P0188R1: add support for standard [[fallthrough]] attribute. This is almost

exactly the same as clang's existing [[clang::fallthrough]] attribute, which
has been updated to have the same semantics. The one significant difference
is that [[fallthrough]] is ill-formed if it's not used immediately before a
switch label (even when -Wimplicit-fallthrough is disabled). To support that,
we now build a CFG of any function that uses a '[[fallthrough]];' statement
to check.

In passing, fix some bugs with our support for statement attributes -- in
particular, diagnose their use on declarations, rather than asserting.

llvm-svn: 262881

4 files changed, 61 insertions, 20 deletions

diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 5f74343fbd9..fcb12f6cebf 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -1071,6 +1071,34 @@ namespace {
   };
 } // anonymous namespace
 
+static StringRef getFallthroughAttrSpelling(Preprocessor &PP,
+                                            SourceLocation Loc) {
+  TokenValue FallthroughTokens[] = {
+    tok::l_square, tok::l_square,
+    PP.getIdentifierInfo("fallthrough"),
+    tok::r_square, tok::r_square
+  };
+
+  TokenValue ClangFallthroughTokens[] = {
+    tok::l_square, tok::l_square, PP.getIdentifierInfo("clang"),
+    tok::coloncolon, PP.getIdentifierInfo("fallthrough"),
+    tok::r_square, tok::r_square
+  };
+
+  bool PreferClangAttr = !PP.getLangOpts().CPlusPlus1z;
+
+  StringRef MacroName;
+  if (PreferClangAttr)
+    MacroName = PP.getLastMacroWithSpelling(Loc, ClangFallthroughTokens);
+  if (MacroName.empty())
+    MacroName = PP.getLastMacroWithSpelling(Loc, FallthroughTokens);
+  if (MacroName.empty() && !PreferClangAttr)
+    MacroName = PP.getLastMacroWithSpelling(Loc, ClangFallthroughTokens);
+  if (MacroName.empty())
+    MacroName = PreferClangAttr ? "[[clang::fallthrough]]" : "[[fallthrough]]";
+  return MacroName;
+}
+
 static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
                                             bool PerFunction) {
   // Only perform this analysis when using C++11.  There is no good workflow
@@ -1129,15 +1157,7 @@ static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
         }
         if (!(B->empty() && Term && isa<BreakStmt>(Term))) {
           Preprocessor &PP = S.getPreprocessor();
-          TokenValue Tokens[] = {
-            tok::l_square, tok::l_square, PP.getIdentifierInfo("clang"),
-            tok::coloncolon, PP.getIdentifierInfo("fallthrough"),
-            tok::r_square, tok::r_square
-          };
-          StringRef AnnotationSpelling = "[[clang::fallthrough]]";
-          StringRef MacroName = PP.getLastMacroWithSpelling(L, Tokens);
-          if (!MacroName.empty())
-            AnnotationSpelling = MacroName;
+          StringRef AnnotationSpelling = getFallthroughAttrSpelling(PP, L);
           SmallString<64> TextToInsert(AnnotationSpelling);
           TextToInsert += "; ";
           S.Diag(L, diag::note_insert_fallthrough_fixit) <<
@@ -1151,7 +1171,7 @@ static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
   }
 
   for (const auto *F : FM.getFallthroughStmts())
-    S.Diag(F->getLocStart(), diag::warn_fallthrough_attr_invalid_placement);
+    S.Diag(F->getLocStart(), diag::err_fallthrough_attr_invalid_placement);
 }
 
 static bool isInLoop(const ASTContext &Ctx, const ParentMap &PM,
@@ -2038,7 +2058,8 @@ AnalysisBasedWarnings::IssueWarnings(sema::AnalysisBasedWarnings::Policy P,
       !Diags.isIgnored(diag::warn_unannotated_fallthrough, D->getLocStart());
   bool FallThroughDiagPerFunction = !Diags.isIgnored(
       diag::warn_unannotated_fallthrough_per_function, D->getLocStart());
-  if (FallThroughDiagFull || FallThroughDiagPerFunction) {
+  if (FallThroughDiagFull || FallThroughDiagPerFunction ||
+      fscope->HasFallthroughStmt) {
     DiagnoseSwitchLabelsFallthrough(S, AC, !FallThroughDiagFull);
   }
 
diff --git a/clang/lib/Sema/AttributeList.cpp b/clang/lib/Sema/AttributeList.cpp
index 3c61c95ad8e..cae9393f9f3 100644
--- a/clang/lib/Sema/AttributeList.cpp
+++ b/clang/lib/Sema/AttributeList.cpp
@@ -159,6 +159,7 @@ struct ParsedAttrInfo {
   unsigned HasCustomParsing : 1;
   unsigned IsTargetSpecific : 1;
   unsigned IsType : 1;
+  unsigned IsStmt : 1;
   unsigned IsKnownToGCC : 1;
 
   bool (*DiagAppertainsToDecl)(Sema &S, const AttributeList &Attr,
@@ -204,6 +205,10 @@ bool AttributeList::isTypeAttr() const {
   return getInfo(*this).IsType;
 }
 
