[commit: ghc] master: Add suggestion for PatternSynonyms parse error (fixes #12429) (4b1f072)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/4b1f0721ce164d079848d1f8890630dbbf4cbf7a/ghc

>---------------------------------------------------------------

commit 4b1f0721ce164d079848d1f8890630dbbf4cbf7a
Author: Rupert Horlick <ruperthorlick at gmail.com>
Date:   Thu Mar 2 16:35:31 2017 -0500

    Add suggestion for PatternSynonyms parse error (fixes #12429)
    
    Reviewers: austin, bgamari
    
    Reviewed By: bgamari
    
    Subscribers: thomie
    
    Differential Revision: https://phabricator.haskell.org/D3261


>---------------------------------------------------------------

4b1f0721ce164d079848d1f8890630dbbf4cbf7a
 compiler/parser/Lexer.x                          | 4 ++++
 testsuite/tests/parser/should_fail/T12429.hs     | 3 +++
 testsuite/tests/parser/should_fail/T12429.stderr | 7 +++++++
 testsuite/tests/parser/should_fail/all.T         | 1 +
 4 files changed, 15 insertions(+)

diff --git a/compiler/parser/Lexer.x b/compiler/parser/Lexer.x
index 3c5d98d..6f91f44 100644
--- a/compiler/parser/Lexer.x
+++ b/compiler/parser/Lexer.x
@@ -2394,8 +2394,12 @@ srcParseErr options buf len
               $$ ppWhen (token == "=")
                         (text "Perhaps you need a 'let' in a 'do' block?"
                          $$ text "e.g. 'let x = 5' instead of 'x = 5'")
+              $$ ppWhen (not ps_enabled && pattern == "pattern") -- #12429
+                        (text "Perhaps you intended to use PatternSynonyms")
   where token = lexemeToString (offsetBytes (-len) buf) len
+        pattern = lexemeToString (offsetBytes (-len - 8) buf) 7
         th_enabled = extopt LangExt.TemplateHaskell options
+        ps_enabled = extopt LangExt.PatternSynonyms options
 
 -- Report a parse failure, giving the span of the previous token as
 -- the location of the error.  This is the entry point for errors
diff --git a/testsuite/tests/parser/should_fail/T12429.hs b/testsuite/tests/parser/should_fail/T12429.hs
new file mode 100644
index 0000000..3e0496b
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/T12429.hs
@@ -0,0 +1,3 @@
+module X where
+  import Data.Text (pattern Y)
+  x = 3
diff --git a/testsuite/tests/parser/should_fail/T12429.stderr b/testsuite/tests/parser/should_fail/T12429.stderr
new file mode 100644
index 0000000..fde11ec
--- /dev/null
+++ b/testsuite/tests/parser/should_fail/T12429.stderr
@@ -0,0 +1,7 @@
+
+testsuite/tests/parser/should_fail/T12429.hs:2:29: error:
+    parse error on input ‘Y’
+    Perhaps you intended to use PatternSynonyms
+  |
+2 |   import Data.Text (pattern Y)
+  |                             ^
diff --git a/testsuite/tests/parser/should_fail/all.T b/testsuite/tests/parser/should_fail/all.T
index ca23d3b..e515e2f 100644
--- a/testsuite/tests/parser/should_fail/all.T
+++ b/testsuite/tests/parser/should_fail/all.T
@@ -94,3 +94,4 @@ test('T10196Fail2', normal, compile_fail, [''])
 test('T10498a', normal, compile_fail, [''])
 test('T10498b', normal, compile_fail, [''])
 test('T12051', normal, compile_fail, [''])
+test('T12429', normal, compile_fail, [''])