feat: introduce ErrTooManySteps

Author: jcmfernandes

starlark/eval_test.go

@@ -1158,6 +1158,9 @@ func TestExecutionSteps(t *testing.T) {
 	if !errors.As(err, &canceledErr) {
 		t.Errorf("execution didn't return error starlark.CanceledError")
 	}
+	if !errors.Is(err, starlark.ErrTooManySteps) {
+		t.Errorf("execution didn't return error starlark.ErrTooManySteps")
+	}
 
 	thread.Steps = 0
 	thread.Uncancel()

starlark/interp.go

@@ -6,13 +6,16 @@ import (
 	"fmt"
 	"os"
 
+	"errors"
 	"go.starlark.net/internal/compile"
 	"go.starlark.net/internal/spell"
 	"go.starlark.net/syntax"
 )
 
 const vmdebug = false // TODO(adonovan): use a bitfield of specific kinds of error.
 
+var ErrTooManySteps = errors.New("too many steps")
+
 // TODO(adonovan):
 // - optimize position table.
 // - opt: record MaxIterStack during compilation and preallocate the stack.
@@ -100,7 +103,7 @@ loop:
 			if thread.OnMaxSteps != nil {
 				thread.OnMaxSteps(thread)
 			} else {
-				thread.Cancel("too many steps")
+				thread.CancelWithError(ErrTooManySteps)
 			}
 		}
 		if reasonErr := thread.cancelReason.Load(); reasonErr != nil {