gh-139640: Fix swallowing syntax warnings in different modules

Revert GH-131993.

Fix swallowing some syntax warnings in different modules if they accidentally
have the same message and are emitted from the same line.

ast.parse() no longer emits syntax warnings for
return/break/continue in finally (see PEP-765) -- they are only
emitted during compilation.

Author: serhiy-storchaka

Include/cpython/warnings.h

@@ -18,9 +18,3 @@ PyAPI_FUNC(int) PyErr_WarnExplicitFormat(
 
 // DEPRECATED: Use PyErr_WarnEx() instead.
 #define PyErr_Warn(category, msg) PyErr_WarnEx((category), (msg), 1)
-
-int _PyErr_WarnExplicitObjectWithContext(
-    PyObject *category,
-    PyObject *message,
-    PyObject *filename,
-    int lineno);

Include/internal/pycore_compile.h

@@ -49,7 +49,8 @@ extern int _PyAST_Preprocess(
     PyObject *filename,
     int optimize,
     int ff_features,
-    int syntax_check_only);
+    int syntax_check_only,
+    int enable_warnings);
 
 
 typedef struct {

Lib/test/test_compile.py

@@ -1664,22 +1664,21 @@ class WeirdDict(dict):
         self.assertRaises(NameError, ns['foo'])
 
     def test_compile_warnings(self):
-        # See gh-131927
-        # Compile warnings originating from the same file and
-        # line are now only emitted once.
+        # Each invocation of compile() emits compiler warnings, even if they
+        # have the same message and line number.
+        source = textwrap.dedent(r"""
+            # tokenizer
+            1or 0  # line 3
+            # code generator
+            1 is 1  # line 5
+        """)
         with warnings.catch_warnings(record=True) as caught:
             warnings.simplefilter("default")
-            compile('1 is 1', '<stdin>', 'eval')
-            compile('1 is 1', '<stdin>', 'eval')
-
-        self.assertEqual(len(caught), 1)
-
-        with warnings.catch_warnings(record=True) as caught:
-            warnings.simplefilter("always")
-            compile('1 is 1', '<stdin>', 'eval')
-            compile('1 is 1', '<stdin>', 'eval')
+            for i in range(2):
+                # Even if compile() is at the same line.
+                compile(source, '<stdin>', 'exec')
 
-        self.assertEqual(len(caught), 2)
+        self.assertEqual([wm.lineno for wm in caught], [3, 5] * 2)
 
     def test_compile_warning_in_finally(self):
         # Ensure that warnings inside finally blocks are
@@ -1690,16 +1689,46 @@ def test_compile_warning_in_finally(self):
             try:
                 pass
             finally:
-                1 is 1
+                1 is 1  # line 5
+                try:
+                    pass
+                finally: # nested
+                    1 is 1  # line 9
         """)
 
         with warnings.catch_warnings(record=True) as caught:
-            warnings.simplefilter("default")
+            warnings.simplefilter("always")
+            compile(source, '<stdin>', 'exec')
+
+        self.assertEqual(sorted(wm.lineno for wm in caught), [5, 9])
+        for wm in caught:
+            self.assertEqual(wm.category, SyntaxWarning)
+            self.assertIn("\"is\" with 'int' literal", str(wm.message))
+
+        # Other code path is used for "try" with "except*".
+        source = textwrap.dedent("""
+            try:
+                pass
+            except *Exception:
+                pass
+            finally:
+                1 is 1  # line 7
+                try:
+                    pass
+                except *Exception:
+                    pass
+                finally: # nested
+                    1 is 1  # line 13
+        """)
+
+        with warnings.catch_warnings(record=True) as caught:
+            warnings.simplefilter("always")
             compile(source, '<stdin>', 'exec')
 
