..ccf4f149ee 100644
--- a/testsuite/tests/typecheck/should_fail/T2846b.stderr
+++ b/testsuite/tests/typecheck/should_fail/T2846b.stderr
@@ -1,5 +1,7 @@
 
 T2846b.hs:5:5:
-    No instance for (Show (Num a0 => a0)) arising from a use of ‘show’
+    No instance for (Show (Num a0 => a0))
+      (maybe you haven't applied enough arguments to a function?)
+      arising from a use of ‘show’
     In the expression: show ([1, 2, 3] :: [Num a => a])
     In an equation for ‘f’: f = show ([1, 2, 3] :: [Num a => a])