Add -fdefer-typed-holes flag which defers hole errors to runtime.

Summary:
As proposed by Richard on Trac. This patch adds a new flag -fdefer-typed-holes
and changes the semantics of the -fno-warn-typed-holes flag.

To summarise, by default GHC has typed holes enabled and produces a compile
error when it encounters a typed hole.

When -fdefer-type-errors OR -fdefer-typed-holes is enabled, hole errors are
converted to warnings and result in runtime errors when evaluated.

The warning flag -fwarn-typed-holes is on by default. Without -fdefer-type-errors
or -fdefer-typed-holes this flag is a no-op, since typed holes are an error
under these conditions. If either of the defer flags are enabled (converting
typed hole errors into warnings) the -fno-warn-typed-holes flag disables the
warnings. This means compilation silently succeeds and evaluating a hole will
produce a runtime error.

The rationale behind allowing typed holes warnings to be silenced is that tools
like Syntastic for vim highlight warnings and hole warnings may be undesirable.

Signed-off-by: Merijn Verstraaten <merijn@inconsistent.nl>

Test Plan: validate

Reviewers: austin, simonpj, thomie

Reviewed By: simonpj, thomie

Subscribers: Fuuzetsu, thomie, carter

Differential Revision: https://phabricator.haskell.org/D442

GHC Trac Issues: #9497

Conflicts:
	compiler/main/DynFlags.hs

17 files changed, 54 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_compile/T9497a.hs b/testsuite/tests/typecheck/should_compile/T9497a.hs
new file mode 100644
index 0000000000..fa30912352
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T9497a.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = _main
diff --git a/testsuite/tests/typecheck/should_compile/T9497a.stderr b/testsuite/tests/typecheck/should_compile/T9497a.stderr
new file mode 100644
index 0000000000..763fbaea33
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T9497a.stderr
@@ -0,0 +1,6 @@
+
+T9497a.hs:2:8: Warning:
+    Found hole ‘_main’ with type: IO ()
+    Relevant bindings include main :: IO () (bound at T9497a.hs:2:1)
+    In the expression: _main
+    In an equation for ‘main’: main = _main
diff --git a/testsuite/tests/typecheck/should_compile/T9497b.hs b/testsuite/tests/typecheck/should_compile/T9497b.hs
new file mode 100644
index 0000000000..fa30912352
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T9497b.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = _main
diff --git a/testsuite/tests/typecheck/should_compile/T9497b.stderr b/testsuite/tests/typecheck/should_compile/T9497b.stderr
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T9497b.stderr
diff --git a/testsuite/tests/typecheck/should_compile/T9497c.hs b/testsuite/tests/typecheck/should_compile/T9497c.hs
new file mode 100644
index 0000000000..fa30912352
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T9497c.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = _main
diff --git a/testsuite/tests/typecheck/should_compile/T9497c.stderr b/testsuite/tests/typecheck/should_compile/T9497c.stderr
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T9497c.stderr
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index 8acfa4aa53..b16ff4309d 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -428,3 +428,6 @@ test('T9404b', normal, compile, [''])
 test('T7220', normal, compile, [''])
 test('T7220a', normal, compile_fail, [''])
 test('T9151', normal, compile, [''])
+test('T9497a', normal, compile, ['-fdefer-typed-holes'])
+test('T9497b', normal, compile, ['-fdefer-typed-holes -fno-warn-typed-holes'])
+test('T9497c', normal, compile, ['-fdefer-type-errors -fno-warn-typed-holes'])
diff --git a/testsuite/tests/typecheck/should_fail/T9497d.hs b/testsuite/tests/typecheck/should_fail/T9497d.hs
new file mode 100644
index 0000000000..fa30912352
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T9497d.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = _main
diff --git a/testsuite/tests/typecheck/should_fail/T9497d.stderr b/testsuite/tests/typecheck/should_fail/T9497d.stderr
