Fix the diagnostic verifier, plus a few other fixes. (#598)

* Reverse name of 3c -disccty option to reflect what it actually does.

By default, 3c adds the -f3c-tool compiler option to disable the Checked
C type checker. 3c's -disccty option (apparently an abbreviation for
"disable Checked C type checker") made 3c _not_ pass -f3c-tool, hence
leaving the type checker _enabled_. 3C's internal flag variable,
DisableCCTypeChecker, was also backwards, though interestingly, the
`3c -help` text was correct ("Do not disable checked c type checker").

This commit renames -disccty to -enccty and renames DisableCCTypeChecker
to EnableCCTypeChecker. We take the opportunity to further improve the
`3c -help` text too.

* Completely remove the old `3c -verify` option.

Now that 3C only runs one compiler "invocation" per translation unit,
with the new diagnostic verifier implementation, callers will be able to
just use the `-Xclang -verify` compiler option. And given that we may
want to use other diagnostic verifier options (e.g., `-verify=PREFIX` or
`-verify-ignore-unexpected`), let's standardize on using the original
compiler options rather than trying to define `3c` options wrapping all
of them.

* Switch from ClangTool::buildASTs to a custom _3CASTBuilderAction.

Replace the existing ArgumentsAdjusters with modifications to the option
data structures in _3CASTBuilderAction. More will be added to
_3CASTBuilderAction in the subsequent commits.

Fixes #536.

* Canonicalize -I directory paths in _3CASTBuilderAction.

This works per translation unit, so hopefully it is a complete and
correct fix to #515 that benefits all callers of 3C.

Remove the previous crude workaround from convert_project.

Fixes #515.

* Make diagnostic verification work after the redesign of #488.

Re-enable diagnostic verification in regression tests where it still
succeeds. It remains disabled in some tests in which failures were
introduced while it was disabled; #609 is for that.

Fixes #503.

* Migrate the difftypes* tests to the diagnostic verifier.

This feels a little cleaner than manually scanning the stderr and lets
us check the diagnostics more precisely, for what that's worth. We
couldn't do this before #488 both because 3C exited before the
diagnostics could be verified and because 3C didn't support custom
verify prefixes. #488 solved the first problem, and this PR solves the
second.

* Document diagnostic verification in 3C's CONTRIBUTING.md.

Author: mattmccutchen-cci

clang/docs/checkedc/3C/CONTRIBUTING.md

@@ -94,6 +94,58 @@ in subdirectories, so `*.c` will not pick up all of them; instead you
 can use `llvm-lit -vv .` to specify all test files under the current
 directory.
 
+### Diagnostic verification
+
+3C supports the standard Clang diagnostic verifier
+([`VerifyDiagnosticConsumer`](https://clang.llvm.org/doxygen/classclang_1_1VerifyDiagnosticConsumer.html#details))
+for testing errors and warnings reported by 3C via its main `DiagnosticsEngine`.
+(Some 3C errors and warnings are reported via other means and cannot be tested
+this way; the best solution we have for them right now is to `grep` the stderr
+of 3C.) Diagnostic verification can be enabled via the usual `-Xclang -verify`
+compiler option; other diagnostic verification options (`-Xclang
+-verify=PREFIX`, etc.) should also work as normal. These must be passed as
+_compiler_ options, not `3c` options; for example, if you are using `--` on the
+`3c` command line, these options must be passed _after_ the `--`.
+
+Some notes about diagnostic verification in the context of 3C:
+
+* Parsing of the source files uses some of the compiler logic and thus may
+  generate compiler warnings, just as if you ran `clang` on the code. These are
+  sent to the diagnostic verifier along with diagnostics generated by 3C's
+  analysis. If you find it distracting to have to include the compiler warnings
+  in the set of expected diagnostics for a test, you can turn them off via the
+  `-Wno-everything` compiler option (which does not affect diagnostics generated
+  by 3C's analysis).
+
+* The `3c` tool works in several passes, where each pass runs on all translation
+  units: first `3c` parses the source files, then it runs several passes of
+  analysis. If a pass encounters at least one error, `3c` exits at the end of
+  that pass. Diagnostic verification does not change the _point_ at which `3c`
+  exits, but it changes the exit _code_ to indicate the result of verification
+  rather than the presence of errors. The verification includes the diagnostics
+  from all passes up to the point at which `3c` exits (i.e., the same
+  diagnostics that would be displayed if verification were not used). However,
+  an error that doesn't go via the main `DiagnosticsEngine` will cause an
+  unsuccessful exit code regardless of diagnostic verification. (This is
+  typically the behavior you want for a test.)
+
+* Diagnostic verification is independent for each translation unit, so in tests
+  with multiple translation units, you'll have to be careful that preprocessing
+  of each translation unit sees the correct set of `expected-*` directives for
+  the diagnostics generated for that translation unit (or an
+  `expected-no-diagnostics` directive if that translation unit generates no
+  diagnostics, even if other translation units do generate diagnostics). Be
+  warned that since which translation unit generated a given diagnostic isn't
+  visible to a normal user, we don't put much work into coming up with sensible
+  rules for this, but it should at least be deterministic for testing.
+
+Note that some 3C tests use diagnostic verification on calls to `clang` rather
+than `3c`, so if you see `expected-*` directives in a test, you can look at the
+`RUN` commands to see which command has `-Xclang -verify` and is using the
+directives. If you want to verify diagnostics of more than one `RUN` command in
+the same test, you can use different directive prefixes (`-Xclang
+-verify=PREFIX`).
+
 ## Coding guidelines
 
 Please follow [LLVM coding

clang/include/clang/3C/3C.h

@@ -57,7 +57,7 @@ struct _3COptions {
 
   bool AddCheckedRegions;
 
-  bool DisableCCTypeChecker;
+  bool EnableCCTypeChecker;
 
   bool WarnRootCause;
 
@@ -68,11 +68,6 @@ struct _3COptions {
   bool ForceItypes;
 #endif
 
-  // Currently applies only to the rewriting phase (because it is the only phase
-  // that generates diagnostics, except for the declaration merging diagnostics
-  // that are currently fatal) and uses the default "expected" prefix.
-  bool VerifyDiagnosticOutput;
-
   bool DumpUnwritableChanges;
   bool AllowUnwritableChanges;
 
@@ -104,6 +99,8 @@ class _3CInterface {
          const std::vector<std::string> &SourceFileList,
          clang::tooling::CompilationDatabase *CompDB);
 
+  ~_3CInterface();
+
   // Call clang to provide the data
   bool parseASTs();
 
@@ -141,10 +138,25 @@ class _3CInterface {
   // Dump all stats related to performance.
   bool dumpStats();
 
+  // Determine the exit code that the `3c` tool should exit with after the last
+  // 3C stage, considering diagnostic verification. Must be called exactly once
+  // before the _3CInterface is destructed (unless construction failed).
+  int determineExitCode();
+
 private:
   _3CInterface(const struct _3COptions &CCopt,
                const std::vector<std::string> &SourceFileList,
-               clang::tooling::CompilationDatabase *CompDB, bool &Failed);
+               clang::tooling::CompilationDatabase *CompDB);
+
+  bool ConstructionFailed = false;
+  bool DeterminedExitCode = false;
+
+  bool HadNonDiagnosticError = false;
+
+  // Determine whether 3C can continue to the next stage of processing. Checks
+  // HadNonDiagnosticError and error diagnostics but ignores diagnostic
+  // verification.
+  bool isSuccessfulSoFar();
 
   // saved ASTs
   std::vector< std::unique_ptr< ASTUnit >> ASTs;