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EDIT :: ast_transforms.py

#------------------------------------------------------------------------------ # 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

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