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#------------------------------------------------------------------------------
# pycparser: ast_transforms.py
#
# Some utilities used by the parser to create a friendlier AST.
#
# Eli Bendersky [https://eli.thegreenplace.net/]
# 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 is 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 `switch(cond) {}`, block_items would have been None)
for child in (switch_node.stmt.block_items or []):
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)
def fix_atomic_specifiers(decl):
""" Atomic specifiers like _Atomic(type) are unusually structured,
conferring a qualifier upon the contained type.
This function fixes a decl with atomic specifiers to have a sane AST
structure, by removing spurious Typename->TypeDecl pairs and attaching
the _Atomic qualifier in the right place.
"""
# There can be multiple levels of _Atomic in a decl; fix them until a
# fixed point is reached.
while True:
decl, found = _fix_atomic_specifiers_once(decl)
if not found:
break
# Make sure to add an _Atomic qual on the topmost decl if needed. Also
# restore the declname on the innermost TypeDecl (it gets placed in the
# wrong place during construction).
typ = decl
while not isinstance(typ, c_ast.TypeDecl):
try:
typ = typ.type
except AttributeError:
return decl
if '_Atomic' in typ.quals and '_Atomic' not in decl.quals:
decl.quals.append('_Atomic')
if typ.declname is None:
typ.declname = decl.name
return decl
def _fix_atomic_specifiers_once(decl):
""" Performs one 'fix' round of atomic specifiers.
Returns (modified_decl, found) where found is True iff a fix was made.
"""
parent = decl
grandparent = None
node = decl.type
while node is not None:
if isinstance(node, c_ast.Typename) and '_Atomic' in node.quals:
break
try:
grandparent = parent
parent = node
node = node.type
except AttributeError:
# If we've reached a node without a `type` field, it means we won't
# find what we're looking for at this point; give up the search
# and return the original decl unmodified.
return decl, False
assert isinstance(parent, c_ast.TypeDecl)
grandparent.type = node.type
if '_Atomic' not in node.type.quals:
node.type.quals.append('_Atomic')
return decl, True
|
