Viewing file:  ast_transforms.py (3.48 KB) -rw-r--r--
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#------------------------------------------------------------------------------
# pycparser: ast_transforms.py
#
# Some utilities used by the parser to create a friendlier AST.
#
# Copyright (C) 2008-2015, Eli Bendersky
# License: BSD
#------------------------------------------------------------------------------
from . import c_ast
def fix_switch_cases(switch_node):
""" The 'case' statements in a 'switch' come out of parsing with one
child node, so subsequent statements are just tucked to the parent
Compound. Additionally, consecutive (fall-through) case statements
come out messy. This is a peculiarity of the C grammar. The following:
switch (myvar) {
case 10:
k = 10;
p = k + 1;
return 10;
case 20:
case 30:
return 20;
default:
break;
}
Creates this tree (pseudo-dump):
Switch
ID: myvar
Compound:
Case 10:
k = 10
p = k + 1
return 10
Case 20:
Case 30:
return 20
Default:
break
The goal of this transform it to fix this mess, turning it into the
following:
Switch
ID: myvar
Compound:
Case 10:
k = 10
p = k + 1
return 10
Case 20:
Case 30:
return 20
Default:
break
A fixed AST node is returned. The argument may be modified.
"""
assert isinstance(switch_node, c_ast.Switch)
if not isinstance(switch_node.stmt, c_ast.Compound):
return switch_node
# The new Compound child for the Switch, which will collect children in the
# correct order
new_compound = c_ast.Compound([], switch_node.stmt.coord)
# The last Case/Default node
last_case = None
# Goes over the children of the Compound below the Switch, adding them
# either directly below new_compound or below the last Case as appropriate
for child in switch_node.stmt.block_items:
if isinstance(child, (c_ast.Case, c_ast.Default)):
# If it's a Case/Default:
# 1. Add it to the Compound and mark as "last case"
# 2. If its immediate child is also a Case or Default, promote it
# to a sibling.
new_compound.block_items.append(child)
_extract_nested_case(child, new_compound.block_items)
last_case = new_compound.block_items[-1]
else:
# Other statements are added as children to the last case, if it
# exists.
if last_case is None:
new_compound.block_items.append(child)
else:
last_case.stmts.append(child)
switch_node.stmt = new_compound
return switch_node
def _extract_nested_case(case_node, stmts_list):
""" Recursively extract consecutive Case statements that are made nested
by the parser and add them to the stmts_list.
"""
if isinstance(case_node.stmts[0], (c_ast.Case, c_ast.Default)):
stmts_list.append(case_node.stmts.pop())
_extract_nested_case(stmts_list[-1], stmts_list)
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