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[3.10] bpo-43897: Reject "_" captures and top-level MatchStar in the AST validator (GH-27432) #27435

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Merged
merged 1 commit into from
Jul 29, 2021
Merged

[3.10] bpo-43897: Reject "_" captures and top-level MatchStar in the AST validator (GH-27432) #27435

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6 changes: 5 additions & 1 deletion Lib/test/test_ast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1596,7 +1596,11 @@ def test_stdlib_validates(self):
),
ast.MatchOr(
[pattern_1, pattern_x, ast.MatchSingleton('xxx')]
)
),
ast.MatchAs(name="_"),
ast.MatchStar(name="x"),
ast.MatchSequence([ast.MatchStar("_")]),
ast.MatchMapping([], [], rest="_"),
]

def test_match_validation_pattern(self):
Expand Down
48 changes: 28 additions & 20 deletions Python/ast.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ static int validate_patterns(struct validator *, asdl_pattern_seq *, int);
static int _validate_nonempty_seq(asdl_seq *, const char *, const char *);
static int validate_stmt(struct validator *, stmt_ty);
static int validate_expr(struct validator *, expr_ty, expr_context_ty);
static int validate_pattern(struct validator *, pattern_ty);
static int validate_pattern(struct validator *, pattern_ty, int);

static int
validate_name(PyObject *name)
Expand Down Expand Up @@ -493,16 +493,24 @@ validate_pattern_match_value(struct validator *state, expr_ty exp)
}

static int
validate_pattern(struct validator *state, pattern_ty p)
validate_capture(PyObject *name)
{
if (_PyUnicode_EqualToASCIIString(name, "_")) {
PyErr_Format(PyExc_ValueError, "can't capture name '_' in patterns");
return 0;
}
return validate_name(name);
}

static int
validate_pattern(struct validator *state, pattern_ty p, int star_ok)
{
int ret = -1;
if (++state->recursion_depth > state->recursion_limit) {
PyErr_SetString(PyExc_RecursionError,
"maximum recursion depth exceeded during compilation");
return 0;
}
// Coming soon: https://bugs.python.org/issue43897 (thanks Batuhan)!
// TODO: Ensure no subnodes use "_" as an ordinary identifier
switch (p->kind) {
case MatchValue_kind:
ret = validate_pattern_match_value(state, p->v.MatchValue.value);
Expand All @@ -525,7 +533,7 @@ validate_pattern(struct validator *state, pattern_ty p)
break;
}

if (p->v.MatchMapping.rest && !validate_name(p->v.MatchMapping.rest)) {
if (p->v.MatchMapping.rest && !validate_capture(p->v.MatchMapping.rest)) {
ret = 0;
break;
}
Expand Down Expand Up @@ -575,16 +583,16 @@ validate_pattern(struct validator *state, pattern_ty p)
else {
PyErr_SetString(PyExc_ValueError,
"MatchClass cls field can only contain Name or Attribute nodes.");
state->recursion_depth--;
return 0;
ret = 0;
break;
}
}

for (Py_ssize_t i = 0; i < asdl_seq_LEN(p->v.MatchClass.kwd_attrs); i++) {
PyObject *identifier = asdl_seq_GET(p->v.MatchClass.kwd_attrs, i);
if (!validate_name(identifier)) {
state->recursion_depth--;
return 0;
ret = 0;
break;
}
}

Expand All @@ -596,10 +604,15 @@ validate_pattern(struct validator *state, pattern_ty p)
ret = validate_patterns(state, p->v.MatchClass.kwd_patterns, /*star_ok=*/0);
break;
case MatchStar_kind:
ret = p->v.MatchStar.name == NULL || validate_name(p->v.MatchStar.name);
if (!star_ok) {
PyErr_SetString(PyExc_ValueError, "can't use MatchStar here");
ret = 0;
break;
}
ret = p->v.MatchStar.name == NULL || validate_capture(p->v.MatchStar.name);
break;
case MatchAs_kind:
if (p->v.MatchAs.name && !validate_name(p->v.MatchAs.name)) {
if (p->v.MatchAs.name && !validate_capture(p->v.MatchAs.name)) {
ret = 0;
break;
}
Expand All @@ -609,10 +622,10 @@ validate_pattern(struct validator *state, pattern_ty p)
else if (p->v.MatchAs.name == NULL) {
PyErr_SetString(PyExc_ValueError,
"MatchAs must specify a target name if a pattern is given");
return 0;
ret = 0;
}
else {
ret = validate_pattern(state, p->v.MatchAs.pattern);
ret = validate_pattern(state, p->v.MatchAs.pattern, /*star_ok=*/0);
}
break;
case MatchOr_kind:
Expand Down Expand Up @@ -759,7 +772,7 @@ validate_stmt(struct validator *state, stmt_ty stmt)
}
for (i = 0; i < asdl_seq_LEN(stmt->v.Match.cases); i++) {
match_case_ty m = asdl_seq_GET(stmt->v.Match.cases, i);
if (!validate_pattern(state, m->pattern)
if (!validate_pattern(state, m->pattern, /*star_ok=*/0)
|| (m->guard && !validate_expr(state, m->guard, Load))
|| !validate_body(state, m->body, "match_case")) {
return 0;
Expand Down Expand Up @@ -894,12 +907,7 @@ validate_patterns(struct validator *state, asdl_pattern_seq *patterns, int star_
Py_ssize_t i;
for (i = 0; i < asdl_seq_LEN(patterns); i++) {
pattern_ty pattern = asdl_seq_GET(patterns, i);
if (pattern->kind == MatchStar_kind && !star_ok) {
PyErr_SetString(PyExc_ValueError,
"Can't use MatchStar within this sequence of patterns");
return 0;
}
if (!validate_pattern(state, pattern)) {
if (!validate_pattern(state, pattern, star_ok)) {
return 0;
}
}
Expand Down