New handling of overlapping inst in Safe Haskell

We do much better now due to the newish per-instance flags. Rather than
mark any module that uses `-XOverlappingInstances`,
`-XIncoherentInstances` or the new `OVERLAP*` pragmas as unsafe, we
regard them all as safe and defer the check until an overlap occurs.

An type-class method call that involves overlapping instances is
considered _unsafe_ when:

1) The most specific instance, Ix, is from a module marked `-XSafe`
2) Ix is an orphan instance or a MPTC
3) At least one instance that Ix overlaps, Iy, is:
   a) from a different module than Ix
   AND
   b) Iy is not marked `OVERLAPPABLE`

This check is only enforced in modules compiled with `-XSafe` or
`-XTrustworthy`.

This fixes Safe Haskell to work with the latest overlapping instance
pragmas, and also brings consistent behavior. Previously, Safe Inferred
modules behaved differently than `-XSafe` modules.

1 files changed, 62 insertions, 0 deletions

diff --git a/testsuite/tests/safeHaskell/overlapping/all.T b/testsuite/tests/safeHaskell/overlapping/all.T
new file mode 100644
index 0000000000..c253850ac1
--- /dev/null
+++ b/testsuite/tests/safeHaskell/overlapping/all.T
@@ -0,0 +1,62 @@
+# overlapping tests Safe Haskell's handling of overlapping instances.
+
+# Just do the normal way, SafeHaskell is all in the frontend
+def f( name, opts ):
+  opts.only_ways = ['normal']
+
+setTestOpts(f)
+
+test('SH_Overlap1',
+    [ extra_clean(['SH_Overlap1_A.hi', 'SH_Overlap1_A.o',
+                   'SH_Overlap1_B.hi', 'SH_Overlap1_B.o']) ],
+    multimod_compile_fail, ['SH_Overlap1', ''])
+
+test('SH_Overlap2',
+    [ extra_clean(['SH_Overlap2_A.hi', 'SH_Overlap2_A.o',
+                   'SH_Overlap2_B.hi', 'SH_Overlap2_B.o']) ],
+    multimod_compile_fail, ['SH_Overlap2', ''])
+
+test('SH_Overlap3',
+    [ extra_clean(['SH_Overlap3_A.hi', 'SH_Overlap3_A.o',
+                   'SH_Overlap3_B.hi', 'SH_Overlap3_B.o']) ],
+    multimod_compile, ['SH_Overlap3', ''])
+
+test('SH_Overlap4',
+    [ extra_clean(['SH_Overlap4_A.hi', 'SH_Overlap4_A.o',
+                   'SH_Overlap4_B.hi', 'SH_Overlap4_B.o']) ],
+    multimod_compile, ['SH_Overlap4', ''])
+
+test('SH_Overlap5',
+    [ extra_clean(['SH_Overlap5_A.hi', 'SH_Overlap5_A.o',
+                   'SH_Overlap5_B.hi', 'SH_Overlap5_B.o']) ],
+    multimod_compile_fail, ['SH_Overlap5', ''])
+
+test('SH_Overlap6',
+    [ extra_clean(['SH_Overlap6_A.hi', 'SH_Overlap6_A.o',
+                   'SH_Overlap6_B.hi', 'SH_Overlap6_B.o']) ],
+    multimod_compile_fail, ['SH_Overlap6', ''])
+
+test('SH_Overlap7',
+    [ extra_clean(['SH_Overlap7_A.hi', 'SH_Overlap7_A.o',
+                   'SH_Overlap7_B.hi', 'SH_Overlap7_B.o']) ],
+    multimod_compile_fail, ['SH_Overlap7', '-Werror'])
+
+test('SH_Overlap8',
+    [ extra_clean(['SH_Overlap8_A.hi', 'SH_Overlap8_A.o']) ],
+    multimod_compile, ['SH_Overlap8', ''])
+
+test('SH_Overlap9',
+    [ extra_clean(['SH_Overlap9_A.hi', 'SH_Overlap9_A.o',
+                   'SH_Overlap9_B.hi', 'SH_Overlap9_B.o']) ],
+    multimod_compile, ['SH_Overlap9', '-Werror'])
+
+test('SH_Overlap10',
+    [ extra_clean(['SH_Overlap10_A.hi', 'SH_Overlap10_A.o',
+                   'SH_Overlap10_B.hi', 'SH_Overlap10_B.o']) ],
+    multimod_compile, ['SH_Overlap10', '-Werror'])
+
+test('SH_Overlap11',
+    [ extra_clean(['SH_Overlap11_A.hi', 'SH_Overlap11_A.o',
+                   'SH_Overlap11_B.hi', 'SH_Overlap11_B.o']) ],
+    multimod_compile, ['SH_Overlap11', ''])
+