compute basename manually when target is missing

fix #71

Author: oliverpool

packer/gotool.go

@@ -8,6 +8,7 @@ import (
 	"log"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -351,7 +352,32 @@ type Pkg struct {
 }
 
 func (p *Pkg) Basename() string {
-	return filepath.Base(p.Target)
+	if p.Target != "" {
+		return filepath.Base(p.Target)
+	}
+	// when GOBIN is set in the GOENV file, the target field is empty
+	// see https://github.com/gokrazy/tools/issues/71
+	base := path.Base(p.ImportPath)
+	if isVersionElement(base) {
+		return path.Base(path.Dir(p.ImportPath))
+	}
+	return base
+}
+
+// isVersionElement reports whether s is a well-formed path version element:
+// v2, v3, v10, etc, but not v0, v05, v1.
+// copied from https://github.com/golang/go/blob/go1.22.5/src/cmd/go/internal/load/pkg.go#L1338
+// governed by a BSD-style license
+func isVersionElement(s string) bool {
+	if len(s) < 2 || s[0] != 'v' || s[1] == '0' || s[1] == '1' && len(s) == 2 {
+		return false
+	}
+	for i := 1; i < len(s); i++ {
+		if s[i] < '0' || '9' < s[i] {
+			return false
+		}
+	}
+	return true
 }
 
 func (be *BuildEnv) mainPackage(pkg string) ([]Pkg, error) {

packer/gotool_test.go

@@ -0,0 +1,31 @@
+package packer
+
+import "testing"
+
+func TestPkgBasename(t *testing.T) {
+	f := func(p Pkg, wantBasename string) {
+		t.Helper()
+		got := p.Basename()
+		if got != wantBasename {
+			t.Errorf("pkg.Basename got %q, want %q", got, wantBasename)
+		}
+	}
+
+	f(Pkg{
+		Target: "target-name",
+	}, "target-name")
+
+	f(Pkg{
+		ImportPath: "example.com/import/path",
+		Target:     "target-name",
+	}, "target-name")
+
+	f(Pkg{
+		ImportPath: "example.com/import/path",
+		Target:     "",
+	}, "path")
+	f(Pkg{
+		ImportPath: "example.com/import/path/v2",
+		Target:     "",
+	}, "path")
+}