pythongh-106396: Special-case empty format spec to gen empty JoinedSt…

…r node
lysnikolaou · Jul 4, 2023 · a6152ae · a6152ae
1 parent 6c60684
commit a6152ae
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diff --git a/Lib/test/test_fstring.py b/Lib/test/test_fstring.py
@@ -496,6 +496,24 @@ def test_ast_line_numbers_with_parentheses(self):
         self.assertEqual(wat2.end_col_offset, 17)
         self.assertEqual(fstring.end_col_offset, 18)
 
+    def test_ast_fstring_empty_format_spec(self):
+        expr = "f'{expr:}'"
+
+        mod = ast.parse(expr)
+        self.assertEqual(type(mod), ast.Module)
+        self.assertEqual(len(mod.body), 1)
+
+        fstring = mod.body[0].value
+        self.assertEqual(type(fstring), ast.JoinedStr)
+        self.assertEqual(len(fstring.values), 1)
+
+        fv = fstring.values[0]
+        self.assertEqual(type(fv), ast.FormattedValue)
+
+        format_spec = fv.format_spec
+        self.assertEqual(type(format_spec), ast.JoinedStr)
+        self.assertEqual(len(format_spec.values), 0)
+
     def test_docstring(self):
         def f():
             f'''Not a docstring'''

diff --git a/Parser/action_helpers.c b/Parser/action_helpers.c
@@ -997,6 +997,16 @@ _PyPegen_setup_full_format_spec(Parser *p, Token *colon, asdl_expr_seq *spec, in
     if (!spec) {
         return NULL;
     }
+
+    if (asdl_seq_LEN(spec) == 1) {
+        expr_ty e = asdl_seq_GET(spec, 0);
+        if (e->kind == Constant_kind
+                && PyUnicode_Check(e->v.Constant.value)
+                && PyUnicode_GetLength(e->v.Constant.value) == 0) {
+            spec = _Py_asdl_expr_seq_new(0, arena);
+        }
+    }
+
     expr_ty res = _PyAST_JoinedStr(spec, lineno, col_offset, end_lineno, end_col_offset, p->arena);
     if (!res) {
         return NULL;