-        self.assertEqual(len(caught), 1)
-        self.assertEqual(caught[0].category, SyntaxWarning)
-        self.assertIn("\"is\" with 'int' literal", str(caught[0].message))
+        self.assertEqual(sorted(wm.lineno for wm in caught), [7, 13])
+        for wm in caught:
+            self.assertEqual(wm.category, SyntaxWarning)
+            self.assertIn("\"is\" with 'int' literal", str(wm.message))
 
 class TestBooleanExpression(unittest.TestCase):
     class Value:

Lib/test/test_pyrepl/test_interact.py

@@ -293,7 +293,7 @@ def f():
         """)
 
         with warnings.catch_warnings(record=True) as caught:
-            warnings.simplefilter("default")
+            warnings.simplefilter("always")
             console.runsource(code)
 
         count = sum("'return' in a 'finally' block" in str(w.message)

Misc/NEWS.d/next/Core_and_Builtins/2025-10-06-10-03-37.gh-issue-139640.gY5oTb.rst

@@ -0,0 +1,5 @@
+Fix swallowing some syntax warnings in different modules if they
+accidentally have the same message and are emitted from the same line.
+:func:`ast.parse` no longer emits syntax warnings for
+``return``/``break``/``continue`` in ``finally`` (see :pep:`765`) -- they are
+only emitted during compilation.

Python/_warnings.c

@@ -1473,28 +1473,6 @@ PyErr_WarnExplicitObject(PyObject *category, PyObject *message,
     return 0;
 }
 
-/* Like PyErr_WarnExplicitObject, but automatically sets up context */
-int
-_PyErr_WarnExplicitObjectWithContext(PyObject *category, PyObject *message,
-                                     PyObject *filename, int lineno)
-{
-    PyObject *unused_filename, *module, *registry;
-    int unused_lineno;
-    int stack_level = 1;
-
-    if (!setup_context(stack_level, NULL, &unused_filename, &unused_lineno,
-                       &module, &registry)) {
-        return -1;
-    }
-
-    int rc = PyErr_WarnExplicitObject(category, message, filename, lineno,
-                                      module, registry);
-    Py_DECREF(unused_filename);
-    Py_DECREF(registry);
-    Py_DECREF(module);
-    return rc;
-}
-
 int
 PyErr_WarnExplicit(PyObject *category, const char *text,
                    const char *filename_str, int lineno,

Python/ast_preprocess.c

@@ -19,6 +19,7 @@ typedef struct {
     int optimize;
     int ff_features;
     int syntax_check_only;
+    int enable_warnings;
 
     _Py_c_array_t cf_finally;       /* context for PEP 765 check */
     int cf_finally_used;
@@ -78,7 +79,7 @@ control_flow_in_finally_warning(const char *kw, stmt_ty n, _PyASTPreprocessState
 static int
 before_return(_PyASTPreprocessState *state, stmt_ty node_)
 {
-    if (state->cf_finally_used > 0) {
+    if (state->enable_warnings && state->cf_finally_used > 0) {
         ControlFlowInFinallyContext *ctx = get_cf_finally_top(state);
         if (ctx->in_finally && ! ctx->in_funcdef) {
             if (!control_flow_in_finally_warning("return", node_, state)) {
@@ -92,7 +93,7 @@ before_return(_PyASTPreprocessState *state, stmt_ty node_)
 static int
 before_loop_exit(_PyASTPreprocessState *state, stmt_ty node_, const char *kw)
 {
-    if (state->cf_finally_used > 0) {
+    if (state->enable_warnings && state->cf_finally_used > 0) {
         ControlFlowInFinallyContext *ctx = get_cf_finally_top(state);
         if (ctx->in_finally && ! ctx->in_loop) {
             if (!control_flow_in_finally_warning(kw, node_, state)) {
@@ -968,14 +969,15 @@ astfold_type_param(type_param_ty node_, PyArena *ctx_, _PyASTPreprocessState *st
 
 int
 _PyAST_Preprocess(mod_ty mod, PyArena *arena, PyObject *filename, int optimize,
-                  int ff_features, int syntax_check_only)
+                  int ff_features, int syntax_check_only, int enable_warnings)
 {
     _PyASTPreprocessState state;
     memset(&state, 0, sizeof(_PyASTPreprocessState));
     state.filename = filename;
     state.optimize = optimize;
     state.ff_features = ff_features;
     state.syntax_check_only = syntax_check_only;
+    state.enable_warnings = enable_warnings;
     if (_Py_CArray_Init(&state.cf_finally, sizeof(ControlFlowInFinallyContext), 20) < 0) {
         return -1;
     }

