cmd/cover: take default value of total only once.

Defaulting total to 1 for each function, adds up to the
counting error. testing/cover.go already does this once.

Fixes #20515

Change-Id: I0e3f524c2ccb628eb9a8f0a1f81c22365c24cf9a
Reviewed-on: https://go-review.googlesource.com/44337
Run-TryBot: Dhananjay Nakrani <dhananjayn@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

4 files changed, 65 insertions, 9 deletions

diff --git a/src/cmd/cover/cover_test.go b/src/cmd/cover/cover_test.go
index 81ac8ae467..1584a73b59 100644
--- a/src/cmd/cover/cover_test.go
+++ b/src/cmd/cover/cover_test.go
@@ -26,10 +26,11 @@ const (
 
 var (
 	// Files we use.
-	testMain    = filepath.Join(testdata, "main.go")
-	testTest    = filepath.Join(testdata, "test.go")
-	coverInput  = filepath.Join(testdata, "test_line.go")
-	coverOutput = filepath.Join(testdata, "test_cover.go")
+	testMain     = filepath.Join(testdata, "main.go")
+	testTest     = filepath.Join(testdata, "test.go")
+	coverInput   = filepath.Join(testdata, "test_line.go")
+	coverOutput  = filepath.Join(testdata, "test_cover.go")
+	coverProfile = filepath.Join(testdata, "profile.cov")
 )
 
 var debug = false // Keeps the rewritten files around if set.
@@ -102,6 +103,25 @@ func TestCover(t *testing.T) {
 	}
 }
 
+// Makes sure that `cover -func=profile.cov` reports accurate coverage.
+// Issue #20515.
+func TestCoverFunc(t *testing.T) {
+	// go tool cover -func ./testdata/profile.cov
+	cmd := exec.Command(testenv.GoToolPath(t), "tool", "cover", "-func", coverProfile)
+	out, err := cmd.Output()
+	if err != nil {
+		if ee, ok := err.(*exec.ExitError); ok {
+			t.Logf("%s", ee.Stderr)
+		}
+		t.Fatal(err)
+	}
+
+	if got, err := regexp.Match(".*total:.*100.0.*", out); err != nil || !got {
+		t.Logf("%s", out)
+		t.Errorf("invalid coverage counts. got=(%v, %v); want=(true; nil)", got, err)
+	}
+}
+
 func run(c *exec.Cmd, t *testing.T) {
 	c.Stdout = os.Stdout
 	c.Stderr = os.Stderr
diff --git a/src/cmd/cover/func.go b/src/cmd/cover/func.go
index 66ec242a40..05c7c12c99 100644
--- a/src/cmd/cover/func.go
+++ b/src/cmd/cover/func.go
@@ -66,12 +66,12 @@ func funcOutput(profile, outputFile string) error {
 		// Now match up functions and profile blocks.
 		for _, f := range funcs {
 			c, t := f.coverage(profile)
-			fmt.Fprintf(tabber, "%s:%d:\t%s\t%.1f%%\n", fn, f.startLine, f.name, 100.0*float64(c)/float64(t))
+			fmt.Fprintf(tabber, "%s:%d:\t%s\t%.1f%%\n", fn, f.startLine, f.name, percent(c, t))
 			total += t
 			covered += c
 		}
 	}
-	fmt.Fprintf(tabber, "total:\t(statements)\t%.1f%%\n", 100.0*float64(covered)/float64(total))
+	fmt.Fprintf(tabber, "total:\t(statements)\t%.1f%%\n", percent(covered, total))
 
 	return nil
 }
@@ -147,9 +147,6 @@ func (f *FuncExtent) coverage(profile *Profile) (num, den int64) {
 			covered += int64(b.NumStmt)
 		}
 	}
-	if total == 0 {
-		total = 1 // Avoid zero denominator.
-	}
 	return covered, total
 }
 
@@ -162,3 +159,10 @@ func findFile(file string) (string, error) {
 	}
 	return filepath.Join(pkg.Dir, file), nil
 }
+
+func percent(covered, total int64) float64 {
+	if total == 0 {
+		total = 1 // Avoid zero denominator.
+	}
+	return 100.0 * float64(covered) / float64(total)
+}
diff --git a/src/cmd/cover/testdata/p.go b/src/cmd/cover/testdata/p.go
new file mode 100644
index 0000000000..ce3a8c0612
--- /dev/null
+++ b/src/cmd/cover/testdata/p.go
@@ -0,0 +1,27 @@
+// Copyright 2017 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.
+
+// A package such that there are 3 functions with zero total and covered lines.
+// And one with 1 total and covered lines. Reproduces issue #20515.
+package p
+
+//go:noinline
+func A() {
+
+}
+
+//go:noinline
+func B() {
+
+}
+
+//go:noinline
+func C() {
+
+}
+
+//go:noinline
+func D() int64 {
+	return 42
+}
diff --git a/src/cmd/cover/testdata/profile.cov b/src/cmd/cover/testdata/profile.cov
new file mode 100644
index 0000000000..db08602d5a
--- /dev/null
+++ b/src/cmd/cover/testdata/profile.cov
@@ -0,0 +1,5 @@
+mode: set
+./testdata/p.go:10.10,12.2 0 0
+./testdata/p.go:15.10,17.2 0 0
+./testdata/p.go:20.10,22.2 0 0
+./testdata/p.go:25.16,27.2 1 1