Pass absolute source paths to go tool cover

ChangeLog

@@ -1,3 +1,8 @@
+Version 1.32.1
+--------------
+    * Pass absolute source paths to `go tool cover` so that coverage builds
+      report correct file positions under Go 1.27 (#372)
+
 Version 1.32.0
 --------------
     * Allow passing command-line arguments to go_test targets (#368)

VERSION

@@ -1 +1 @@
-1.32.0
+1.32.1

tools/please_go/cover/BUILD

@@ -2,7 +2,10 @@ subinclude("//build_defs:go")
 
 filegroup(
     name = "srcs",
-    srcs = ["cover.go"],
+    srcs = glob(
+        include = ["*.go"],
+        exclude = ["*_test.go"],
+    ),
     visibility = ["//tools/please_go:bootstrap"],
 )
 
@@ -12,3 +15,13 @@ go_library(
     visibility = ["//tools/please_go/..."],
     deps = ["//tools/please_go/install/toolchain"],
 )
+
+go_test(
+    name = "cover_test",
+    srcs = ["cover_test.go"],
+    deps = [
+        ":cover",
+        "///third_party/go/github.com_stretchr_testify//assert",
+        "///third_party/go/github.com_stretchr_testify//require",
+    ],
+)

tools/please_go/cover/cover.go

@@ -21,6 +21,15 @@ func WriteCoverage(goTool, coverTool, covercfg, output, pkg string, srcs []strin
 	if err != nil {
 		return err
 	}
+	// `go tool cover` copies these into `//line` directives, and since Go 1.27
+	// (go.dev/issue/70478) a relative one resolves against the file's own directory.
+	for i, src := range srcs {
+		abs, err := filepath.Abs(src)
+		if err != nil {
+			return err
+		}
+		srcs[i] = abs
+	}
 	const pkgConfigFile = "pkgcfg"
 	b, _ := json.Marshal(coverConfig{
 		OutConfig:   covercfg,
@@ -34,7 +43,7 @@ func WriteCoverage(goTool, coverTool, covercfg, output, pkg string, srcs []strin
 	var buf bytes.Buffer
 	// 1.21 requires a cover vars file to be written into the output file list
 	if coverTool != "" || needs121CoverVars(goTool) {
-		buf.WriteString(filepath.Join(filepath.Dir(srcs[0]), "_covervars.cover.go\n"))
+		buf.WriteString(filepath.Join(filepath.Dir(srcs[0]), "_covervars.cover.go") + "\n")
 	}
 	for _, src := range srcs {
 		buf.WriteString(strings.TrimSuffix(src, ".go") + ".cover.go\n")

tools/please_go/cover/cover_test.go

@@ -0,0 +1,42 @@
+package cover
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestWriteCoveragePassesAbsoluteSources(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	pkgDir := filepath.Join(tmpDir, "src", "mypkg")
+	require.NoError(t, os.MkdirAll(pkgDir, 0755))
+	require.NoError(t, os.WriteFile(filepath.Join(pkgDir, "mypkg.go"), []byte("package mypkg\n"), 0644))
+
+	// A fake cover tool that records the arguments it was given.
+	argsFile := filepath.Join(tmpDir, "args")
+	coverTool := filepath.Join(tmpDir, "cover.sh")
+	script := "#!/bin/sh\nprintf '%s\\n' \"$@\" > \"" + argsFile + "\"\n"
+	require.NoError(t, os.WriteFile(coverTool, []byte(script), 0755))
+
+	t.Chdir(tmpDir)
+	src := filepath.Join("src", "mypkg", "mypkg.go")
+	outfilelist := filepath.Join(tmpDir, "outfilelist")
+	require.NoError(t, WriteCoverage("go", coverTool, filepath.Join(tmpDir, "covcfg"), outfilelist, "example.com/mypkg", []string{src}))
+
+	args, err := os.ReadFile(argsFile)
+	require.NoError(t, err)
+	assert.Contains(t, strings.Fields(string(args)), filepath.Join(pkgDir, "mypkg.go"))
+	assert.NotContains(t, strings.Fields(string(args)), src)
+
+	list, err := os.ReadFile(outfilelist)
+	require.NoError(t, err)
+	assert.Equal(t, []string{
+		filepath.Join(pkgDir, "_covervars.cover.go"),
+		filepath.Join(pkgDir, "mypkg.cover.go"),
+	}, strings.Split(strings.TrimSpace(string(list)), "\n"))
+}