Implement -Woperator-whitespace (#18834)

This patch implements two related warnings:

  -Woperator-whitespace-ext-conflict
      warns on uses of infix operators that would be parsed
      differently were a particular GHC extension enabled

  -Woperator-whitespace
      warns on prefix, suffix, and tight infix uses of infix
      operators

Updates submodules: haddock, containers.

5 files changed, 48 insertions, 0 deletions

diff --git a/testsuite/tests/parser/should_compile/T18834a.hs b/testsuite/tests/parser/should_compile/T18834a.hs
new file mode 100644
index 0000000000..7666173d20
--- /dev/null
+++ b/testsuite/tests/parser/should_compile/T18834a.hs
@@ -0,0 +1,8 @@
+module T18834a where
+
+(%) = ($)
+($$) = ($)
+
+x = even $0
+y = even $$0
+z = even %0
diff --git a/testsuite/tests/parser/should_compile/T18834a.stderr b/testsuite/tests/parser/should_compile/T18834a.stderr
new file mode 100644
index 0000000000..2fd8f5903d
--- /dev/null
+++ b/testsuite/tests/parser/should_compile/T18834a.stderr
@@ -0,0 +1,15 @@
+
+T18834a.hs:6:10: warning: [-Woperator-whitespace-ext-conflict (in -Wdefault)]
+    The prefix use of a ‘$’ would denote an untyped splice
+      were the TemplateHaskell extension enabled.
+    Suggested fix: add whitespace after the ‘$’.
+
+T18834a.hs:7:10: warning: [-Woperator-whitespace-ext-conflict (in -Wdefault)]
+    The prefix use of a ‘$$’ would denote a typed splice
+      were the TemplateHaskell extension enabled.
+    Suggested fix: add whitespace after the ‘$$’.
+
+T18834a.hs:8:10: warning: [-Woperator-whitespace-ext-conflict (in -Wdefault)]
+    The prefix use of a ‘%’ would denote a multiplicity annotation
+      were the LinearTypes extension enabled.
+    Suggested fix: add whitespace after the ‘%’.
diff --git a/testsuite/tests/parser/should_compile/T18834b.hs b/testsuite/tests/parser/should_compile/T18834b.hs
new file mode 100644
index 0000000000..8a020b8b5f
--- /dev/null
+++ b/testsuite/tests/parser/should_compile/T18834b.hs
@@ -0,0 +1,8 @@
+{-# OPTIONS -Woperator-whitespace #-}
+
+module T18834b where
+
+f a b = a+ b
+g a b = a +b
+h a b = a+b
+k a b = a + b  -- this one is OK, no warning
diff --git a/testsuite/tests/parser/should_compile/T18834b.stderr b/testsuite/tests/parser/should_compile/T18834b.stderr
new file mode 100644
index 0000000000..9ec4f81bb4
--- /dev/null
+++ b/testsuite/tests/parser/should_compile/T18834b.stderr
@@ -0,0 +1,15 @@
+
+T18834b.hs:5:10: warning: [-Woperator-whitespace]
+    The suffix use of a ‘+’ might be repurposed as special syntax
+      by a future language extension.
+    Suggested fix: add whitespace around it.
+
+T18834b.hs:6:11: warning: [-Woperator-whitespace]
+    The prefix use of a ‘+’ might be repurposed as special syntax
+      by a future language extension.
+    Suggested fix: add whitespace around it.
+
+T18834b.hs:7:10: warning: [-Woperator-whitespace]
+    The tight infix use of a ‘+’ might be repurposed as special syntax
+      by a future language extension.
+    Suggested fix: add whitespace around it.
diff --git a/testsuite/tests/parser/should_compile/all.T b/testsuite/tests/parser/should_compile/all.T
index 48e1136daa..f63a3f95d9 100644
--- a/testsuite/tests/parser/should_compile/all.T
+++ b/testsuite/tests/parser/should_compile/all.T
@@ -170,3 +170,5 @@ test('proposal-229f',
 
 test('T15730a', normal, compile_and_run, [''])
 test('T18130', normal, compile, [''])
+test('T18834a', normal, compile, [''])
+test('T18834b', normal, compile, [''])