Implement -Wcast-qual, fixing #13772.

Many thanks to dblaikie for his advices and suggestions!

llvm-svn: 222568

clang/include/clang/Basic/DiagnosticGroups.td

@@ -60,7 +60,7 @@ def ExternCCompat : DiagGroup<"extern-c-compat">;
 def KeywordCompat : DiagGroup<"keyword-compat">;
 def GNUCaseRange : DiagGroup<"gnu-case-range">;
 def CastAlign : DiagGroup<"cast-align">;
-def : DiagGroup<"cast-qual">;
+def CastQual : DiagGroup<"cast-qual">;
 def : DiagGroup<"char-align">;
 def Comment : DiagGroup<"comment">;
 def GNUComplexInteger : DiagGroup<"gnu-complex-integer">;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6115,6 +6115,11 @@ def warn_zero_size_struct_union_compat : Warning<"%select{|empty }0"
 def warn_zero_size_struct_union_in_extern_c : Warning<"%select{|empty }0"
   "%select{struct|union}1 has size 0 in C, %select{size 1|non-zero size}2 in C++">,
   InGroup<ExternCCompat>;
+def warn_cast_qual : Warning<"cast from %0 to %1 drops %select{const and "
+  "volatile qualifiers|const qualifier|volatile qualifier}2">,
+  InGroup<CastQual>, DefaultIgnore;
+def warn_cast_qual2 : Warning<"cast from %0 to %1 must have all intermediate "
+  "pointers const qualified to be safe">, InGroup<CastQual>, DefaultIgnore;
 } // End of general sema category.
 
 // inline asm.

clang/lib/Sema/SemaCast.cpp

@@ -142,9 +142,6 @@ namespace {
   };
 }
 
-static bool CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
-                               bool CheckCVR, bool CheckObjCLifetime);
-
 // The Try functions attempt a specific way of casting. If they succeed, they
 // return TC_Success. If their way of casting is not appropriate for the given
 // arguments, they return TC_NotApplicable and *may* set diag to a diagnostic
@@ -462,7 +459,10 @@ static bool UnwrapDissimilarPointerTypes(QualType& T1, QualType& T2) {
 /// \param CheckObjCLifetime Whether to check Objective-C lifetime qualifiers.
 static bool
 CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
-                   bool CheckCVR, bool CheckObjCLifetime) {
+                   bool CheckCVR, bool CheckObjCLifetime,
+                   QualType *TheOffendingSrcType = nullptr,
+                   QualType *TheOffendingDestType = nullptr,
+                   Qualifiers *CastAwayQualifiers = nullptr) {
   // If the only checking we care about is for Objective-C lifetime qualifiers,
   // and we're not in ARC mode, there's nothing to check.
   if (!CheckCVR && CheckObjCLifetime && 
@@ -487,6 +487,8 @@ CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
   // Find the qualifiers. We only care about cvr-qualifiers for the 
   // purpose of this check, because other qualifiers (address spaces, 
   // Objective-C GC, etc.) are part of the type's identity.
+  QualType PrevUnwrappedSrcType = UnwrappedSrcType;
+  QualType PrevUnwrappedDestType = UnwrappedDestType;
   while (UnwrapDissimilarPointerTypes(UnwrappedSrcType, UnwrappedDestType)) {
     // Determine the relevant qualifiers at this level.
     Qualifiers SrcQuals, DestQuals;
@@ -497,6 +499,13 @@ CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
     if (CheckCVR) {
       RetainedSrcQuals.setCVRQualifiers(SrcQuals.getCVRQualifiers());
       RetainedDestQuals.setCVRQualifiers(DestQuals.getCVRQualifiers());
+
+      if (RetainedSrcQuals != RetainedDestQuals && TheOffendingSrcType &&
+          TheOffendingDestType && CastAwayQualifiers) {
+        *TheOffendingSrcType = PrevUnwrappedSrcType;
+        *TheOffendingDestType = PrevUnwrappedDestType;
+        *CastAwayQualifiers = RetainedSrcQuals - RetainedDestQuals;
+      }
     }
     
