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.

clang/lib/3C/3C.cpp

@@ -119,6 +119,12 @@ class _3CDiagnosticConsumer : public DiagnosticConsumer {
 public:
   _3CDiagnosticConsumer(DiagnosticsEngine &Engine)
       : UnderlyingConsumer(Engine.takeClient()) {
+    // This code currently only supports the default LibTooling setup in which
+    // the ClangTool has no global DiagnosticConsumer, so
+    // CompilerInstance::createDiagnostics creates one owned by the
+    // DiagnosticsEngine. If we needed to support the case in which the
+    // DiagnosticConsumer isn't owned, we could use an "UnderlyingConsumerOwner"
+    // pattern like VerifyDiagnosticConsumer does.
     assert(UnderlyingConsumer);
   }
 
@@ -153,7 +159,17 @@ class _3CDiagnosticConsumer : public DiagnosticConsumer {
     return UnderlyingConsumer->getNumErrors() == 0;
   }
 
-  ~_3CDiagnosticConsumer() { assert(CurrentState == S_Done); }
+  ~_3CDiagnosticConsumer() {
+    // We considered asserting that the state is S_Done here, but if
+    // ASTUnit::LoadFromCompilerInvocation fails and returns null, the
+    // _3CDiagnosticConsumer may be destructed without reaching S_Done. However,
+    // even without such an assertion, we're still well protected against
+    // forgetting to finish verification and missing an error because if the
+    // ASTUnit is null, _3CInterface::parseASTs will record a "non-diagnostic
+    // error", while if the ASTUnit is non-null, it will get added to
+    // _3CInterface::ASTs and determineExitCode will call finish3CAnalysis. (And
+    // the _3CInterface destructor enforces that determineExitCode is called.)
+  }
 };
 
 // Based on LibTooling's ASTBuilderAction but does several custom things that we

clang/test/3C/difftypes1a.c

@@ -1,7 +1,13 @@
-//RUN: rm -rf %t*
-//RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1b.c -- 2>%t.stderr
-//RUN: grep -q "merging failed" %t.stderr
+// Since the RUN commands in difftypes1a.c and difftypes1b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command. Verification
+// is per translation unit, so the translation unit with no diagnostic needs
+// `expected-no-diagnostics`.
 
-// The desired behavior in this case is to fail, so other checks are omitted
+//RUN: rm -rf %t*
+//RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1b.c -- -Xclang -verify=ab-expected
 
+// ab-expected-no-diagnostics
+// ba-expected-error@+1 {{merging failed for 'foo'}}
 _Ptr<int> foo(int, char);

clang/test/3C/difftypes1b.c

@@ -1,7 +1,13 @@
-//RUN: rm -rf %t*
-//RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1a.c -- 2>%t.stderr
-//RUN: grep -q "merging failed" %t.stderr
+// Since the RUN commands in difftypes1a.c and difftypes1b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command. Verification
+// is per translation unit, so the translation unit with no diagnostic needs
+// `expected-no-diagnostics`.
 
-// The desired behavior in this case is to fail, so other checks are omitted
+//RUN: rm -rf %t*
+//RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes1a.c -- -Xclang -verify=ba-expected
 
+// ba-expected-no-diagnostics
+// ab-expected-error@+1 {{merging failed for 'foo'}}
 int *foo(int, char *);

clang/test/3C/difftypes2a.c

@@ -1,9 +1,17 @@
+// Since the RUN commands in difftypes2a.c and difftypes2b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command. Verification
+// is per translation unit, so the translation unit with no diagnostic needs
+// `expected-no-diagnostics`.
+
 // RUN: rm -rf %t*
-// RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2b.c -- 2>%t.stderr
-// RUN: grep -q "merging failed" %t.stderr
+// RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2b.c -- -Xclang -verify=ab-expected
 
 // The desired behavior in this case is to fail, so other checks are omitted
 
 // Test no body vs body
 
+// ab-expected-no-diagnostics
+// ba-expected-error@+1 {{merging failed for 'foo'}}
 void foo(char *x);

clang/test/3C/difftypes2b.c

@@ -1,11 +1,17 @@
-// RUN: rm -rf %t*
-// RUN: not 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2a.c -- 2>%t.stderr
-// RUN: grep -q "merging failed" %t.stderr
+// Since the RUN commands in difftypes2a.c and difftypes2b.c process the two
+// files in different orders and the location where the error is reported
+// depends on the order, we need to use a different diagnostic verification
+// prefix (and set of corresponding comments) for each RUN command. Verification
+// is per translation unit, so the translation unit with no diagnostic needs
+// `expected-no-diagnostics`.
 
-// The desired behavior in this case is to fail, so other checks are omitted
+// RUN: rm -rf %t*
+// RUN: 3c -base-dir=%S -output-dir=%t.checked %s %S/difftypes2a.c -- -Xclang -verify=ba-expected
 
 // Test body vs no body
 
+// ba-expected-no-diagnostics
+// ab-expected-error@+1 {{merging failed for 'foo'}}
 void foo(char **y) {
   // this is the body
 }