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The tracer reads co_code[frame.f_lasti] to decide whether a 'return' event was caused by an exception. f_lasti can be -1 (e.g. a frame that hasn't executed an instruction), and co_code[-1] reads the last byte -- the wrong opcode -- which can misreport a normal return as "Call ended by exception". Extract the check into call_ended_by_exception() and return False when f_lasti < 0.
41 lines
1.4 KiB
Python
41 lines
1.4 KiB
Python
"""Tests for call_ended_by_exception, the 'return'-via-exception detector.
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Regression test for https://github.com/cool-RR/PySnooper/issues/260: a frame's
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f_lasti can be -1, and co_code[-1] would read the wrong opcode and misreport a
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normal return as "Call ended by exception".
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"""
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import opcode
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from unittest.mock import Mock
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from pysnooper.tracer import call_ended_by_exception
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def _frame(co_code, f_lasti):
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frame = Mock()
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frame.f_lasti = f_lasti
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frame.f_code.co_code = co_code
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return frame
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def test_negative_f_lasti_is_not_an_exception():
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# Last byte is a non-return opcode, so reading co_code[-1] (the old bug)
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# would misreport an exception. With f_lasti == -1 it must be a normal
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# return.
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co_code = bytes([0, opcode.opmap["NOP"]])
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assert call_ended_by_exception(_frame(co_code, -1), "return", None) is False
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def test_last_opcode_return_is_normal_return():
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co_code = bytes([opcode.opmap["RETURN_VALUE"], 0])
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assert call_ended_by_exception(_frame(co_code, 0), "return", None) is False
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def test_last_opcode_not_return_is_exception():
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co_code = bytes([opcode.opmap["NOP"], 0])
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assert call_ended_by_exception(_frame(co_code, 0), "return", None) is True
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def test_non_return_event_is_never_exception():
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co_code = bytes([opcode.opmap["NOP"], 0])
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assert call_ended_by_exception(_frame(co_code, 0), "call", None) is False
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