interp: clarify that Runner.err is for fatal errors only at this point

And simplify the Runner.Run logic so that we don't shove NewExitStatus
errors there right before returning, which is unnecessary confusion.

Author: mvdan

interp/api.go

@@ -131,7 +131,7 @@ type Runner struct {
 
 	noErrExit bool
 
-	err       error // current shell exit code or fatal error
+	fatalErr  error // current fatal error, e.g. from a handler
 	returning bool  // whether the current function `return`ed
 	exiting   bool  // whether the current shell `exit`ed
 
@@ -828,7 +828,7 @@ func (r *Runner) Run(ctx context.Context, node syntax.Node) error {
 		r.Reset()
 	}
 	r.fillExpandConfig(ctx)
-	r.err = nil
+	r.fatalErr = nil
 	r.returning = false
 	r.exiting = false
 	r.filename = ""
@@ -846,13 +846,14 @@ func (r *Runner) Run(ctx context.Context, node syntax.Node) error {
 	default:
 		return fmt.Errorf("node can only be File, Stmt, or Command: %T", node)
 	}
-	if r.exit != 0 {
-		r.setErr(NewExitStatus(uint8(r.exit)))
+	maps.Insert(r.Vars, r.writeEnv.Each)
+	if r.fatalErr != nil {
+		return r.fatalErr
 	}
-	if r.Vars != nil {
-		maps.Insert(r.Vars, r.writeEnv.Each)
+	if r.exit != 0 {
+		return NewExitStatus(uint8(r.exit))
 	}
-	return r.err
+	return nil
 }
 
 // Exited reports whether the last Run call should exit an entire shell. This

interp/builtin.go

@@ -210,7 +210,7 @@ func (r *Runner) builtinCode(ctx context.Context, pos syntax.Pos, name string, a
 			var err error
 			pwd, err = filepath.EvalSymlinks(pwd)
 			if err != nil {
-				r.setErr(err)
+				r.setFatalErr(err) // perhaps overly dramatic?
 				return 1
 			}
 		}

interp/runner.go

@@ -65,7 +65,7 @@ func (r *Runner) fillExpandConfig(ctx context.Context) {
 			r2.stdout = w
 			r2.stmts(ctx, cs.Stmts)
 			r.lastExpandExit = r2.exit
-			return r2.err
+			return r2.fatalErr
 		},
 		ProcSubst: func(ps *syntax.ProcSubst) (string, error) {
 			if runtime.GOOS == "windows" {
@@ -261,9 +261,9 @@ func (r *Runner) handlerCtx(ctx context.Context) context.Context {
 	return context.WithValue(ctx, handlerCtxKey{}, hc)
 }
 
-func (r *Runner) setErr(err error) {
-	if r.err == nil {
-		r.err = err
+func (r *Runner) setFatalErr(err error) {
+	if r.fatalErr == nil {
+		r.fatalErr = err
 	}
 }
 
@@ -280,11 +280,11 @@ func (r *Runner) errf(format string, a ...any) {
 }
 
 func (r *Runner) stop(ctx context.Context) bool {
-	if r.err != nil || r.returning || r.exiting {
+	if r.fatalErr != nil || r.returning || r.exiting {
 		return true
 	}
 	if err := ctx.Err(); err != nil {
-		r.err = err
+		r.fatalErr = err
 		return true
 	}
 	if r.opts[optNoExec] {
@@ -367,7 +367,7 @@ func (r *Runner) cmd(ctx context.Context, cm syntax.Command) {
 		r2 := r.subshell(false)
 		r2.stmts(ctx, cm.Stmts)
 		r.exit = r2.exit
-		r.setErr(r2.err)
+		r.setFatalErr(r2.fatalErr)
 	case *syntax.CallExpr:
 		// Use a new slice, to not modify the slice in the alias map.
 		var args []*syntax.Word
@@ -464,7 +464,7 @@ func (r *Runner) cmd(ctx context.Context, cm syntax.Command) {
 		case syntax.Pipe, syntax.PipeAll:
 			pr, pw, err := os.Pipe()
 			if err != nil {
-				r.setErr(err)
+				r.setFatalErr(err) // not being able to create a pipe is rare but critical
 				return
 			}
 			r2 := r.subshell(false)
@@ -489,7 +489,7 @@ func (r *Runner) cmd(ctx context.Context, cm syntax.Command) {
 				r.exit = r2.exit
 				r.exiting = r2.exiting
 			}
-			r.setErr(r2.err)
+			r.setFatalErr(r2.fatalErr)
 		}
 	case *syntax.IfClause:
 		oldNoErrExit := r.noErrExit
@@ -994,7 +994,7 @@ func (r *Runner) call(ctx context.Context, pos syntax.Pos, args []string) {
 		args, err = r.callHandler(r.handlerCtx(ctx), args)
 		if err != nil {
 			// handler's custom fatal error
-			r.setErr(err)
+			r.setFatalErr(err)
 			return
 		}
 	}
@@ -1034,7 +1034,7 @@ func (r *Runner) exec(ctx context.Context, args []string) {
 			r.exit = int(status)
 		} else {
 			// handler's custom fatal error
-			r.setErr(err)
+			r.setFatalErr(err)
 			r.exit = 1
 		}
 	} else {
@@ -1066,7 +1066,7 @@ func (r *Runner) open(ctx context.Context, path string, flags int, mode os.FileM
 			r.errf("%v\n", err)
 		}
 	default: // handler's custom fatal error
-		r.setErr(err)
+		r.setFatalErr(err)
 	}
 	return nil, err
 }