more errors

dataconv/share.go

@@ -249,6 +249,7 @@ var (
 	}
 )
 
+// shardDictLen returns the length of the underlying dictionary.
 func shardDictLen(_ *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	if err := starlark.UnpackPositionalArgs(b.Name(), args, kwargs, 0); err != nil {
 		return nil, err
@@ -257,6 +258,8 @@ func shardDictLen(_ *starlark.Thread, b *starlark.Builtin, args starlark.Tuple,
 	return starlark.MakeInt(l), nil
 }
 
+// shardDictPerform calls the given function with the underlying receiver dictionary, and returns the result.
+// The function must be callable, like def perform(fn).
 func shardDictPerform(thread *starlark.Thread, b *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
 	// get the perform function
 	var pr starlark.Value

dataconv/share_test.go

@@ -212,6 +212,28 @@ func TestSharedDict_Functions(t *testing.T) {
 			`),
 			wantErr: `len: got 1 arguments, want 0`,
 		},
+		{
+			name: `attr: custom perform`,
+			script: itn.HereDoc(`
+				load('share', 'sd')
+				def act(d):
+					d["cnt"] = d.get("cnt", 100) + 1
+				assert.eq(sd.get("cnt"), None)
+				sd.perform(act)
+				assert.eq(sd["cnt"], 101)
+			`),
+		},
+		{
+			name: `attr: custom perform -- error`,
+			script: itn.HereDoc(`
+				load('share', 'sd')
+				def ungood(d):
+					fail("not good~{}".format(d))
+				sd["foo"] = "bar"
+				sd.perform(ungood)
+			`),
+			wantErr: `fail: not good~{"foo": "bar"}`,
+		},
 		{
 			name: `attr: custom perform`,
 			script: itn.HereDoc(`