[release-branch.go1.20] internal/coverage/decodemeta: fix coding error in func literal handling

Fix a coding error in coverage meta-data decoding in the method
decodemeta.CoverageMetaDataDecoder.ReadFunc. The code was not
unconditionally assigning the "function literal" field of the
coverage.FuncDesc object passed in, resulting in bad values depending
on what the state of the field happened to be in the object.

Fixes #57942.

Change-Id: I6dfd7d7f7af6004f05c622f9a7116e9f6018cf4f
Reviewed-on: https://go-review.googlesource.com/c/go/+/462955
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
(cherry picked from commit 620399ef0d1390a8f7e7061a45d5304ed087889a)
Reviewed-on: https://go-review.googlesource.com/c/go/+/463418
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>

3 files changed, 57 insertions, 3 deletions

diff --git a/src/cmd/covdata/dump.go b/src/cmd/covdata/dump.go
index 59fdc80d03..62267170ce 100644
--- a/src/cmd/covdata/dump.go
+++ b/src/cmd/covdata/dump.go
@@ -288,6 +288,7 @@ func (d *dstate) VisitFunc(pkgIdx uint32, fnIdx uint32, fd *coverage.FuncDesc) {
 		}
 		fmt.Printf("\nFunc: %s\n", fd.Funcname)
 		fmt.Printf("Srcfile: %s\n", fd.Srcfile)
+		fmt.Printf("Literal: %v\n", fd.Lit)
 	}
 	for i := 0; i < len(fd.Units); i++ {
 		u := fd.Units[i]
diff --git a/src/internal/coverage/decodemeta/decode.go b/src/internal/coverage/decodemeta/decode.go
index 4e80c07f0c..71f1c567ab 100644
--- a/src/internal/coverage/decodemeta/decode.go
+++ b/src/internal/coverage/decodemeta/decode.go
@@ -123,8 +123,6 @@ func (d *CoverageMetaDataDecoder) ReadFunc(fidx uint32, f *coverage.FuncDesc) er
 			})
 	}
 	lit := d.r.ReadULEB128()
-	if lit != 0 {
-		f.Lit = true
-	}
+	f.Lit = lit != 0
 	return nil
 }
diff --git a/src/internal/coverage/test/roundtrip_test.go b/src/internal/coverage/test/roundtrip_test.go
index b26993ffd5..614f56e632 100644
--- a/src/internal/coverage/test/roundtrip_test.go
+++ b/src/internal/coverage/test/roundtrip_test.go
@@ -274,3 +274,58 @@ func TestMetaDataWriterReader(t *testing.T) {
 		inf.Close()
 	}
 }
+
+func TestMetaDataDecodeLitFlagIssue57942(t *testing.T) {
+
+	// Encode a package with a few functions. The funcs alternate
+	// between regular functions and function literals.
+	pp := "foo/bar/pkg"
+	pn := "pkg"
+	mp := "barmod"
+	b, err := encodemeta.NewCoverageMetaDataBuilder(pp, pn, mp)
+	if err != nil {
+		t.Fatalf("making builder: %v", err)
+	}
+	const NF = 6
+	const NCU = 1
+	ln := uint32(10)
+	wantfds := []coverage.FuncDesc{}
+	for fi := uint32(0); fi < NF; fi++ {
+		fis := fmt.Sprintf("%d", fi)
+		fd := coverage.FuncDesc{
+			Funcname: "func" + fis,
+			Srcfile:  "foo" + fis + ".go",
+			Units: []coverage.CoverableUnit{
+				coverage.CoverableUnit{StLine: ln + 1, StCol: 2, EnLine: ln + 3, EnCol: 4, NxStmts: fi + 2},
+			},
+			Lit: (fi % 2) == 0,
+		}
+		wantfds = append(wantfds, fd)
+		b.AddFunc(fd)
+	}
+
+	// Emit into a writer.
+	drws := &slicewriter.WriteSeeker{}
+	b.Emit(drws)
+
+	// Decode the result.
+	drws.Seek(0, io.SeekStart)
+	dec, err := decodemeta.NewCoverageMetaDataDecoder(drws.BytesWritten(), false)
+	if err != nil {
+		t.Fatalf("making decoder: %v", err)
+	}
+	nf := dec.NumFuncs()
+	if nf != NF {
+		t.Fatalf("decoder number of functions: got %d want %d", nf, NF)
+	}
+	var fn coverage.FuncDesc
+	for i := uint32(0); i < uint32(NF); i++ {
+		if err := dec.ReadFunc(i, &fn); err != nil {
+			t.Fatalf("err reading function %d: %v", i, err)
+		}
+		res := cmpFuncDesc(wantfds[i], fn)
+		if res != "" {
+			t.Errorf("ReadFunc(%d): %s", i, res)
+		}
+	}
+}