internal/testenv: skip tests that need export data for std if 'go too…

…l compile' does not exist

Now that .a files are no longer being preinstalled for
standard-library packages (#47257), tests that require the export data
from those files must have access to 'go list -export' in order to
generate and load export data from the Go build cache.

`go list -export` does not work without a Go compiler, so assume that
tests that need the 'go' command also need the compiler.

This may cause the tests currently failing on the android-.*-emu
builders to instead be skipped, since the test harness does not copy
the compiler to the execution environment.

For golang/go#47257.

Change-Id: Ie82ab09ac8165a01fc1d3a083b1e86226efc469d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/451597
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>

internal/testenv/testenv.go

@@ -94,6 +94,23 @@ func hasTool(tool string) error {
 			GOROOT := strings.TrimSpace(string(out))
 			if GOROOT != runtime.GOROOT() {
 				checkGoGoroot.err = fmt.Errorf("'go env GOROOT' does not match runtime.GOROOT:\n\tgo env: %s\n\tGOROOT: %s", GOROOT, runtime.GOROOT())
+				return
+			}
+
+			// Also ensure that that GOROOT includes a compiler: 'go' commands
+			// don't in general work without it, and some builders
+			// (such as android-amd64-emu) seem to lack it in the test environment.
+			cmd := exec.Command(tool, "tool", "-n", "compile")
+			stderr := new(bytes.Buffer)
+			stderr.Write([]byte("\n"))
+			cmd.Stderr = stderr
+			out, err = cmd.Output()
+			if err != nil {
+				checkGoGoroot.err = fmt.Errorf("%v: %v%s", cmd, err, stderr)
+				return
+			}
+			if _, err := os.Stat(string(bytes.TrimSpace(out))); err != nil {
+				checkGoGoroot.err = err
 			}
 		})
 		if checkGoGoroot.err != nil {