cmd/cover: add test for HTML output

This adds a case for what was fixed in 4fe688c to prevent regression;
a follow-on change will address #25767.

Change-Id: Iced8cc10e2993ef7caf7e9c59ffbc7147d78ddd7
Reviewed-on: https://go-review.googlesource.com/116975
Run-TryBot: David Symonds <dsymonds@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/cover/cover_test.go

@@ -5,6 +5,7 @@
 package main_test
 
 import (
+	"bufio"
 	"bytes"
 	"flag"
 	"fmt"
@@ -17,6 +18,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strings"
 	"testing"
 )
@@ -36,6 +38,12 @@ var (
 	coverInput   = filepath.Join(testdata, "test_line.go")
 	coverOutput  = filepath.Join(testdata, "test_cover.go")
 	coverProfile = filepath.Join(testdata, "profile.cov")
+
+	// The HTML test files are in a separate directory
+	// so they are a complete package.
+	htmlProfile = filepath.Join(testdata, "html", "html.cov")
+	htmlHTML    = filepath.Join(testdata, "html", "html.html")
+	htmlGolden  = filepath.Join(testdata, "html", "html.golden")
 )
 
 var debug = flag.Bool("debug", false, "keep rewritten files for debugging")
@@ -256,6 +264,57 @@ func TestCoverFunc(t *testing.T) {
 	}
 }
 
+// Check that cover produces correct HTML.
+// Issue #25767.
+func TestCoverHTML(t *testing.T) {
+	if _, err := exec.LookPath("diff"); err != nil {
+		t.Skipf("skip test on %s: diff command is required", runtime.GOOS)
+	}
+	testenv.MustHaveGoBuild(t)
+	if !*debug {
+		defer os.Remove(testcover)
+		defer os.Remove(htmlProfile)
+		defer os.Remove(htmlHTML)
+	}
+	// go build -o testcover
+	cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", testcover)
+	run(cmd, t)
+	// go test -coverprofile testdata/html/html.cov cmd/cover/testdata/html
+	cmd = exec.Command(testenv.GoToolPath(t), "test", "-coverprofile", htmlProfile, "cmd/cover/testdata/html")
+	run(cmd, t)
+	// ./testcover -html testdata/html/html.cov -o testdata/html/html.html
+	cmd = exec.Command(testcover, "-html", htmlProfile, "-o", htmlHTML)
+	run(cmd, t)
+
+	// Extract the parts of the HTML with comment markers,
+	// and compare against a golden file.
+	entireHTML, err := ioutil.ReadFile(htmlHTML)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var out bytes.Buffer
+	scan := bufio.NewScanner(bytes.NewReader(entireHTML))
+	in := false
+	for scan.Scan() {
+		line := scan.Text()
+		if strings.Contains(line, "// START") {
+			in = true
+		}
+		if in {
+			fmt.Fprintln(&out, line)
+		}
+		if strings.Contains(line, "// END") {
+			in = false
+		}
+	}
+	if err := ioutil.WriteFile(htmlHTML, out.Bytes(), 0644); err != nil {
+		t.Fatal(err)
+	}
+	// diff -ud testdata/html/html.html testdata/html/html.golden
+	cmd = exec.Command("diff", "-udw", htmlHTML, htmlGolden)
+	run(cmd, t)
+}
+
 func run(c *exec.Cmd, t *testing.T) {
 	t.Helper()
 	c.Stdout = os.Stdout

src/cmd/cover/testdata/html/html.go

@@ -0,0 +1,18 @@
+package html
+
+// This file is tested by html_test.go.
+// The comments below are markers for extracting the annotated source
+// from the HTML output.
+
+// This is a regression test for incorrect sorting of boundaries
+// that coincide, specifically for empty select clauses.
+// START f
+func f() {
+	ch := make(chan int)
+	select {
+	case <-ch:
+	default:
+	}
+}
+
+// END f

src/cmd/cover/testdata/html/html.golden

@@ -0,0 +1,10 @@
+// START f
+func f() <span class="cov8" title="1">{
+	ch := make(chan int)
+	select </span>{
+	case &lt;-ch:<span class="cov0" title="0"></span>
+	default:<span class="cov8" title="1"></span>
+	}
+}
+
+// END f

src/cmd/cover/testdata/html/html_test.go

@@ -0,0 +1,7 @@
+package html
+
+import "testing"
+
+func TestAll(t *testing.T) {
+	f()
+}