Rediscover Go settings only when Go work needs them

internal/gotool/gotool_test.go

@@ -320,9 +320,6 @@ func TestOwnerReusesSettingsUntilInheritedEnvironmentChanges(t *testing.T) {
 
 	cache := filepath.Join(t.TempDir(), "changed-cache")
 	t.Setenv("GOCACHE", cache)
-	if err := owner.Refresh(context.Background()); err != nil {
-		t.Fatal(err)
-	}
 	third, err := owner.Acquire(context.Background())
 	if err != nil {
 		t.Fatal(err)
@@ -332,6 +329,24 @@ func TestOwnerReusesSettingsUntilInheritedEnvironmentChanges(t *testing.T) {
 	}
 }
 
+func TestOwnerAcceptsGoConfigurationWithoutReadableSnapshot(t *testing.T) {
+	clearGoSettings(t)
+	t.Setenv("GOENV", t.TempDir())
+	directory := t.TempDir()
+	if _, err := New(context.Background(), directory); err != nil {
+		t.Fatalf("underlying Go discovery rejected fixture: %v", err)
+	}
+	owner := NewOwner(directory)
+	first, err := owner.Acquire(context.Background())
+	if err != nil {
+		t.Fatalf("owner added a snapshot prerequisite: %v", err)
+	}
+	second, err := owner.Acquire(context.Background())
+	if err != nil || first == second {
+		t.Fatalf("unavailable snapshot should rediscover on demand: first=%p second=%p error=%v", first, second, err)
+	}
+}
+
 func TestOwnerRefreshesWhenPersistentSettingsChange(t *testing.T) {
 	clearGoSettings(t)
 	firstCache := filepath.Join(t.TempDir(), "first-cache")
@@ -355,9 +370,6 @@ func TestOwnerRefreshesWhenPersistentSettingsChange(t *testing.T) {
 		t.Fatalf("initial GOCACHE = %q, want %q", first.settings["GOCACHE"], firstCache)
 	}
 	writeSettings(secondCache)
-	if err := owner.Refresh(context.Background()); err != nil {
-		t.Fatal(err)
-	}
 	second, err := owner.Acquire(context.Background())
 	if err != nil {
 		t.Fatal(err)

internal/gotool/owner.go

@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"errors"
-	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -13,12 +12,13 @@ import (
 // Owner lazily discovers and reuses one Go tool while its inherited
 // environment and persistent settings file remain unchanged.
 type Owner struct {
-	directory string
-	tool      *Tool
-	env       map[string]string
-	file      string
-	contents  []byte
-	fileFound bool
+	directory         string
+	tool              *Tool
+	env               map[string]string
+	file              string
+	contents          []byte
+	fileFound         bool
+	snapshotAvailable bool
 }
 
 // NewOwner creates an operation-local Go tool owner without running Go.
@@ -29,7 +29,7 @@ func NewOwner(directory string) *Owner {
 // Acquire returns the operation's Go tool, rediscovering settings when their
 // process or persistent inputs have changed.
 func (owner *Owner) Acquire(ctx context.Context) (*Tool, error) {
-	if owner.tool != nil {
+	if owner.tool != nil && owner.snapshotAvailable {
 		changed, err := owner.inputsChanged()
 		if err == nil && !changed {
 			return owner.tool, nil
@@ -41,38 +41,24 @@ func (owner *Owner) Acquire(ctx context.Context) (*Tool, error) {
 	return owner.tool, nil
 }
 
-// Refresh checks the owner's inputs after a consumer callback and rediscovers
-// settings when the callback changed the environment or persistent file.
-func (owner *Owner) Refresh(ctx context.Context) error {
-	if owner.tool == nil {
-		return nil
-	}
-	changed, err := owner.inputsChanged()
-	if err == nil && !changed {
-		return nil
-	}
-	return owner.discover(ctx)
-}
-
 func (owner *Owner) discover(ctx context.Context) error {
 	environment := inheritedEnvironment()
 	tool, err := New(ctx, owner.directory)
 	if err != nil {
 		return err
 	}
-	settingsFile, err := resolveSettingsFile(owner.directory, tool.settingsFile)
-	if err != nil {
-		return err
-	}
-	contents, found, err := readSettingsFile(settingsFile)
-	if err != nil {
-		return fmt.Errorf("read Go settings file %q: %w", settingsFile, err)
+	settingsFile, snapshotErr := resolveSettingsFile(owner.directory, tool.settingsFile)
+	var contents []byte
+	var found bool
+	if snapshotErr == nil {
+		contents, found, snapshotErr = readSettingsFile(settingsFile)
 	}
 	owner.tool = tool
 	owner.env = environment
 	owner.file = settingsFile
 	owner.contents = contents
 	owner.fileFound = found
+	owner.snapshotAvailable = snapshotErr == nil
 	return nil
 }