Compatibility macro detection for the -Wimplicit-fallthrough diagnostic.

Summary:
When issuing a diagnostic message for the -Wimplicit-fallthrough diagnostics, always try to find the latest macro, defined at the point of fallthrough, which is immediately expanded to "[[clang::fallthrough]]", and use it's name instead of the actual sequence.

Known issues: 
  * uses PP.getSpelling() to compare macro definition with a string (anyone can suggest a convenient way to fill a token array, or maybe lex it in runtime?);
  * this can be generalized and used in other similar cases, any ideas where it should reside then?

Reviewers: doug.gregor, rsmith

Reviewed By: rsmith

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D50

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164858 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 139 insertions, 0 deletions

diff --git a/test/SemaCXX/switch-implicit-fallthrough-macro.cpp b/test/SemaCXX/switch-implicit-fallthrough-macro.cpp
new file mode 100644
index 0000000000..add212fcf5
--- /dev/null
+++ b/test/SemaCXX/switch-implicit-fallthrough-macro.cpp
@@ -0,0 +1,139 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wimplicit-fallthrough -DCOMMAND_LINE_FALLTHROUGH=[[clang::fallthrough]] %s
+
+int fallthrough_compatibility_macro_from_command_line(int n) {
+  switch (n) {
+    case 0:
+      n = n * 10;
+    case 1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert 'COMMAND_LINE_FALLTHROUGH;' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+      ;
+  }
+  return n;
+}
+
+#ifdef __clang__
+#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
+#define COMPATIBILITY_FALLTHROUGH   [ [ /* test */  clang /* test */ \
+    ::  fallthrough  ]  ]    // testing whitespace and comments in macro definition
+#endif
+#endif
+
+#ifndef COMPATIBILITY_FALLTHROUGH
+#define COMPATIBILITY_FALLTHROUGH do { } while (0)
+#endif
+
+int fallthrough_compatibility_macro_from_source(int n) {
+  switch (n) {
+    case 0:
+      n = n * 20;
+    case 1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert 'COMPATIBILITY_FALLTHROUGH;' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+      ;
+  }
+  return n;
+}
+
+// Deeper macro substitution
+#define M1 [[clang::fallthrough]]
+#ifdef __clang__
+#define M2 M1
+#else
+#define M2
+#endif
+
+#define WRONG_MACRO1 clang::fallthrough
+#define WRONG_MACRO2 [[clang::fallthrough]
+#define WRONG_MACRO3 [[clang::fall through]]
+#define WRONG_MACRO4 [[clang::fallthrough]]]
+
+int fallthrough_compatibility_macro_in_macro(int n) {
+  switch (n) {
+    case 0:
+      n = n * 20;
+    case 1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert 'M1;' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+                                                                          // there was an idea that this ^ should be M2
+      ;
+  }
+  return n;
+}
+
+#undef M1
+#undef M2
+#undef COMPATIBILITY_FALLTHROUGH
+#undef COMMAND_LINE_FALLTHROUGH
+
+int fallthrough_compatibility_macro_undefined(int n) {
+  switch (n) {
+    case 0:
+      n = n * 20;
+    case 1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert '[[clang::fallthrough]];' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+      ;
+  }
+#define TOO_LATE [[clang::fallthrough]]
+  return n;
+}
+#undef TOO_LATE
+
+#define MACRO_WITH_HISTORY 11111111
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY [[clang::fallthrough]]
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY 2222222
+
+int fallthrough_compatibility_macro_history(int n) {
+  switch (n) {
+    case 0:
+      n = n * 20;
+#undef MACRO_WITH_HISTORY
+    case 1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert '[[clang::fallthrough]];' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+      ;
+#define MACRO_WITH_HISTORY [[clang::fallthrough]]
+  }
+  return n;
+}
+
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY 11111111
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY [[clang::fallthrough]]
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY 2222222
+#undef MACRO_WITH_HISTORY
+
+int fallthrough_compatibility_macro_history2(int n) {
+  switch (n) {
+    case 0:
+      n = n * 20;
+#define MACRO_WITH_HISTORY [[clang::fallthrough]]
+    case 1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert 'MACRO_WITH_HISTORY;' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+      ;
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY 3333333
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY 4444444
+#undef MACRO_WITH_HISTORY
+#define MACRO_WITH_HISTORY 5555555
+  }
+  return n;
+}
+
+template<const int N>
+int fallthrough_compatibility_macro_history_template(int n) {
+  switch (N * n) {
+    case 0:
+      n = n * 20;
+#define MACRO_WITH_HISTORY2 [[clang::fallthrough]]
+    case 1: // expected-warning{{unannotated fall-through between switch labels}} expected-note{{insert 'MACRO_WITH_HISTORY2;' to silence this warning}} expected-note{{insert 'break;' to avoid fall-through}}
+      ;
+#undef MACRO_WITH_HISTORY2
+#define MACRO_WITH_HISTORY2 3333333
+  }
+  return n;
+}
+
+#undef MACRO_WITH_HISTORY2
+#define MACRO_WITH_HISTORY2 4444444
+#undef MACRO_WITH_HISTORY2
+#define MACRO_WITH_HISTORY2 5555555
+
+void f() {
+  fallthrough_compatibility_macro_history_template<1>(0); // expected-note{{in instantiation of function template specialization 'fallthrough_compatibility_macro_history_template<1>' requested here}}
+}