[clang] Add getUnsignedPointerDiffType method

[alexander-shaposhnikov]

Summary

C11 standard refers to the unsigned counterpart of the type ptrdiff_t
in the paragraph 7.21.6.1p7 where it defines the format specifier %tu.
In Clang (in PrintfFormatString.cpp, lines 508-510) there is a FIXME for this case,
in particular, right now Clang doesn't diagnose %tu issues at all, i.e.
it doesn't emit any warnings on the code printf("%tu", 3.14).
In this diff we add a method getUnsignedPointerDiffType for getting the corresponding type
similarly to how it's already done in the other analogous cases (size_t, ssize_t, ptrdiff_t etc)
and fix -Wformat diagnostics for %tu plus the emitted fix-it as well.

[alexander-shaposhnikov]

fix typo

[aaron.ballman]

The code for printf diagnostics + new tests are supposed to be added by a separate diff.

I think you should combine that diff and this one into a single patch, otherwise this patch is untestable.

include/clang/AST/ASTContext.h

1492–1493

Wrap the comment, and you might want to refer to C11 7.21.6.1p7 as a justification for why this is needed.

[alexander-shaposhnikov]

Address the comments

[aaron.ballman]

test/FixIt/format.m

256 ↗

(On Diff #116894)

Can you add some positive tests that show "%t" and "%tu" working properly without warnings?

[alexander-shaposhnikov]

Add positive tests

[aaron.ballman]

LGTM!

include/clang/AST/ASTContext.h

public:
   /// \brief Return a type compatible with "uintptr_t" (C99 7.18.1.4),
   /// as defined by the target.
   QualType getUIntPtrType() const;
 
   /// \brief Return the unique type for "ptrdiff_t" (C99 7.17) defined in
   /// <stddef.h>. Pointer - pointer requires this (C99 6.5.6p9).
   QualType getPointerDiffType() const;
 
+  /// \brief Return the unique unsigned counterpart of 
+  /// "ptrdiff_t" integer type.
+  QualType getUnsignedPointerDiffType() const;
+
   /// \brief Return the unique type for "pid_t" defined in
   /// <sys/types.h>. We need this to compute the correct type for vfork().
   QualType getProcessIDType() const;
 
   /// \brief Return the C structure type used to represent constant CFStrings.
   QualType getCFConstantStringType() const;
 
   /// \brief Returns the C struct type for objc_super

include/clang/Basic/TargetInfo.h

public:
   }
   IntType getIntMaxType() const { return IntMaxType; }
   IntType getUIntMaxType() const {
     return getCorrespondingUnsignedType(IntMaxType);
   }
   IntType getPtrDiffType(unsigned AddrSpace) const {
     return AddrSpace == 0 ? PtrDiffType : getPtrDiffTypeV(AddrSpace);
   }
+  IntType getUnsignedPtrDiffType(unsigned AddrSpace) const {
+    return getCorrespondingUnsignedType(getPtrDiffType(AddrSpace));
+  }
   IntType getIntPtrType() const { return IntPtrType; }
   IntType getUIntPtrType() const {
     return getCorrespondingUnsignedType(IntPtrType);
   }
   IntType getWCharType() const { return WCharType; }
   IntType getWIntType() const { return WIntType; }
   IntType getChar16Type() const { return Char16Type; }
   IntType getChar32Type() const { return Char32Type; }

lib/AST/ASTContext.cpp

 }
 
 /// getPointerDiffType - Return the unique type for "ptrdiff_t" (C99 7.17)
 /// defined in <stddef.h>. Pointer - pointer requires this (C99 6.5.6p9).
 QualType ASTContext::getPointerDiffType() const {
   return getFromTargetType(Target->getPtrDiffType(0));
 }
 
+/// getUnsignedPointerDiffType - Return the unique unsigned counterpart of
+/// "ptrdiff_t" integer type.
+QualType ASTContext::getUnsignedPointerDiffType() const {
+  return getFromTargetType(Target->getUnsignedPtrDiffType(0));
+}
+
 /// \brief Return the unique type for "pid_t" defined in
 /// <sys/types.h>. We need this to compute the correct type for vfork().
 QualType ASTContext::getProcessIDType() const {
   return getFromTargetType(Target->getProcessIDType());
 }
 
 //===----------------------------------------------------------------------===//
 //                              Type Operators