new file mode 100644
index 0000000000..4f18ce9497
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T9497d.stderr
@@ -0,0 +1,6 @@
+
+T9497d.hs:2:8:
+    Found hole ‘_main’ with type: IO ()
+    Relevant bindings include main :: IO () (bound at T9497d.hs:2:1)
+    In the expression: _main
+    In an equation for ‘main’: main = _main
diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index 96396d27c4..81ea3d25b9 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -343,3 +343,4 @@ test('T9774', normal, compile_fail, [''])
 test('T9318', normal, compile_fail, [''])
 test('T9201', normal, compile_fail, [''])
 test('T9109', normal, compile_fail, [''])
+test('T9497d', normal, compile_fail, ['-fdefer-type-errors -fno-defer-typed-holes'])
diff --git a/testsuite/tests/typecheck/should_run/T9497a-run.hs b/testsuite/tests/typecheck/should_run/T9497a-run.hs
new file mode 100644
index 0000000000..fa30912352
--- /dev/null
+++ b/testsuite/tests/typecheck/should_run/T9497a-run.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = _main
diff --git a/testsuite/tests/typecheck/should_run/T9497a-run.stderr b/testsuite/tests/typecheck/should_run/T9497a-run.stderr
new file mode 100644
index 0000000000..aae24cf396
--- /dev/null
+++ b/testsuite/tests/typecheck/should_run/T9497a-run.stderr
@@ -0,0 +1,7 @@
+T9497a-run: T9497a-run.hs:2:8:
+    Found hole ‘_main’ with type: IO ()
+    Relevant bindings include
+      main :: IO () (bound at T9497a-run.hs:2:1)
+    In the expression: _main
+    In an equation for ‘main’: main = _main
+(deferred type error)
diff --git a/testsuite/tests/typecheck/should_run/T9497b-run.hs b/testsuite/tests/typecheck/should_run/T9497b-run.hs
new file mode 100644
index 0000000000..fa30912352
--- /dev/null
+++ b/testsuite/tests/typecheck/should_run/T9497b-run.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = _main
diff --git a/testsuite/tests/typecheck/should_run/T9497b-run.stderr b/testsuite/tests/typecheck/should_run/T9497b-run.stderr
new file mode 100644
index 0000000000..62d858f879
--- /dev/null
+++ b/testsuite/tests/typecheck/should_run/T9497b-run.stderr
@@ -0,0 +1,7 @@
+T9497b-run: T9497b-run.hs:2:8:
+    Found hole ‘_main’ with type: IO ()
+    Relevant bindings include
+      main :: IO () (bound at T9497b-run.hs:2:1)
+    In the expression: _main
+    In an equation for ‘main’: main = _main
+(deferred type error)
diff --git a/testsuite/tests/typecheck/should_run/T9497c-run.hs b/testsuite/tests/typecheck/should_run/T9497c-run.hs
new file mode 100644
index 0000000000..fa30912352
--- /dev/null
+++ b/testsuite/tests/typecheck/should_run/T9497c-run.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = _main
diff --git a/testsuite/tests/typecheck/should_run/T9497c-run.stderr b/testsuite/tests/typecheck/should_run/T9497c-run.stderr
new file mode 100644
index 0000000000..be5d9472f7
--- /dev/null
+++ b/testsuite/tests/typecheck/should_run/T9497c-run.stderr
@@ -0,0 +1,7 @@
+T9497c-run: T9497c-run.hs:2:8:
+    Found hole ‘_main’ with type: IO ()
+    Relevant bindings include
+      main :: IO () (bound at T9497c-run.hs:2:1)
+    In the expression: _main
+    In an equation for ‘main’: main = _main
+(deferred type error)
diff --git a/testsuite/tests/typecheck/should_run/all.T b/testsuite/tests/typecheck/should_run/all.T
index 5da7c8b169..53c97ea1a8 100755
--- a/testsuite/tests/typecheck/should_run/all.T
+++ b/testsuite/tests/typecheck/should_run/all.T
@@ -112,3 +112,6 @@ test('TcTypeNatSimpleRun', normal, compile_and_run, [''])
 test('T8119', normal, ghci_script, ['T8119.script'])
 test('T8492', normal, compile_and_run, [''])
 test('T8739', normal, compile_and_run, [''])
+test('T9497a-run', [exit_code(1)], compile_and_run, ['-fdefer-typed-holes'])
+test('T9497b-run', [exit_code(1)], compile_and_run, ['-fdefer-typed-holes -fno-warn-typed-holes'])
+test('T9497c-run', [exit_code(1)], compile_and_run, ['-fdefer-type-errors -fno-warn-typed-holes'])