Assertion failure when part of expression is unreachable #761
Description
This code results in an assertion failure within mypyc:
import sys
y = sys.platform == "x" and sys.version_info < (3, 6)Here's the traceback:
Traceback (most recent call last):
File "build/setup.py", line 5, in <module>
ext_modules=mypycify(['t.py'], opt_level="3"),
File "/home/jukka/src/mypy/mypyc/build.py", line 492, in mypycify
skip_cgen_input=skip_cgen_input,
File "/home/jukka/src/mypy/mypyc/build.py", line 401, in mypyc_build
compiler_options=compiler_options)
File "/home/jukka/src/mypy/mypyc/build.py", line 201, in generate_c
result, compiler_options=compiler_options, errors=errors, groups=groups)
File "/home/jukka/src/mypy/mypyc/codegen/emitmodule.py", line 408, in compile_modules_to_c
modules = compile_modules_to_ir(result, mapper, compiler_options, errors)
File "/home/jukka/src/mypy/mypyc/codegen/emitmodule.py", line 255, in compile_modules_to_ir
scc_ir = compile_scc_to_ir(trees, result, mapper, compiler_options, errors)
File "/home/jukka/src/mypy/mypyc/codegen/emitmodule.py", line 207, in compile_scc_to_ir
scc, result.graph, result.types, mapper, compiler_options, errors
File "/usr/local/lib/python3.6/contextlib.py", line 52, in inner
return func(*args, **kwds)
File "/home/jukka/src/mypy/mypyc/irbuild/main.py", line 80, in build_ir
transform_mypy_file(builder, module)
File "/home/jukka/src/mypy/mypyc/irbuild/main.py", line 123, in transform_mypy_file
builder.accept(node)
File "/home/jukka/src/mypy/mypyc/irbuild/builder.py", line 160, in accept
node.accept(self.visitor)
File "/home/jukka/src/mypy/mypy/nodes.py", line 1063, in accept
return visitor.visit_assignment_stmt(self)
File "/home/jukka/src/mypy/mypyc/irbuild/visitor.py", line 135, in visit_assignment_stmt
transform_assignment_stmt(self.builder, stmt)
File "/home/jukka/src/mypy/mypyc/irbuild/statement.py", line 83, in transform_assignment_stmt
rvalue_reg = builder.accept(stmt.rvalue)
File "/home/jukka/src/mypy/mypyc/irbuild/builder.py", line 149, in accept
res = node.accept(self.visitor)
File "/home/jukka/src/mypy/mypy/nodes.py", line 1737, in accept
return visitor.visit_op_expr(self)
File "/home/jukka/src/mypy/mypyc/irbuild/visitor.py", line 199, in visit_op_expr
return transform_op_expr(self.builder, expr)
File "/home/jukka/src/mypy/mypyc/irbuild/expression.py", line 322, in transform_op_expr
return builder.shortcircuit_expr(expr)
File "/home/jukka/src/mypy/mypyc/irbuild/builder.py", line 795, in shortcircuit_expr
expr.line
File "/home/jukka/src/mypy/mypyc/irbuild/ll_builder.py", line 821, in shortcircuit_helper
right_value = right()
File "/home/jukka/src/mypy/mypyc/irbuild/builder.py", line 794, in <lambda>
lambda: self.accept(expr.right),
File "/home/jukka/src/mypy/mypyc/irbuild/builder.py", line 149, in accept
res = node.accept(self.visitor)
File "/home/jukka/src/mypy/mypy/nodes.py", line 1762, in accept
return visitor.visit_comparison_expr(self)
File "/home/jukka/src/mypy/mypyc/irbuild/visitor.py", line 208, in visit_comparison_expr
return transform_comparison_expr(self.builder, expr)
File "/home/jukka/src/mypy/mypyc/irbuild/expression.py", line 479, in transform_comparison_expr
return go(0, builder.accept(e.operands[0]))
File "/home/jukka/src/mypy/mypyc/irbuild/builder.py", line 149, in accept
res = node.accept(self.visitor)
File "/home/jukka/src/mypy/mypy/nodes.py", line 1497, in accept
return visitor.visit_member_expr(self)
File "/home/jukka/src/mypy/mypyc/irbuild/visitor.py", line 187, in visit_member_expr
return transform_member_expr(self.builder, expr)
File "/home/jukka/src/mypy/mypyc/irbuild/expression.py", line 106, in transform_member_expr
obj = builder.accept(expr.expr)
File "/home/jukka/src/mypy/mypyc/irbuild/builder.py", line 149, in accept
res = node.accept(self.visitor)
File "/home/jukka/src/mypy/mypy/nodes.py", line 1477, in accept
return visitor.visit_name_expr(self)
File "/home/jukka/src/mypy/mypyc/irbuild/visitor.py", line 184, in visit_name_expr
return transform_name_expr(self.builder, expr)
File "/home/jukka/src/mypy/mypyc/irbuild/expression.py", line 44, in transform_name_expr
assert expr.node, "RefExpr not resolved"
t.py:3: AssertionError: RefExpr not resolved
I haven't looked into this in detail yet, but I believe that the problem is that sys.version_info < (3, 6) is not semantically analyzed, since it's considered unreachable, but we assume that everything has been semantically analyzed. Instead, we could generate code that raises an exception if we reach code that is supposed to be unreachable.
As a workaround, we can rewrite the platform check in a way that isn't recognized by mypy, such as by using the in operator:
import sys
y = sys.platform in ["x"] and sys.version_info < (3, 6)