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bpo-39934: Account for control blocks in 'except' in compiler. #22395

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Sep 25, 2020
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bpo-39934: Account for control blocks in 'except' in compiler. #22395

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300314b
Account for control blocks in 'except' in compiler. Fixes #39934.
markshannon Sep 24, 2020
945e68f
Change nesting test from doctest to unittest.
markshannon Sep 25, 2020
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53 changes: 53 additions & 0 deletions Lib/test/test_syntax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -777,6 +777,59 @@
>>> import ä £
Traceback (most recent call last):
SyntaxError: invalid character '£' (U+00A3)

Too many implicit blocks in named exception handlers

>>> try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... try:
... raise Exception
... except Exception as e:
... pass
...
Traceback (most recent call last):
SyntaxError: too many statically nested blocks

"""

import re
Expand Down
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-09-24-12-15-45.bpo-39934.YVHTCF.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Correctly count control blocks in 'except' in compiler. Ensures that a
syntax error, rather a fatal error, occurs for deeply nested, named
exception handlers.
15 changes: 10 additions & 5 deletions Python/compile.c
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Original file line number Diff line number Diff line change
Expand Up @@ -108,8 +108,8 @@ It's called a frame block to distinguish it from a basic block in the
compiler IR.
*/

enum fblocktype { WHILE_LOOP, FOR_LOOP, EXCEPT, FINALLY_TRY, FINALLY_END,
WITH, ASYNC_WITH, HANDLER_CLEANUP, POP_VALUE };
enum fblocktype { WHILE_LOOP, FOR_LOOP, TRY_EXCEPT, FINALLY_TRY, FINALLY_END,
WITH, ASYNC_WITH, HANDLER_CLEANUP, POP_VALUE, EXCEPTION_HANDLER };

struct fblockinfo {
enum fblocktype fb_type;
Expand Down Expand Up @@ -1665,6 +1665,7 @@ compiler_unwind_fblock(struct compiler *c, struct fblockinfo *info,
{
switch (info->fb_type) {
case WHILE_LOOP:
case EXCEPTION_HANDLER:
return 1;

case FOR_LOOP:
Expand All @@ -1675,7 +1676,7 @@ compiler_unwind_fblock(struct compiler *c, struct fblockinfo *info,
ADDOP(c, POP_TOP);
return 1;

case EXCEPT:
case TRY_EXCEPT:
ADDOP(c, POP_BLOCK);
return 1;

Expand Down Expand Up @@ -3060,14 +3061,17 @@ compiler_try_except(struct compiler *c, stmt_ty s)
return 0;
ADDOP_JUMP(c, SETUP_FINALLY, except);
compiler_use_next_block(c, body);
if (!compiler_push_fblock(c, EXCEPT, body, NULL, NULL))
if (!compiler_push_fblock(c, TRY_EXCEPT, body, NULL, NULL))
return 0;
VISIT_SEQ(c, stmt, s->v.Try.body);
ADDOP(c, POP_BLOCK);
compiler_pop_fblock(c, EXCEPT, body);
compiler_pop_fblock(c, TRY_EXCEPT, body);
ADDOP_JUMP(c, JUMP_FORWARD, orelse);
n = asdl_seq_LEN(s->v.Try.handlers);
compiler_use_next_block(c, except);
/* Runtime will push a block here, so we need to account for that */
if (!compiler_push_fblock(c, EXCEPTION_HANDLER, NULL, NULL, NULL))
return 0;
for (i = 0; i < n; i++) {
excepthandler_ty handler = (excepthandler_ty)asdl_seq_GET(
s->v.Try.handlers, i);
Expand Down Expand Up @@ -3152,6 +3156,7 @@ compiler_try_except(struct compiler *c, stmt_ty s)
}
compiler_use_next_block(c, except);
}
compiler_pop_fblock(c, EXCEPTION_HANDLER, NULL);
ADDOP(c, RERAISE);
compiler_use_next_block(c, orelse);
VISIT_SEQ(c, stmt, s->v.Try.orelse);
Expand Down