cmd/go: invalidate cached test results if env vars or files change

When we write a cached test result, we now also write a log of the
environment variables and files inspected by the test run,
along with a hash of their content. Before reusing a cached test result,
we recompute the hash of the content specified by the log, and only
use the result if that content has not changed.

This makes test caching behave correctly for tests that consult
environment variables or stat or read files or directories.

Fixes #22593.

Change-Id: I8608798e73c90e0c1911a38bf7e03e1232d784dc
Reviewed-on: https://go-review.googlesource.com/81895
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 91 insertions, 2 deletions

diff --git a/src/testing/internal/testdeps/deps.go b/src/testing/internal/testdeps/deps.go
index 042f69614e..8c0b3fded1 100644
--- a/src/testing/internal/testdeps/deps.go
+++ b/src/testing/internal/testdeps/deps.go
@@ -11,9 +11,13 @@
 package testdeps
 
 import (
+	"bufio"
+	"internal/testlog"
 	"io"
 	"regexp"
 	"runtime/pprof"
+	"strings"
+	"sync"
 )
 
 // TestDeps is an implementation of the testing.testDeps interface,
@@ -56,3 +60,61 @@ var ImportPath string
 func (TestDeps) ImportPath() string {
 	return ImportPath
 }
+
+// testLog implements testlog.Interface, logging actions by package os.
+type testLog struct {
+	mu sync.Mutex
+	w  *bufio.Writer
+}
+
+func (l *testLog) Getenv(key string) {
+	l.add("getenv", key)
+}
+
+func (l *testLog) Open(name string) {
+	l.add("open", name)
+}
+
+func (l *testLog) Stat(name string) {
+	l.add("stat", name)
+}
+
+func (l *testLog) Chdir(name string) {
+	l.add("chdir", name)
+}
+
+// add adds the (op, name) pair to the test log.
+func (l *testLog) add(op, name string) {
+	if strings.Contains(name, "\n") || name == "" {
+		return
+	}
+
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	if l.w == nil {
+		return
+	}
+	l.w.WriteString(op)
+	l.w.WriteByte(' ')
+	l.w.WriteString(name)
+	l.w.WriteByte('\n')
+}
+
+var log testLog
+
+func (TestDeps) StartTestLog(w io.Writer) {
+	log.mu.Lock()
+	log.w = bufio.NewWriter(w)
+	log.w.WriteString("# test log\n") // known to cmd/go/internal/test/test.go
+	log.mu.Unlock()
+
+	testlog.SetLogger(&log)
+}
+
+func (TestDeps) StopTestLog() error {
+	log.mu.Lock()
+	defer log.mu.Unlock()
+	err := log.w.Flush()
+	log.w = nil
+	return err
+}
diff --git a/src/testing/testing.go b/src/testing/testing.go
index cddd475fd7..402780ad64 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -268,10 +268,12 @@ var (
 	timeout              = flag.Duration("test.timeout", 0, "panic test binary after duration `d` (default 0, timeout disabled)")
 	cpuListStr           = flag.String("test.cpu", "", "comma-separated `list` of cpu counts to run each test with")
 	parallel             = flag.Int("test.parallel", runtime.GOMAXPROCS(0), "run at most `n` tests in parallel")
+	testlog              = flag.String("test.testlogfile", "", "write test action log to `file` (for use only by cmd/go)")
 
 	haveExamples bool // are there examples?
 
-	cpuList []int
+	cpuList     []int
+	testlogFile *os.File
 
 	numFailed uint32 // number of test failures
 )
@@ -889,6 +891,8 @@ func (f matchStringOnly) StopCPUProfile()                             {}
 func (f matchStringOnly) WriteHeapProfile(w io.Writer) error          { return errMain }
 func (f matchStringOnly) WriteProfileTo(string, io.Writer, int) error { return errMain }
 func (f matchStringOnly) ImportPath() string                          { return "" }
+func (f matchStringOnly) StartTestLog(io.Writer)                      {}
+func (f matchStringOnly) StopTestLog() error                          { return errMain }
 
 // Main is an internal function, part of the implementation of the "go test" command.
 // It was exported because it is cross-package and predates "internal" packages.
@@ -916,12 +920,14 @@ type M struct {
 // The canonical implementation of this interface is
 // testing/internal/testdeps's TestDeps.
 type testDeps interface {
+	ImportPath() string
 	MatchString(pat, str string) (bool, error)
 	StartCPUProfile(io.Writer) error
 	StopCPUProfile()
+	StartTestLog(io.Writer)
+	StopTestLog() error
 	WriteHeapProfile(io.Writer) error
 	WriteProfileTo(string, io.Writer, int) error
-	ImportPath() string
 }
 
 // MainStart is meant for use by tests generated by 'go test'.
@@ -1100,6 +1106,17 @@ func (m *M) before() {
 		fmt.Fprintf(os.Stderr, "testing: cannot use -test.coverprofile because test binary was not built with coverage enabled\n")
 		os.Exit(2)
 	}
+	if *testlog != "" {
+		// Note: Not using toOutputDir.
+		// This file is for use by cmd/go, not users.
+		f, err := os.Create(*testlog)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: %s\n", err)
+			os.Exit(2)
+		}
+		m.deps.StartTestLog(f)
+		testlogFile = f
+	}
 }
 
 // after runs after all testing.
@@ -1110,6 +1127,16 @@ func (m *M) after() {
 }
 
 func (m *M) writeProfiles() {
+	if *testlog != "" {
+		if err := m.deps.StopTestLog(); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
+			os.Exit(2)
+		}
+		if err := testlogFile.Close(); err != nil {
+			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *testlog, err)
+			os.Exit(2)
+		}
+	}
 	if *cpuProfile != "" {
 		m.deps.StopCPUProfile() // flushes profile to disk
 	}