From: Aaron Ballman <aaron@aaronballman.com>
Date: Wed, 18 Oct 2017 14:33:27 +0000 (+0000)
Subject: Enable support for the [[fallthrough]] attribute from WG14 N2052 when enabling double... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=644b1eb1f21899b4fd64824391fa597f0ca9dff0;p=clang

Enable support for the [[fallthrough]] attribute from WG14 N2052 when enabling double square bracket attributes in C code.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@316083 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/Basic/Attr.td b/include/clang/Basic/Attr.td
index 5ff08dd700..fd8372bab5 100644
--- a/include/clang/Basic/Attr.td
+++ b/include/clang/Basic/Attr.td
@@ -1009,7 +1009,7 @@ def ExtVectorType : Attr {
 }
 
 def FallThrough : StmtAttr {
-  let Spellings = [CXX11<"", "fallthrough", 201603>,
+  let Spellings = [CXX11<"", "fallthrough", 201603>, C2x<"", "fallthrough">,
                    CXX11<"clang", "fallthrough">];
 //  let Subjects = [NullStmt];
   let Documentation = [FallthroughDocs];
diff --git a/lib/Sema/AnalysisBasedWarnings.cpp b/lib/Sema/AnalysisBasedWarnings.cpp
index 7a31711e72..f004a990a4 100644
--- a/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/lib/Sema/AnalysisBasedWarnings.cpp
@@ -1291,16 +1291,15 @@ static StringRef getFallthroughAttrSpelling(Preprocessor &PP,
 
 static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
                                             bool PerFunction) {
-  // Only perform this analysis when using C++11.  There is no good workflow
-  // for this warning when not using C++11.  There is no good way to silence
-  // the warning (no attribute is available) unless we are using C++11's support
-  // for generalized attributes.  Once could use pragmas to silence the warning,
-  // but as a general solution that is gross and not in the spirit of this
-  // warning.
+  // Only perform this analysis when using [[]] attributes. There is no good
+  // workflow for this warning when not using C++11. There is no good way to
+  // silence the warning (no attribute is available) unless we are using 
+  // [[]] attributes. One could use pragmas to silence the warning, but as a
+  // general solution that is gross and not in the spirit of this warning.
   //
-  // NOTE: This an intermediate solution.  There are on-going discussions on
+  // NOTE: This an intermediate solution. There are on-going discussions on
   // how to properly support this warning outside of C++11 with an annotation.
-  if (!AC.getASTContext().getLangOpts().CPlusPlus11)
+  if (!AC.getASTContext().getLangOpts().DoubleSquareBracketAttributes)
     return;
 
   FallthroughMapper FM(S);
diff --git a/test/Sema/c2x-fallthrough.c b/test/Sema/c2x-fallthrough.c
new file mode 100644
index 0000000000..4a0b22edbf
--- /dev/null
+++ b/test/Sema/c2x-fallthrough.c
@@ -0,0 +1,75 @@
+// RUN: %clang_cc1 -fsyntax-only -fdouble-square-bracket-attributes -verify %s
+
+void f(int n) {
+  switch (n) {
+  case 0:
+    n += 1;
+    [[fallthrough]]; // ok
+  case 1:
+    if (n) {
+      [[fallthrough]]; // ok
+    } else {
+      return;
+    }
+  case 2:
+    for (int n = 0; n != 10; ++n)
+      [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+  case 3:
+    while (1)
+      [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+  case 4:
+    while (0)
+      [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+  case 5:
+    do [[fallthrough]]; while (1); // expected-error {{does not directly precede switch label}}
+  case 6:
+    do [[fallthrough]]; while (0); // expected-error {{does not directly precede switch label}}
+  case 7:
+    switch (n) {
+    case 0:
+      // FIXME: This should be an error, even though the next thing we do is to
+      // fall through in an outer switch statement.
+      [[fallthrough]];
+    }
+  case 8:
+    [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+    goto label;
+  label:
+  case 9:
+    n += 1;
+  case 10: // no warning, -Wimplicit-fallthrough is not enabled in this test, and does not need to
+           // be enabled for these diagnostics to be produced.
+    break;
+  }
+}
+
+[[fallthrough]] typedef int n; // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+typedef int [[fallthrough]] n; // expected-error {{'fallthrough' attribute cannot be applied to types}}
+typedef int n [[fallthrough]]; // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+
+enum [[fallthrough]] E { // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+  One
+};
+struct [[fallthrough]] S { // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+  int i;
+};
+
+[[fallthrough]] // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+void g(void) {
+  [[fallthrough]] int n; // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+  [[fallthrough]] ++n; // expected-error-re {{{{^}}fallthrough attribute is only allowed on empty statements}}
+
+  switch (n) {
+    // FIXME: This should be an error.
+    [[fallthrough]];
+    return;
+
+  case 0:
+    [[fallthrough, fallthrough]]; // expected-error {{multiple times}}
+  case 1:
+    [[fallthrough(0)]]; // expected-error {{argument list}}
+  case 2:
+    break;
+  }
+}
+