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[3.9] bpo-42123: Run the parser two times and only enable invalid rules on the second run (GH-22111) #23011

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Merged
lysnikolaou merged 1 commit into from
Oct 28, 2020
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[3.9] bpo-42123: Run the parser two times and only enable invalid rules on the second run (GH-22111) #23011

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[3.9] bpo-42123: Run the parser two times and only enable invalid rul… 
…es on the second run (GH-22111)

* Implement running the parser a second time for the errors messages

The first parser run is only responsible for detecting whether
there is a `SyntaxError` or not. If there isn't the AST gets returned.
Otherwise, the parser is run a second time with all the `invalid_*`
rules enabled so that all the customized error messages get produced.

(cherry picked from commit bca7014)
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@lysnikolaou
lysnikolaou committed Oct 27, 2020
commit a9947c5457191f764de182d60c0508a67ad4e143
4 changes: 2 additions & 2 deletions Grammar/python.gram
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Original file line number Diff line number Diff line change
Expand Up @@ -535,7 +535,7 @@ yield_expr[expr_ty]:

arguments[expr_ty] (memo):
| a=args [','] &')' { a }
| incorrect_arguments
| invalid_arguments
args[expr_ty]:
| a=','.(starred_expression | named_expression !'=')+ b=[',' k=kwargs {k}] { _PyPegen_collect_call_seqs(p, a, b, EXTRA) }
| a=kwargs { _Py_Call(_PyPegen_dummy_name(p),
Expand Down Expand Up @@ -620,7 +620,7 @@ t_atom[expr_ty]:


# From here on, there are rules for invalid syntax with specialised error messages
incorrect_arguments:
invalid_arguments:
| args ',' '*' { RAISE_SYNTAX_ERROR("iterable argument unpacking follows keyword argument unpacking") }
| a=expression for_if_clauses ',' [args | expression for_if_clauses] {
RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "Generator expression must be parenthesized") }
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-10-23-02-43-24.bpo-42123.64gJWC.rst
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@@ -0,0 +1,3 @@
Run the parser two times. On the first run, disable all the rules that only
generate better error messages to gain performance. If there's a parse
failure, run the parser a second time with those enabled.
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