Python/compile.c

@@ -103,6 +103,7 @@ typedef struct _PyCompiler {
     bool c_save_nested_seqs;     /* if true, construct recursive instruction sequences
                                   * (including instructions for nested code objects)
                                   */
+    int c_disable_warning;
 } compiler;
 
 static int
@@ -135,7 +136,7 @@ compiler_setup(compiler *c, mod_ty mod, PyObject *filename,
     c->c_optimize = (optimize == -1) ? _Py_GetConfig()->optimization_level : optimize;
     c->c_save_nested_seqs = false;
 
-    if (!_PyAST_Preprocess(mod, arena, filename, c->c_optimize, merged, 0)) {
+    if (!_PyAST_Preprocess(mod, arena, filename, c->c_optimize, merged, 0, 1)) {
         return ERROR;
     }
     c->c_st = _PySymtable_Build(mod, filename, &c->c_future);
@@ -765,6 +766,9 @@ _PyCompile_PushFBlock(compiler *c, location loc,
     f->fb_loc = loc;
     f->fb_exit = exit;
     f->fb_datum = datum;
+    if (t == COMPILE_FBLOCK_FINALLY_END) {
+        c->c_disable_warning++;
+    }
     return SUCCESS;
 }
 
@@ -776,6 +780,9 @@ _PyCompile_PopFBlock(compiler *c, fblocktype t, jump_target_label block_label)
     u->u_nfblocks--;
     assert(u->u_fblock[u->u_nfblocks].fb_type == t);
     assert(SAME_JUMP_TARGET_LABEL(u->u_fblock[u->u_nfblocks].fb_block, block_label));
+    if (t == COMPILE_FBLOCK_FINALLY_END) {
+        c->c_disable_warning--;
+    }
 }
 
 fblockinfo *
@@ -1203,6 +1210,9 @@ _PyCompile_Error(compiler *c, location loc, const char *format, ...)
 int
 _PyCompile_Warn(compiler *c, location loc, const char *format, ...)
 {
+    if (c->c_disable_warning) {
+        return 0;
+    }
     va_list vargs;
     va_start(vargs, format);
     PyObject *msg = PyUnicode_FromFormatV(format, vargs);
@@ -1492,7 +1502,7 @@ _PyCompile_AstPreprocess(mod_ty mod, PyObject *filename, PyCompilerFlags *cf,
     if (optimize == -1) {
         optimize = _Py_GetConfig()->optimization_level;
     }
-    if (!_PyAST_Preprocess(mod, arena, filename, optimize, flags, no_const_folding)) {
+    if (!_PyAST_Preprocess(mod, arena, filename, optimize, flags, no_const_folding, 0)) {
         return -1;
     }
     return 0;

Python/errors.c

@@ -1962,8 +1962,8 @@ int
 _PyErr_EmitSyntaxWarning(PyObject *msg, PyObject *filename, int lineno, int col_offset,
                          int end_lineno, int end_col_offset)
 {
-    if (_PyErr_WarnExplicitObjectWithContext(PyExc_SyntaxWarning, msg,
-                                             filename, lineno) < 0)
+    if (PyErr_WarnExplicitObject(PyExc_SyntaxWarning, msg,
+                                 filename, lineno, NULL, NULL) < 0)
     {
         if (PyErr_ExceptionMatches(PyExc_SyntaxWarning)) {
             /* Replace the SyntaxWarning exception with a SyntaxError