1
Fork 0

Rollup merge of #99696 - WaffleLapkin:uplift, r=fee1-dead

Uplift `clippy::for_loops_over_fallibles` lint into rustc

This PR, as the title suggests, uplifts [`clippy::for_loops_over_fallibles`] lint into rustc. This lint warns for code like this:
```rust
for _ in Some(1) {}
for _ in Ok::<_, ()>(1) {}
```
i.e. directly iterating over `Option` and `Result` using `for` loop.

There are a number of suggestions that this PR adds (on top of what clippy suggested):
1. If the argument (? is there a better name for that expression) of a `for` loop is a `.next()` call, then we can suggest removing it (or rather replacing with `.by_ref()` to allow iterator being used later)
   ```rust
    for _ in iter.next() {}
    // turns into
    for _ in iter.by_ref() {}
    ```
2. (otherwise) We can suggest using `while let`, this is useful for non-iterator, iterator-like things like [async] channels
   ```rust
   for _ in rx.recv() {}
   // turns into
   while let Some(_) = rx.recv() {}
   ```
3. If the argument type is `Result<impl IntoIterator, _>` and the body has a `Result<_, _>` type, we can suggest using `?`
   ```rust
   for _ in f() {}
   // turns into
   for _ in f()? {}
   ```
4. To preserve the original behavior and clear intent, we can suggest using `if let`
   ```rust
   for _ in f() {}
   // turns into
   if let Some(_) = f() {}
   ```
(P.S. `Some` and `Ok` are interchangeable depending on the type)

I still feel that the lint wording/look is somewhat off, so I'll be happy to hear suggestions (on how to improve suggestions :D)!

Resolves #99272

[`clippy::for_loops_over_fallibles`]: https://rust-lang.github.io/rust-clippy/master/index.html#for_loops_over_fallibles
This commit is contained in:
Dylan DPC 2022-10-10 13:43:40 +05:30 committed by GitHub
commit 7e16f9f1ea
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
26 changed files with 381 additions and 366 deletions

View file

@ -244,14 +244,12 @@ pub trait Visitor<'ast>: Sized {
#[macro_export]
macro_rules! walk_list {
($visitor: expr, $method: ident, $list: expr) => {
for elem in $list {
$visitor.$method(elem)
}
};
($visitor: expr, $method: ident, $list: expr, $($extra_args: expr),*) => {
for elem in $list {
$visitor.$method(elem, $($extra_args,)*)
($visitor: expr, $method: ident, $list: expr $(, $($extra_args: expr),* )?) => {
{
#[cfg_attr(not(bootstrap), allow(for_loops_over_fallibles))]
for elem in $list {
$visitor.$method(elem $(, $($extra_args,)* )?)
}
}
}
}

View file

@ -0,0 +1,183 @@
use crate::{LateContext, LateLintPass, LintContext};
use hir::{Expr, Pat};
use rustc_errors::{Applicability, DelayDm};
use rustc_hir as hir;
use rustc_infer::traits::TraitEngine;
use rustc_infer::{infer::TyCtxtInferExt, traits::ObligationCause};
use rustc_middle::ty::{self, List};
use rustc_span::{sym, Span};
use rustc_trait_selection::traits::TraitEngineExt;
declare_lint! {
/// The `for_loops_over_fallibles` lint checks for `for` loops over `Option` or `Result` values.
///
/// ### Example
///
/// ```rust
/// let opt = Some(1);
/// for x in opt { /* ... */}
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Both `Option` and `Result` implement `IntoIterator` trait, which allows using them in a `for` loop.
/// `for` loop over `Option` or `Result` will iterate either 0 (if the value is `None`/`Err(_)`)
/// or 1 time (if the value is `Some(_)`/`Ok(_)`). This is not very useful and is more clearly expressed
