rust-lang / rust-lang/rfcs

desired: lint to detect uses of int-fallback that flow to foreign varargs

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Description

See #951.

In particular, from that RFC

unsafe {
    printf("value: %d\n\0".as_ptr() as *const _, 1);
}

Note that the numeric argument doesn't have an inferable type and therefore it falls back to the integer-fallback type i32. In C such a literal would have type c_int which coincides with i32 on all supported platforms. However, this might not always be the case.

Therefore, we would like a warn-by-default lint that catches instances of the above.

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Research direction

Start by reading RFC issue #951 and the cited printf example to understand how integer fallback reaches foreign varargs. Define the lint's warning behavior for this pattern and verify that the example is diagnosed without introducing false positives; the payload does not name implementation files or tests.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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