Disallow -warnings-as-errors in tidy_flags

* Also remove the undocumented complicated
  experiment to overwrite local warnings-as-errors.

Bug: 229801437
Test: WITH_TIDY=1 make; make tidy-soong_subset
Change-Id: I2fb32146b4685ab9f5198724c15c303f799b7a14

cc/tidy_test.go

@@ -22,6 +22,76 @@ import (
 	"android/soong/android"
 )
 
+func TestTidyFlagsWarningsAsErrors(t *testing.T) {
+	// The "tidy_flags" property should not contain -warnings-as-errors.
+	testCases := []struct {
+		libName, bp string
+		errorMsg    string   // a negative test; must have error message
+		flags       []string // must have substrings in tidyFlags
+		noFlags     []string // must not have substrings in tidyFlags
+	}{
+		{
+			"libfoo1",
+			`cc_library_shared { // no warnings-as-errors, good tidy_flags
+			  name: "libfoo1",
+			  srcs: ["foo.c"],
+              tidy_flags: ["-header-filter=dir1/"],
+		    }`,
+			"",
+			[]string{"-header-filter=dir1/"},
+			[]string{"-warnings-as-errors"},
+		},
+		{
+			"libfoo2",
+			`cc_library_shared { // good use of tidy_checks_as_errors
+			  name: "libfoo2",
+			  srcs: ["foo.c"],
+			  tidy_checks_as_errors: ["xyz-*", "abc"],
+              tidy_flags: ["-header-filter=dir2/"],
+		    }`,
+			"",
+			[]string{"-header-filter=dir2/", "-warnings-as-errors='xyz-*',abc"},
+			[]string{},
+		},
+		{
+			"libfoo3",
+			`cc_library_shared { // bad use of -warnings-as-errors in tidy_flags
+			  name: "libfoo3",
+			  srcs: ["foo.c"],
+              tidy_flags: [
+                "-header-filters=.*",
+			    "-warnings-as-errors=xyz-*",
+              ],
+		    }`,
+			`module "libfoo3" .*: tidy_flags: should not contain -warnings-as-errors,` +
+				` use tidy_checks_as_errors instead`,
+			[]string{},
+			[]string{},
+		},
+	}
+	for _, test := range testCases {
+		if test.errorMsg != "" {
+			testCcError(t, test.errorMsg, test.bp)
+			continue
+		}
+		variant := "android_arm64_armv8-a_shared"
+		ctx := testCc(t, test.bp)
+		t.Run("caseTidyFlags", func(t *testing.T) {
+			flags := ctx.ModuleForTests(test.libName, variant).Rule("clangTidy").Args["tidyFlags"]
+			for _, flag := range test.flags {
+				if !strings.Contains(flags, flag) {
+					t.Errorf("tidyFlags for %s does not contain %s.", test.libName, flag)
+				}
+			}
+			for _, flag := range test.noFlags {
+				if strings.Contains(flags, flag) {
+					t.Errorf("tidyFlags for %s should not contain %s.", test.libName, flag)
+				}
+			}
+		})
+	}
+}
+
 func TestTidyChecks(t *testing.T) {
 	// The "tidy_checks" property defines additional checks appended
 	// to global default. But there are some checks disabled after