+bool AttributeList::isStmtAttr() const {
+  return getInfo(*this).IsStmt;
+}
+
 bool AttributeList::existsInTarget(const TargetInfo &Target) const {
   return getInfo(*this).ExistsInTarget(Target);
 }
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index ce78ab00926..1fca27f8b95 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -2467,7 +2467,7 @@ static void handleWarnUnusedResult(Sema &S, Decl *D, const AttributeList &Attr)
   // about using it as an extension.
   if (!S.getLangOpts().CPlusPlus1z && Attr.isCXX11Attribute() &&
       !Attr.getScopeName())
-    S.Diag(Attr.getLoc(), diag::ext_nodiscard_attr_is_a_cxx1z_extension);
+    S.Diag(Attr.getLoc(), diag::ext_cxx1z_attr) << Attr.getName();
 
   D->addAttr(::new (S.Context) 
              WarnUnusedResultAttr(Attr.getRange(), S.Context,
@@ -5072,7 +5072,7 @@ static void handleDeprecatedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   if (!S.getLangOpts().CPlusPlus14)
     if (Attr.isCXX11Attribute() &&
         !(Attr.hasScope() && Attr.getScopeName()->isStr("gnu")))
-      S.Diag(Attr.getLoc(), diag::ext_deprecated_attr_is_a_cxx14_extension);
+      S.Diag(Attr.getLoc(), diag::ext_cxx14_attr) << Attr.getName();
 
   handleAttrWithMessage<DeprecatedAttr>(S, D, Attr);
 }
@@ -5234,8 +5234,13 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
 
   switch (Attr.getKind()) {
   default:
-    // Type attributes are handled elsewhere; silently move on.
-    assert(Attr.isTypeAttr() && "Non-type attribute not handled");
+    if (!Attr.isStmtAttr()) {
+      // Type attributes are handled elsewhere; silently move on.
+      assert(Attr.isTypeAttr() && "Non-type attribute not handled");
+      break;
+    }
+    S.Diag(Attr.getLoc(), diag::err_stmt_attribute_invalid_on_decl)
+        << Attr.getName() << D->getLocation();
     break;
   case AttributeList::AT_Interrupt:
     handleInterruptAttr(S, D, Attr);
diff --git a/clang/lib/Sema/SemaStmtAttr.cpp b/clang/lib/Sema/SemaStmtAttr.cpp
index 0279441ee20..c1c7e808dc3 100644
--- a/clang/lib/Sema/SemaStmtAttr.cpp
+++ b/clang/lib/Sema/SemaStmtAttr.cpp
@@ -25,9 +25,11 @@ using namespace sema;
 
 static Attr *handleFallThroughAttr(Sema &S, Stmt *St, const AttributeList &A,
                                    SourceRange Range) {
+  FallThroughAttr Attr(A.getRange(), S.Context,
+                       A.getAttributeSpellingListIndex());
   if (!isa<NullStmt>(St)) {
     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_wrong_target)
-        << St->getLocStart();
+        << Attr.getSpelling() << St->getLocStart();
     if (isa<SwitchCase>(St)) {
       SourceLocation L = S.getLocForEndOfToken(Range.getEnd());
       S.Diag(L, diag::note_fallthrough_insert_semi_fixit)
@@ -35,12 +37,20 @@ static Attr *handleFallThroughAttr(Sema &S, Stmt *St, const AttributeList &A,
     }
     return nullptr;
   }
-  if (S.getCurFunction()->SwitchStack.empty()) {
+  auto *FnScope = S.getCurFunction();
+  if (FnScope->SwitchStack.empty()) {
     S.Diag(A.getRange().getBegin(), diag::err_fallthrough_attr_outside_switch);
     return nullptr;
   }
-  return ::new (S.Context) FallThroughAttr(A.getRange(), S.Context,
-                                           A.getAttributeSpellingListIndex());
+
+  // If this is spelled as the standard C++1z attribute, but not in C++1z, warn
+  // about using it as an extension.
+  if (!S.getLangOpts().CPlusPlus1z && A.isCXX11Attribute() &&
+      !A.getScopeName())
+    S.Diag(A.getLoc(), diag::ext_cxx1z_attr) << A.getName();
+
+  FnScope->setHasFallthroughStmt();
+  return ::new (S.Context) auto(Attr);
 }
 
 static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const AttributeList &A,
@@ -266,7 +276,7 @@ static Attr *ProcessStmtAttribute(Sema &S, Stmt *St, const AttributeList &A,
   default:
     // if we're here, then we parsed a known attribute, but didn't recognize
     // it as a statement attribute => it is declaration attribute
-    S.Diag(A.getRange().getBegin(), diag::err_attribute_invalid_on_stmt)
+    S.Diag(A.getRange().getBegin(), diag::err_decl_attribute_invalid_on_stmt)
         << A.getName() << St->getLocStart();
     return nullptr;
   }