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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:03:36 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:03:36 +0000 |
commit | 17d40c6057c88f4c432b0d7bac88e1b84cb7e67f (patch) | |
tree | 3f66c4a5918660bb8a758ab6cda5ff8ee4f6cdcd /src/tools/clippy/src/docs/trivially_copy_pass_by_ref.txt | |
parent | Adding upstream version 1.64.0+dfsg1. (diff) | |
download | rustc-upstream/1.65.0+dfsg1.tar.xz rustc-upstream/1.65.0+dfsg1.zip |
Adding upstream version 1.65.0+dfsg1.upstream/1.65.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/tools/clippy/src/docs/trivially_copy_pass_by_ref.txt')
-rw-r--r-- | src/tools/clippy/src/docs/trivially_copy_pass_by_ref.txt | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/src/tools/clippy/src/docs/trivially_copy_pass_by_ref.txt b/src/tools/clippy/src/docs/trivially_copy_pass_by_ref.txt new file mode 100644 index 000000000..f54cce5e2 --- /dev/null +++ b/src/tools/clippy/src/docs/trivially_copy_pass_by_ref.txt @@ -0,0 +1,43 @@ +### What it does +Checks for functions taking arguments by reference, where +the argument type is `Copy` and small enough to be more efficient to always +pass by value. + +### Why is this bad? +In many calling conventions instances of structs will +be passed through registers if they fit into two or less general purpose +registers. + +### Known problems +This lint is target register size dependent, it is +limited to 32-bit to try and reduce portability problems between 32 and +64-bit, but if you are compiling for 8 or 16-bit targets then the limit +will be different. + +The configuration option `trivial_copy_size_limit` can be set to override +this limit for a project. + +This lint attempts to allow passing arguments by reference if a reference +to that argument is returned. This is implemented by comparing the lifetime +of the argument and return value for equality. However, this can cause +false positives in cases involving multiple lifetimes that are bounded by +each other. + +Also, it does not take account of other similar cases where getting memory addresses +matters; namely, returning the pointer to the argument in question, +and passing the argument, as both references and pointers, +to a function that needs the memory address. For further details, refer to +[this issue](https://github.com/rust-lang/rust-clippy/issues/5953) +that explains a real case in which this false positive +led to an **undefined behavior** introduced with unsafe code. + +### Example + +``` +fn foo(v: &u32) {} +``` + +Use instead: +``` +fn foo(v: u32) {} +```
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