Add regression tests for diagnostic processing.

clang/test/3C/diag_verifier_fail.c

@@ -0,0 +1,15 @@
+// Test that the diagnostic verifier is functioning correctly in 3c, because if
+// it isn't, all the other regression tests that use the diagnostic verifier may
+// not be able to catch the problems they are supposed to catch.
+//
+// This is exactly the same as diag_verifier_pass.c except that the warning
+// message we expect is deliberately wrong, so the diagnostic verifier should
+// fail.
+
+// RUN: rm -rf %t*
+// RUN: not 3c -base-dir=%S -extra-arg="-Wno-everything" -verify -warn-root-cause %s -- 2>%t.stderr
+// RUN: grep -q "error: 'warning' diagnostics expected but not seen:" %t.stderr
+// RUN: grep -q "error: 'warning' diagnostics seen but not expected:" %t.stderr
+
+// Example warning borrowed from root_cause.c .
+void *x; // expected-warning {{Default oops* type}}

clang/test/3C/diag_verifier_pass.c

@@ -0,0 +1,15 @@
+// Test that the diagnostic verifier is functioning correctly in 3c, because if
+// it isn't, all the other regression tests that use the diagnostic verifier may
+// not be able to catch the problems they are supposed to catch. This goes with
+// diag_verifier_fail.c.
+//
+// If 3c correctly exits nonzero when there is an error diagnostic (as tested by
+// stdout_mode_write_other.c) and the diagnostic verifier is not active at all,
+// then we would expect all the tests with expected errors to actually report
+// those errors and fail, so diag_verifier_{pass,fail}.c only add coverage for
+// unusual problems with the diagnostic verifier that we haven't seen yet.
+
+// RUN: 3c -base-dir=%S -extra-arg="-Wno-everything" -verify -warn-root-cause %s --
+
+// Example warning borrowed from root_cause.c .
+void *x; // expected-warning {{Default void* type}}

clang/test/3C/stdout_mode_write_other.c

@@ -2,8 +2,16 @@
 // writing base_subdir_partial_defn.h is not restricted by the base dir, so we
 // reach the stdout mode restriction.
 
+// RUN: rm -rf %t*
 // RUN: 3c -base-dir=%S -addcr -verify %s --
 
+// Same as above, except instead of using the diagnostic verifier, manually test
+// that 3c exits nonzero and prints the error to stderr. This tests that 3c
+// handles diagnostics properly.
+//
+// RUN: not 3c -base-dir=%S -addcr %s -- 2>%t.stderr
+// RUN: grep -q 'error: 3C generated changes to this file, which is under the base dir but is not the main file and thus cannot be written in stdout mode' %t.stderr
+
 // expected-error@base_subdir_partial_defn.h:1 {{3C generated changes to this file, which is under the base dir but is not the main file and thus cannot be written in stdout mode}}
 // expected-note@*:* {{-dump-unwritable-changes}}
 // expected-note@*:* {{-allow-unwritable-changes}}