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Currently, `tracing-attributes` generates a `let _ = ();` in between the
`if tracing::level_enabled!(...) {}` and the function body. This is
intended to suppress the `clippy::suspicious_else_formatting` lint,
which is generated when an `if` is followed immediately by a block with
no whitespace in between. Since we can't add whitespace in the generated
code (as `quote` produces a stream of _rust tokens_, not text), we
can't suppress the lint without adding a no-op statement.
However, unfortunately, the no-op let triggers a _different_ lint
(`clippy::let_unit_value`), when `clippy::pedantic` is enabled. This is
kind of annoying for some users.
This branch changes the code to suppress the
`suspicious_else_formatting` lint using `#[allow(...)]` attributes,
instead. The warning is turned back on inside of user code, since users
probably want the warning.
## Motivation The changes in #1607 introduced a potential compilation error when using the `#[instrument]` attribute on `async fn`s that return a type that includes a closure or is otherwise unnameable. This is because the future's body code was quoted in two separate places in order to have a separate branch when the span is statically disabled. This means that when a closure is returned, it will technically have two distinct types based on whether or not the span is enabled, since it originates from two separate source code locations (although `quote_spanned!` obscures this, so the compiler diagnostic will appear to have two closures originating from the same location). ## Solution This branch fixes this issue by changing the code generated for `#[instrument]`ed async functions. Unfortunately, for async functions, we can't have the optimization of not creating the span at all when the level is disabled, because we need to create the span _before_ creating the future, as it may borrow arguments. I've also added tests reproducing issue #1615 Fixes #1615
## Motivation Apparently, using `quote_spanned!` can trigger a Clippy bug where the text `else`, even inside a comment, _may_ cause the `suspicious_else_formatting` lint to be triggered incorrectly (see rust-lang/rust-clippy#7760 and rust-lang/rust-clippy#6249). This causes the lint to fire in some cases when the `#[instrument]` attribute is used on `async fn`s. See issue #1613 for details. ## Solution It turns out that some of the uses of `quote_spanned!` in the `tracing-attributes` code generation are not needed. We really only need `quote_spanned!` when actually interpolating the user provided code into a block, not in the `tracing-attributes` code that inserts the generated code for producing the span etc. Replacing some of these `quote_spanned!` uses with the normal `quote!` macro still generates correct location diagnostics for errors in the user code, but fixes the incorrect clippy lint. I've added a few test cases that should reproduce the bug. Fixes #1613 Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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this backports bugfixes for issues introduced in
tracing-attributesv0.1.17 frommastertov0.1.x. in particular, this includes:clippy::suspicious_elsewithout nop let (attributes: suppressclippy::suspicious_elsewithout nop let #1614)i'll rebase and merge this pending CI, since these changes were already approved on
master.