[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 <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
(cherry picked from commit 620399e)
Reviewed-on: https://go-review.googlesource.com/c/go/+/463418
Reviewed-by: Than McIntosh <[email protected]>
Run-TryBot: Matthew Dempsky <[email protected]>
Auto-Submit: Matthew Dempsky <[email protected]>

Author: thanm

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]

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
 }

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)
+		}
+	}
+}