Only use locally bound variables in pattern synonym declarations

Summary:
We were using the unconstrainted `lookupOccRn` function which looked up
any variable in scope. Instead we only want to consider variables brought into
scope by renaming the pattern on the RHS.

A few more changes to make reporting of unbound names suggest the correct
things.

Fixes #13470

Reviewers: simonpj, austin, bgamari

Reviewed By: simonpj

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3377

3 files changed, 29 insertions, 0 deletions

diff --git a/testsuite/tests/patsyn/should_fail/T13470.hs b/testsuite/tests/patsyn/should_fail/T13470.hs
new file mode 100644
index 0000000000..ec263b9f0a
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T13470.hs
@@ -0,0 +1,20 @@
+{-# Language PatternSynonyms #-}
+module T13470 where
+
+
+-- Used to suggest importing not
+pattern XInstrProxy :: (Bool -> Bool) -> a
+pattern XInstrProxy not <- _
+
+
+-- Used to suggest 'tan' from another module
+pattern P nan <- _
+
+
+
+-- Should suggest the inscope similar variable
+pattern P1 x12345 <- Just x123456
+
+
+-- But not this one
+x1234567 = True
diff --git a/testsuite/tests/patsyn/should_fail/T13470.stderr b/testsuite/tests/patsyn/should_fail/T13470.stderr
new file mode 100644
index 0000000000..748b5d1da2
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T13470.stderr
@@ -0,0 +1,8 @@
+
+T13470.hs:7:21: error: Not in scope: ‘not’
+
+T13470.hs:11:11: error: Not in scope: ‘nan’
+
+T13470.hs:16:12: error:
+    Not in scope: ‘x12345’
+    Perhaps you meant ‘x123456’ (line 16)
diff --git a/testsuite/tests/patsyn/should_fail/all.T b/testsuite/tests/patsyn/should_fail/all.T
index f674a8b258..86ec79a50c 100644
--- a/testsuite/tests/patsyn/should_fail/all.T
+++ b/testsuite/tests/patsyn/should_fail/all.T
@@ -35,3 +35,4 @@ test('T12165', normal, compile_fail, [''])
 test('T12819', normal, compile_fail, [''])
 test('UnliftedPSBind', normal, compile_fail, [''])
 test('T13349', normal, compile_fail, [''])
+test('T13470', normal, compile_fail, [''])