1 files changed, 98 insertions, 0 deletions
diff --git a/src/cmd/internal/cov/read_test.go b/src/cmd/internal/cov/read_test.go
new file mode 100644
index 0000000000..cef03fa323
--- /dev/null
+++ b/src/cmd/internal/cov/read_test.go
@@ -0,0 +1,98 @@
+// Copyright 2022 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.
+
+package cov_test
+
+import (
+	"cmd/internal/cov"
+	"fmt"
+	"internal/coverage"
+	"internal/coverage/decodecounter"
+	"internal/coverage/decodemeta"
+	"internal/coverage/pods"
+	"internal/testenv"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// visitor implements the CovDataVisitor interface in a very stripped
+// down way, just keeps track of interesting events.
+type visitor struct {
+	metaFileCount    int
+	counterFileCount int
+	funcCounterData  int
+	metaFuncCount    int
+}
+
+func (v *visitor) BeginPod(p pods.Pod) {}
+func (v *visitor) EndPod(p pods.Pod)   {}
+func (v *visitor) VisitMetaDataFile(mdf string, mfr *decodemeta.CoverageMetaFileReader) {
+	v.metaFileCount++
+}
+func (v *visitor) BeginCounterDataFile(cdf string, cdr *decodecounter.CounterDataReader, dirIdx int) {
+	v.counterFileCount++
+}
+func (v *visitor) EndCounterDataFile(cdf string, cdr *decodecounter.CounterDataReader, dirIdx int) {}
+func (v *visitor) VisitFuncCounterData(payload decodecounter.FuncPayload)                          { v.funcCounterData++ }
+func (v *visitor) EndCounters()                                                                    {}
+func (v *visitor) BeginPackage(pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32)              {}
+func (v *visitor) EndPackage(pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32)                {}
+func (v *visitor) VisitFunc(pkgIdx uint32, fnIdx uint32, fd *coverage.FuncDesc)                    { v.metaFuncCount++ }
+func (v *visitor) Finish()                                                                         {}
+
+func TestIssue58411(t *testing.T) {
+	testenv.MustHaveGoBuild(t)
+
+	// Build a tiny test program with -cover. Smallness is important;
+	// it is one of the factors that triggers issue 58411.
+	d := t.TempDir()
+	exepath := filepath.Join(d, "small.exe")
+	path := filepath.Join("testdata", "small.go")
+	cmd := testenv.Command(t, testenv.GoToolPath(t), "build",
+		"-o", exepath, "-cover", path)
+	b, err := cmd.CombinedOutput()
+	if len(b) != 0 {
+		t.Logf("## build output:\n%s", b)
+	}
+	if err != nil {
+		t.Fatalf("build error: %v", err)
+	}
+
+	// Run to produce coverage data. Note the large argument; we need a large
+	// argument (more than 4k) to trigger the bug, but the overall file
+	// has to remain small (since large files will be read with mmap).
+	covdir := filepath.Join(d, "covdata")
+	if err = os.Mkdir(covdir, 0777); err != nil {
+		t.Fatalf("creating covdir: %v", err)
+	}
+	large := fmt.Sprintf("%07999d", 0)
+	cmd = testenv.Command(t, exepath, "1", "2", "3", large)
+	cmd.Dir = covdir
+	cmd.Env = append(os.Environ(), "GOCOVERDIR="+covdir)
+	b, err = cmd.CombinedOutput()
+	if err != nil {
+		t.Logf("## run output:\n%s", b)
+		t.Fatalf("build error: %v", err)
+	}
+
+	vis := &visitor{}
+
+	// Read resulting coverage data. Without the fix, this would
+	// yield a "short read" error.
+	const verbosityLevel = 0
+	const flags = 0
+	cdr := cov.MakeCovDataReader(vis, []string{covdir}, verbosityLevel, flags, nil)
+	err = cdr.Visit()
+	if err != nil {
+		t.Fatalf("visit failed: %v", err)
+	}
+
+	// make sure we saw a few things just for grins
+	const want = "{metaFileCount:1 counterFileCount:1 funcCounterData:1 metaFuncCount:1}"
+	got := fmt.Sprintf("%+v", *vis)
+	if want != got {
+		t.Errorf("visitor contents: want %v got %v\n", want, got)
+	}
+}