[PATCH] D15314: Fix a bug in unavailable checking

[Manman Ren via cfe-commits]

manmanren created this revision.
manmanren added reviewers: rjmccall, rsmith.
manmanren added a subscriber: cfe-commits.

The issue —————————————
Given the following test case, we don’t emit any message, and will silently ignore the variable "foo2", with a release compiler; we will get an assertion failure with an assert compiler.
typedef struct {
  const char *name;
  id field;
} Test9;

extern void doSomething(Test9 arg);
void test9() {
    Test9 foo2 = {0, 0};
    doSomething(foo2);
}

The root cause —————————————
Back in r140457 we gave InitListChecker a verification-only mode, and will use CanUseDecl instead of DiagnoseUseOfDecl for verification-only mode.
These two functions handle unavailable issues differently:
In Sema::CanUseDecl, we say the decl is invalid with the following condition
  if (D->getAvailability() == AR_Unavailable &&
      cast<Decl>(CurContext)->getAvailability() != AR_Unavailable)
In Sema::DiagnoseUseOfDecl, we say the decl is usable by ignoring the return code of DiagnoseAvailabilityOfDecl

So with an assert build, we will hit an assertion in diagnoseListInit
  assert(DiagnoseInitList.HadError() &&
         "Inconsistent init list check result.");

The question is how to make the two consistent, should we follow what is implemented in CanUseDecl or DiagnoseUseOfDecl?
If we follow what is implemented in CanUseDecl and treat Decls with unavailable issues as invalid, the variable decl of “foo2” will be marked as invalid.
Since unavailable checking is processed in delayed diagnostics (r197627), we will silently ignore the diagnostics when we find out that the variable decl is invalid.

In Sema::PopParsingDeclaration
      switch (diag.Kind) {
      case DelayedDiagnostic::Deprecation:
      case DelayedDiagnostic::Unavailable:
        // Don't bother giving deprecation/unavailable diagnostics if
        // the decl is invalid.
        if (!decl->isInvalidDecl())
          handleDelayedAvailabilityCheck(*this, diag, decl);

The proposed fix ———————————————
It seems that for overload resolution, we want to say decls with unavailable issues are invalid; but for everything else, we should say they are valid but
emit diagnostics. For this, we can add another flag “UnavailableCheck” for the verification-only mode. Depending on the value of the flag, CanUseDecl
can return different values for unavailable issues.

Feedback is appreciated. Any other suggestion is welcome.

Cheers,
Manman

http://reviews.llvm.org/D15314

Files:
  include/clang/Sema/Initialization.h
  include/clang/Sema/Sema.h
  lib/Sema/SemaDecl.cpp
  lib/Sema/SemaExpr.cpp
  lib/Sema/SemaInit.cpp
  test/SemaObjC/Inputs/arc-system-header.h
  test/SemaObjC/arc-system-header.m

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