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bpo-40599: Improve error messages with expected keywords #20039

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bpo-40599: Improve error messages with expected keywords #20039

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40 changes: 39 additions & 1 deletion Parser/pegen/pegen.c
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Original file line number Diff line number Diff line change
Expand Up @@ -780,6 +780,26 @@ _PyPegen_expect_token(Parser *p, int type)
}
Token *t = p->tokens[p->mark];
if (t->type != type) {
int current = p->mark;
if (current >= p->last_err_line) {
if (current > p->last_err_line) {
Py_DECREF(p->err_tokens);
p->err_tokens = PySet_New(0);
p->last_err_line= current;
}
if (PyBytes_AS_STRING(t->bytes)[0] != '\0') {
for (int i=0; i < p->n_keyword_lists; i++) {
if (p->keywords[i] == NULL) {
continue;
}
for (KeywordToken *k = p->keywords[i]; k->type != -1; k++) {
if (k->type == type) {
PySet_Add(p->err_tokens, PyUnicode_FromString(k->str));
}
}
}
}
}
return NULL;
}
p->mark += 1;
Expand Down Expand Up @@ -979,6 +999,7 @@ void
_PyPegen_Parser_Free(Parser *p)
{
Py_XDECREF(p->normalize);
Py_XDECREF(p->err_tokens);
for (int i = 0; i < p->size; i++) {
PyMem_Free(p->tokens[i]);
}
Expand Down Expand Up @@ -1054,6 +1075,8 @@ _PyPegen_Parser_New(struct tok_state *tok, int start_rule, int flags,
p->parsing_started = 0;
p->normalize = NULL;
p->error_indicator = 0;
p->last_err_line = 0;
p->err_tokens = PySet_New(0);

p->starting_lineno = 0;
p->starting_col_offset = 0;
Expand Down Expand Up @@ -1086,7 +1109,22 @@ _PyPegen_run_parser(Parser *p)
RAISE_INDENTATION_ERROR("unexpected unindent");
}
else {
RAISE_SYNTAX_ERROR("invalid syntax");
if (PySet_Size(p->err_tokens)) {
PyObject* comma = PyUnicode_FromString(", ");
if (comma == NULL) {
return NULL;
}
PyObject* error_names = PyUnicode_Join(comma, p->err_tokens);
Py_DECREF(comma);
if (error_names == NULL) {
return NULL;
}
RAISE_SYNTAX_ERROR("Invalid syntax. Expected one of: %U", error_names);
Py_DECREF(error_names);
}
else {
RAISE_SYNTAX_ERROR("Invalid syntax");
}
}
}
return NULL;
Expand Down
2 changes: 2 additions & 0 deletions Parser/pegen/pegen.h
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Expand Up @@ -72,6 +72,8 @@ typedef struct {
int feature_version;
growable_comment_array type_ignore_comments;
Token *known_err_token;
int last_err_line;
PyObject* err_tokens;
} Parser;

typedef struct {
Expand Down