cmd/go: convert TestCacheVet to a script

This test was failing when GOROOT was read-only.

(I'm not sure why that was the case, but it's simpler to convert to to
a script than to try to debug the non-script test.)

Updates #28387

Change-Id: I9943e28d990e5d8b01da10e70531f3ab99e319a7
Reviewed-on: https://go-review.googlesource.com/c/go/+/206897
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/go/go_test.go

@@ -5214,38 +5214,6 @@ func TestCacheCoverage(t *testing.T) {
 	tg.run("test", "-cover", "-short", "math", "strings")
 }
 
-func TestCacheVet(t *testing.T) {
-	skipIfGccgo(t, "gccgo has no standard packages")
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.parallel()
-
-	if strings.Contains(os.Getenv("GODEBUG"), "gocacheverify") {
-		t.Skip("GODEBUG gocacheverify")
-	}
-	if testing.Short() {
-		// In short mode, reuse cache.
-		// Test failures may be masked if the cache has just the right entries already
-		// (not a concern during all.bash, which runs in a clean cache).
-		if cfg.Getenv("GOCACHE") == "off" {
-			tooSlow(t)
-		}
-	} else {
-		tg.makeTempdir()
-		tg.setenv("GOCACHE", tg.path("cache"))
-	}
-
-	// Check that second vet reuses cgo-derived inputs.
-	// The first command could be build instead of vet,
-	// except that if the cache is empty and there's a net.a
-	// in GOROOT/pkg, the build will not bother to regenerate
-	// and cache the cgo outputs, whereas vet always will.
-	tg.run("vet", "os/user")
-	tg.run("vet", "-x", "os/user")
-	tg.grepStderrNot(`^(clang|gcc)`, "should not have run compiler")
-	tg.grepStderrNot(`[\\/]cgo `, "should not have run cgo")
-}
-
 func TestIssue22588(t *testing.T) {
 	// Don't get confused by stderr coming from tools.
 	tg := testgo(t)

src/cmd/go/script_test.go

@@ -292,6 +292,17 @@ Script:
 					}).(bool)
 					break
 				}
+				if strings.HasPrefix(cond.tag, "GODEBUG:") {
+					value := strings.TrimPrefix(cond.tag, "GODEBUG:")
+					parts := strings.Split(os.Getenv("GODEBUG"), ",")
+					for _, p := range parts {
+						if strings.TrimSpace(p) == value {
+							ok = true
+							break
+						}
+					}
+					break
+				}
 				if !imports.KnownArch[cond.tag] && !imports.KnownOS[cond.tag] && cond.tag != "gc" && cond.tag != "gccgo" {
 					ts.fatalf("unknown condition %q", cond.tag)
 				}

src/cmd/go/testdata/script/README

@@ -77,6 +77,7 @@ should only run when the condition is satisfied. The available conditions are:
    - [root] for os.Geteuid() == 0
    - [symlink] for testenv.HasSymlink()
    - [exec:prog] for whether prog is available for execution (found by exec.LookPath)
+   - [GODEBUG:value] for whether value is one of the comma-separated entries in the GODEBUG variable
 
 A condition can be negated: [!short] means to run the rest of the line
 when testing.Short() is false. Multiple conditions may be given for a single

src/cmd/go/testdata/script/cache_vet.txt

@@ -0,0 +1,22 @@
+env GO111MODULE=off
+
+[short] skip
+[GODEBUG:gocacheverify] skip
+[gccgo] skip  # gccgo has no standard packages
+
+# Start with a clean build cache:
+# test failures may be masked if the cache has just the right entries already.
+env GOCACHE=$WORK/cache
+
+# Run 'go vet os/user' once to warm up the cache.
+go vet os/user
+
+# Check that second vet reuses cgo-derived inputs.
+# The first command could be build instead of vet,
+# except that if the cache is empty and there's a net.a
+# in GOROOT/pkg, the build will not bother to regenerate
+# and cache the cgo outputs, whereas vet always will.
+
+go vet -x os/user
+! stderr '^(clang|gcc)'  # should not have run compiler
+! stderr '[\\/]cgo '     # should not have run cgo