     if (CheckObjCLifetime &&
@@ -505,6 +514,9 @@ CastsAwayConstness(Sema &Self, QualType SrcType, QualType DestType,
     
     cv1.push_back(RetainedSrcQuals);
     cv2.push_back(RetainedDestQuals);
+
+    PrevUnwrappedSrcType = UnwrappedSrcType;
+    PrevUnwrappedDestType = UnwrappedDestType;
   }
   if (cv1.empty())
     return false;
@@ -2371,6 +2383,30 @@ void CastOperation::CheckCStyleCast() {
 
   if (Kind == CK_BitCast)
     checkCastAlign();
+
+  // -Wcast-qual
+  QualType TheOffendingSrcType, TheOffendingDestType;
+  Qualifiers CastAwayQualifiers;
+  if (SrcType->isAnyPointerType() && DestType->isAnyPointerType() &&
+      CastsAwayConstness(Self, SrcType, DestType, true, false,
+                         &TheOffendingSrcType, &TheOffendingDestType,
+                         &CastAwayQualifiers)) {
+    int qualifiers = -1;
+    if (CastAwayQualifiers.hasConst() && CastAwayQualifiers.hasVolatile()) {
+      qualifiers = 0;
+    } else if (CastAwayQualifiers.hasConst()) {
+      qualifiers = 1;
+    } else if (CastAwayQualifiers.hasVolatile()) {
+      qualifiers = 2;
+    }
+    // This is a variant of int **x; const int **y = (const int **)x;
+    if (qualifiers == -1)
+      Self.Diag(SrcExpr.get()->getLocStart(), diag::warn_cast_qual2) <<
+        SrcType << DestType;
+    else
+      Self.Diag(SrcExpr.get()->getLocStart(), diag::warn_cast_qual) <<
+        TheOffendingSrcType << TheOffendingDestType << qualifiers;
+  }
 }
 
 ExprResult Sema::BuildCStyleCastExpr(SourceLocation LPLoc,

clang/test/Sema/warn-cast-qual.c

@@ -0,0 +1,29 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -fsyntax-only -Wcast-qual -verify %s
+
+#include <stdint.h>
+
+void foo() {
+  const char * const ptr = 0;
+  const char * const *ptrptr = 0;
+  char *y = (char *)ptr;	// expected-warning {{cast from 'const char *' to 'char *' drops const qualifier}}
+  char **y1 = (char **)ptrptr;	// expected-warning {{cast from 'const char *const' to 'char *' drops const qualifier}}
+  const char **y2 = (const char **)ptrptr;	// expected-warning {{cast from 'const char *const *' to 'const char **' drops const qualifier}}
+
+  char *z = (char *)(uintptr_t)(const void *)ptr;	// no warning
+  char *z1 = (char *)(const void *)ptr;	// expected-warning {{cast from 'const void *' to 'char *' drops const qualifier}}
+
+  volatile char *vol = 0;
+  char *vol2 = (char *)vol; // expected-warning {{cast from 'volatile char *' to 'char *' drops volatile qualifier}}
+  const volatile char *volc = 0;
+  char *volc2 = (char *)volc; // expected-warning {{cast from 'const volatile char *' to 'char *' drops const and volatile qualifiers}}
+
+  int **intptrptr;
+  const int **intptrptrc = (const int **)intptrptr; // expected-warning {{cast from 'int **' to 'const int **' must have all intermediate pointers const qualified}}
+  volatile int **intptrptrv = (volatile int **)intptrptr; // expected-warning {{cast from 'int **' to 'volatile int **' must have all intermediate pointers const qualified}}
+
+  int *intptr;
+  const int *intptrc = (const int *)intptr;    // no warning
+
+  const char **charptrptrc;
+  char **charptrptr = (char **)charptrptrc; // expected-warning {{cast from 'const char *' to 'char *' drops const qualifier}}
+}