Comment by masklinn

3 years ago

Error-ing is the point here and what the period achieved. It’s a feature detection snippet so if it fails to compile the feature is disabled.

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masklinn

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rmast  3 years ago

It seems like there should be a way to catch these types of “bugs” - some form of dynamic analysis tool that extracts the feature detection code snippets and tries to compile them; if they fail for something like a syntax error, flag it as a broken check.

Expanding macros on different OSes could complicate things though, and determining what flags to build the feature check code with — so perhaps filtering based on the type of error would be best done as part of the build system functionality for doing the feature checking.

  • humanrebar  3 years ago

    I'd prefer if the ecosystem standardized on some dependency management primitives so critical projects aren't expected to invent buggy and insecure hacks ("does this strong parse?") in order to accurately add dependencies.

    • rmast  3 years ago

      It would be interesting to see what the most common compile feature checks are for, and see what alternative ways could be used to make the same information available to a build system — it seems like any solution that requires libraries being updated to “export” information on the features they provide would have difficulties getting adoption (and not be backwards compatible with older versions of desired dependencies).

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  • masklinn  3 years ago

    > if they fail for something like a syntax error, flag it as a broken check.

    A syntax error might be exactly what they’re looking for e.g. they’re feature testing a new bit of syntax or a compiler extension.

    > so perhaps filtering based on the type of error would be best done as part of the build system functionality for doing the feature checking.

    Which would require every compiler to have detailed, consistent, and machine-readable failure reporting.

    • rmast  3 years ago

      At least for newer C++ standards it seems like there is decent support for feature test macros, which could reduce the need for a feature check involving compiling a snippet of test code to decide if a feature is available: https://en.cppreference.com/w/cpp/feature_test

      Handling the output from several of the most recent GCC and Clang versions would probably cover the majority of cases, and add in MSVC for Windows. If the output isn’t from a recognized compiler or doesn’t match expectations, the only option is falling back to current behavior. Not ideal, but better than the current status quo…

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