Keep publication recovery usable after cold Go tool runs

internal/gotool/recovery.go

@@ -0,0 +1,108 @@
+package gotool
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/mod/modfile"
+
+	"go.maximumdirect.net/releasekit/internal/process"
+)
+
+const releaseKitModule = "go.maximumdirect.net/releasekit"
+const releaseKitCommand = releaseKitModule + "/cmd/releasekit"
+
+// RecoveryTool returns module-selected Go arguments for a later invocation.
+// An empty result means this module does not select ReleaseKit. API-only modules
+// receive private alternate module files that outlive launcher-owned bootstraps.
+func RecoveryTool(ctx context.Context, moduleDir, recordDir string) ([]string, error) {
+	path := filepath.Join(moduleDir, "go.mod")
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	module, err := modfile.Parse(path, data, nil)
+	if err != nil {
+		return nil, err
+	}
+	for _, tool := range module.Tool {
+		if tool.Path == releaseKitCommand {
+			return []string{"-C", moduleDir, "tool", "-modfile=", releaseKitCommand}, nil
+		}
+	}
+	// Ask Go about the selected module graph, including transitive dependencies.
+	// This reads real module metadata, independently of a launcher's -modfile.
+	var selection bytes.Buffer
+	err = process.Run(ctx, process.Invocation{
+		Args: []string{"go", "list", "-e", "-json", "-mod=readonly", "-modfile=", "-m", releaseKitModule},
+		Dir:  moduleDir, Env: map[string]string{"GOWORK": "off", "GOTOOLCHAIN": "local"},
+		Stdout: &selection, Stderr: io.Discard,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("identify recovery tool selection: %w", err)
+	}
+	var selected struct {
+		Main    bool
+		Version string
+		Error   *struct{ Err string }
+	}
+	if err := json.Unmarshal(selection.Bytes(), &selected); err != nil {
+		return nil, err
+	}
+	if !selected.Main && selected.Version == "" {
+		// A source-built CLI also supports consumers without a module dependency.
+		return nil, nil
+	}
+	if selected.Error != nil {
+		return nil, fmt.Errorf("identify recovery tool selection: %s", selected.Error.Err)
+	}
+	if err := module.AddTool(releaseKitCommand); err != nil {
+		return nil, err
+	}
+	data, err = module.Format()
+	if err != nil {
+		return nil, err
+	}
+	sums, err := os.ReadFile(filepath.Join(moduleDir, "go.sum"))
+	if err != nil && !os.IsNotExist(err) {
+		return nil, err
+	}
+	if err := os.MkdirAll(recordDir, 0700); err != nil {
+		return nil, err
+	}
+	directory, err := os.MkdirTemp(recordDir, "recovery-")
+	if err != nil {
+		return nil, fmt.Errorf("create durable recovery module directory: %w", err)
+	}
+	complete := false
+	defer func() {
+		if !complete {
+			_ = os.RemoveAll(directory)
+		}
+	}()
+	alternate := filepath.Join(directory, "releasekit.mod")
+	if err := os.WriteFile(alternate, data, 0600); err != nil {
+		return nil, err
+	}
+	if err := os.WriteFile(filepath.Join(directory, "releasekit.sum"), sums, 0600); err != nil {
+		return nil, err
+	}
+	// go tool accepts an alternate module file but has no -mod flag. Prepare
+	// the private graph and sums before the later read-only tool invocation.
+	captured := &combinedWriter{mode: captureStatus}
+	err = process.Run(ctx, process.Invocation{
+		Args: []string{"go", "list", "-mod=mod", "-modfile=" + alternate, "-deps", releaseKitCommand},
+		Dir:  moduleDir, Env: map[string]string{"GOWORK": "off", "GOTOOLCHAIN": "local"},
+		Stdout: captured, Stderr: captured,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("prepare recovery tool: %w: %s", err, diagnosticText(captured.take(), captured.omitted()))
+	}
+	complete = true
+	return []string{"-C", moduleDir, "tool", "-modfile=" + alternate, releaseKitCommand}, nil
+}