testing: enable examples on js/wasm with non os.Pipe runExample

os.Pipe is not implemented on wasm/js so for that purpose use
a temporary file for js/wasm. This change creates two versions
of runExample:

* runExample verbatim that still uses os.Pipe for non js/wasm
* runExample that uses a temporary file

Also added a TODO to re-unify these function versions back into
example.go wasm/js gets an os.Pipe implementation.

Change-Id: I9f418a49b2c397e1667724c7442b7bbe8942225e
Reviewed-on: https://go-review.googlesource.com/c/go/+/165357
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/testing/example.go

@@ -6,7 +6,6 @@ package testing
 
 import (
 	"fmt"
-	"io"
 	"os"
 	"sort"
 	"strings"
@@ -56,68 +55,39 @@ func sortLines(output string) string {
 	return strings.Join(lines, "\n")
 }
 
-func runExample(eg InternalExample) (ok bool) {
-	if *chatty {
-		fmt.Printf("=== RUN   %s\n", eg.Name)
-	}
-
-	// Capture stdout.
-	stdout := os.Stdout
-	r, w, err := os.Pipe()
-	if err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
-	}
-	os.Stdout = w
-	outC := make(chan string)
-	go func() {
-		var buf strings.Builder
-		_, err := io.Copy(&buf, r)
-		r.Close()
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "testing: copying pipe: %v\n", err)
-			os.Exit(1)
-		}
-		outC <- buf.String()
-	}()
-
-	start := time.Now()
-	ok = true
-
-	// Clean up in a deferred call so we can recover if the example panics.
-	defer func() {
-		dstr := fmtDuration(time.Since(start))
-
-		// Close pipe, restore stdout, get output.
-		w.Close()
-		os.Stdout = stdout
-		out := <-outC
-
+// processRunResult computes a summary and status of the result of running an example test.
+// stdout is the captured output from stdout of the test.
+// recovered is the result of invoking recover after running the test, in case it panicked.
+//
+// If stdout doesn't match the expected output or if recovered is non-nil, it'll print the cause of failure to stdout.
+// If the test is chatty/verbose, it'll print a success message to stdout.
+// If recovered is non-nil, it'll panic with that value.
+func (eg *InternalExample) processRunResult(stdout string, timeSpent time.Duration, recovered interface{}) (passed bool) {
+	passed = true
+
+	dstr := fmtDuration(timeSpent)
 	var fail string
-		err := recover()
-		got := strings.TrimSpace(out)
+	got := strings.TrimSpace(stdout)
 	want := strings.TrimSpace(eg.Output)
 	if eg.Unordered {
-			if sortLines(got) != sortLines(want) && err == nil {
-				fail = fmt.Sprintf("got:\n%s\nwant (unordered):\n%s\n", out, eg.Output)
+		if sortLines(got) != sortLines(want) && recovered == nil {
+			fail = fmt.Sprintf("got:\n%s\nwant (unordered):\n%s\n", stdout, eg.Output)
 		}
 	} else {
-			if got != want && err == nil {
+		if got != want && recovered == nil {
 			fail = fmt.Sprintf("got:\n%s\nwant:\n%s\n", got, want)
 		}
 	}
-		if fail != "" || err != nil {
+	if fail != "" || recovered != nil {
 		fmt.Printf("--- FAIL: %s (%s)\n%s", eg.Name, dstr, fail)
-			ok = false
+		passed = false
 	} else if *chatty {
 		fmt.Printf("--- PASS: %s (%s)\n", eg.Name, dstr)
 	}
-		if err != nil {
-			panic(err)
+	if recovered != nil {
+		// Propagate the previously recovered result, by panicking.
+		panic(recovered)
 	}
-	}()
 
-	// Run example.
-	eg.F()
 	return
 }

src/testing/run_example.go

+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !js
+
+// TODO(@musiol, @odeke-em): re-unify this entire file back into
+// example.go when js/wasm gets an os.Pipe implementation
+// and no longer needs this separation.
+
+package testing
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"time"
+)
+
+func runExample(eg InternalExample) (ok bool) {
+	if *chatty {
+		fmt.Printf("=== RUN   %s\n", eg.Name)
+	}
+
+	// Capture stdout.
+	stdout := os.Stdout
+	r, w, err := os.Pipe()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	os.Stdout = w
+	outC := make(chan string)
+	go func() {
+		var buf strings.Builder
+		_, err := io.Copy(&buf, r)
+		r.Close()
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "testing: copying pipe: %v\n", err)
+			os.Exit(1)
+		}
+		outC <- buf.String()
+	}()
+
+	start := time.Now()
+
+	// Clean up in a deferred call so we can recover if the example panics.
+	defer func() {
+		timeSpent := time.Since(start)
+
+		// Close pipe, restore stdout, get output.
+		w.Close()
+		os.Stdout = stdout
+		out := <-outC
+
+		err := recover()
+		ok = eg.processRunResult(out, timeSpent, err)
+	}()
+
+	// Run example.
+	eg.F()
+	return
+}

src/testing/run_example_js.go

+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build js
+
+package testing
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"time"
+)
+
+// TODO(@musiol, @odeke-em): unify this code back into
+// example.go when js/wasm gets an os.Pipe implementation.
+func runExample(eg InternalExample) (ok bool) {
+	if *chatty {
+		fmt.Printf("=== RUN   %s\n", eg.Name)
+	}
+
+	// Capture stdout to temporary file. We're not using
+	// os.Pipe because it is not supported on js/wasm.
+	stdout := os.Stdout
+	f := createTempFile(eg.Name)
+	os.Stdout = f
+	start := time.Now()
+
+	// Clean up in a deferred call so we can recover if the example panics.
+	defer func() {
+		timeSpent := time.Since(start)
+
+		// Restore stdout, get output and remove temporary file.
+		os.Stdout = stdout
+		var buf strings.Builder
+		_, seekErr := f.Seek(0, os.SEEK_SET)
+		_, readErr := io.Copy(&buf, f)
+		out := buf.String()
+		f.Close()
+		os.Remove(f.Name())
+		if seekErr != nil {
+			fmt.Fprintf(os.Stderr, "testing: seek temp file: %v\n", seekErr)
+			os.Exit(1)
+		}
+		if readErr != nil {
+			fmt.Fprintf(os.Stderr, "testing: read temp file: %v\n", readErr)
+			os.Exit(1)
+		}
+
+		err := recover()
+		ok = eg.processRunResult(out, timeSpent, err)
+	}()
+
+	// Run example.
+	eg.F()
+	return
+}
+
+func createTempFile(exampleName string) *os.File {
+	for i := 0; ; i++ {
+		name := fmt.Sprintf("%s/go-example-stdout-%s-%d.txt", os.TempDir(), exampleName, i)
+		f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
+		if err != nil {
+			if os.IsExist(err) {
+				continue
+			}
+			fmt.Fprintf(os.Stderr, "testing: open temp file: %v\n", err)
+			os.Exit(1)
+		}
+		return f
+	}
+}