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