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Filename : ast_transforms.py
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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 typing import Any, List, Tuple, cast

from . import c_ast


def fix_switch_cases(switch_node: c_ast.Switch) -> c_ast.Switch:
    """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: c_ast.Case | c_ast.Default | None = 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: c_ast.Case | c_ast.Default, stmts_list: List[c_ast.Node]
) -> None:
    """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)):
        nested = case_node.stmts.pop()
        stmts_list.append(nested)
        _extract_nested_case(cast(Any, nested), stmts_list)


def fix_atomic_specifiers(
    decl: c_ast.Decl | c_ast.Typedef,
) -> c_ast.Decl | c_ast.Typedef:
    """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: Any = 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: c_ast.Decl | c_ast.Typedef,
) -> Tuple[c_ast.Decl | c_ast.Typedef, bool]:
    """Performs one 'fix' round of atomic specifiers.
    Returns (modified_decl, found) where found is True iff a fix was made.
    """
    parent: Any = decl
    grandparent: Any = None
    node: Any = 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)
    assert grandparent is not None
    cast(Any, grandparent).type = node.type
    if "_Atomic" not in node.type.quals:
        node.type.quals.append("_Atomic")
    return decl, True