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--enable-error-code code does not enable some error codes, yet neither are they reported as an invalid error codes #19604

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--enable-error-code code does not enable some error codes, yet neither are they reported as an invalid error codes#19604
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bugmypy got something wrongtopic-configurationConfiguration files and flags

Description

@wyattscarpenter
wyattscarpenter
opened on Aug 7, 2025

In my understanding, --enable-error-code unreachable should have the same effect as --warn-unreachable. But, instead, it seems to have no effect, and doesn't even produce an error.

$uvx mypy -c "if False: print('hello')"
Success: no issues found in 1 source file

$uvx mypy -c "if False: print('hello')" --warn-unreachable
<string>:1: error: Statement is unreachable  [unreachable]
Found 1 error in 1 file (checked 1 source file)

$uvx mypy -c "if False: print('hello')" --enable-error-code unreachable
Success: no issues found in 1 source file

$uvx mypy -c "if False: print('hello')" --enable-error-code unreachable --warn-unreachable
<string>:1: error: Statement is unreachable  [unreachable]
Found 1 error in 1 file (checked 1 source file)

$uvx mypy -c "if False: print('hello')" --enable-error-code funnyerrorcodenotreal
usage: mypy [-h] [-v] [-V] [more options; see below]
            [-m MODULE] [-p PACKAGE] [-c PROGRAM_TEXT] [files ...]
mypy: error: Invalid error code(s): funnyerrorcodenotreal

Based on my testing, this seems to have been the case since 1.0.0 and maybe before, and thus is not a recent regression.

Activity

  1. wyattscarpenter
    added
    bugmypy got something wrong
    on Aug 7, 2025
  2. wyattscarpenter
    changed the title [-]--enable-error-code unreachable does not enable unreachability analysis, yet neither is it reported as an invalid error code[/-] [+]`--enable-error-code unreachable` does not enable unreachability analysis, yet neither is it reported as an invalid error code (etc)[/+] on Aug 7, 2025

  3. wyattscarpenter commented on Aug 7, 2025

    @wyattscarpenter
    wyattscarpenter
    on Aug 7, 2025
    ContributorAuthor

    Oh, the same thing is true about --warn-redundant-casts. And, I suspect, all error codes and flags like this.

    $uvx mypy -c "from typing import cast; cast(int, 1)" --warn-redundant-casts
<string>:1: error: Redundant cast to "int"  [redundant-cast]
Found 1 error in 1 file (checked 1 source file)

$uvx mypy -c "from typing import cast; cast(int, 1)" --enable-error-code redundant-cast
Success: no issues found in 1 source file

    If they aren't going to have any effect there should be an error message. (But, really, they should just have an effect!)

  4. sterliakov
    added
    topic-configurationConfiguration files and flags
    on Aug 7, 2025

  5. A5rocks commented on Aug 30, 2025

    @A5rocks
    A5rocks
    on Aug 30, 2025
    Collaborator

    (But, really, they should just have an effect!)

    Yeah we probably should have the flags enable certain error codes and then solely check those. There are a few flags that meaningfully change mypy's behavior in a way that error codes don't, but that should be limited! (Stuff like strict-optional)

  6. wyattscarpenter
    changed the title [-]`--enable-error-code unreachable` does not enable unreachability analysis, yet neither is it reported as an invalid error code (etc)[/-] [+]`--enable-error-code code` does not enable some error codes, yet neither are they reported as an invalid error codes[/+] on Oct 1, 2025
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