/// via `if let`.
///
/// `for` loop can also be accidentally written with the intention to call a function multiple times,
/// while the function returns `Some(_)`, in these cases `while let` loop should be used instead.
///
/// The "intended" use of `IntoIterator` implementations for `Option` and `Result` is passing them to
/// generic code that expects something implementing `IntoIterator`. For example using `.chain(option)`
/// to optionally add a value to an iterator.
pub FOR_LOOPS_OVER_FALLIBLES,
Warn,
"for-looping over an `Option` or a `Result`, which is more clearly expressed as an `if let`"
}
declare_lint_pass!(ForLoopsOverFallibles => [FOR_LOOPS_OVER_FALLIBLES]);
impl<'tcx> LateLintPass<'tcx> for ForLoopsOverFallibles {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
let Some((pat, arg)) = extract_for_loop(expr) else { return };
let ty = cx.typeck_results().expr_ty(arg);
let &ty::Adt(adt, substs) = ty.kind() else { return };
let (article, ty, var) = match adt.did() {
did if cx.tcx.is_diagnostic_item(sym::Option, did) => ("an", "Option", "Some"),
did if cx.tcx.is_diagnostic_item(sym::Result, did) => ("a", "Result", "Ok"),
_ => return,
};
let msg = DelayDm(|| {
format!(
"for loop over {article} `{ty}`. This is more readably written as an `if let` statement",
)
});
cx.struct_span_lint(FOR_LOOPS_OVER_FALLIBLES, arg.span, msg, |lint| {
if let Some(recv) = extract_iterator_next_call(cx, arg)
&& let Ok(recv_snip) = cx.sess().source_map().span_to_snippet(recv.span)
{
lint.span_suggestion(
recv.span.between(arg.span.shrink_to_hi()),
format!("to iterate over `{recv_snip}` remove the call to `next`"),
".by_ref()",
Applicability::MaybeIncorrect
);
} else {
lint.multipart_suggestion_verbose(
format!("to check pattern in a loop use `while let`"),
vec![
// NB can't use `until` here because `expr.span` and `pat.span` have different syntax contexts
(expr.span.with_hi(pat.span.lo()), format!("while let {var}(")),
(pat.span.between(arg.span), format!(") = ")),
],
Applicability::MaybeIncorrect
);
}
if suggest_question_mark(cx, adt, substs, expr.span) {
lint.span_suggestion(
arg.span.shrink_to_hi(),
"consider unwrapping the `Result` with `?` to iterate over its contents",
"?",
Applicability::MaybeIncorrect,
);
}
lint.multipart_suggestion_verbose(
"consider using `if let` to clear intent",
vec![
// NB can't use `until` here because `expr.span` and `pat.span` have different syntax contexts
(expr.span.with_hi(pat.span.lo()), format!("if let {var}(")),
(pat.span.between(arg.span), format!(") = ")),
],
Applicability::MaybeIncorrect,
)
})
}
}
fn extract_for_loop<'tcx>(expr: &Expr<'tcx>) -> Option<(&'tcx Pat<'tcx>, &'tcx Expr<'tcx>)> {
if let hir::ExprKind::DropTemps(e) = expr.kind
&& let hir::ExprKind::Match(iterexpr, [arm], hir::MatchSource::ForLoopDesugar) = e.kind
&& let hir::ExprKind::Call(_, [arg]) = iterexpr.kind
&& let hir::ExprKind::Loop(block, ..) = arm.body.kind
&& let [stmt] = block.stmts
&& let hir::StmtKind::Expr(e) = stmt.kind
&& let hir::ExprKind::Match(_, [_, some_arm], _) = e.kind
&& let hir::PatKind::Struct(_, [field], _) = some_arm.pat.kind
{
Some((field.pat, arg))
} else {
None
}
}
fn extract_iterator_next_call<'tcx>(
cx: &LateContext<'_>,
expr: &Expr<'tcx>,
) -> Option<&'tcx Expr<'tcx>> {
// This won't work for `Iterator::next(iter)`, is this an issue?
if let hir::ExprKind::MethodCall(_, recv, _, _) = expr.kind
&& cx.typeck_results().type_dependent_def_id(expr.hir_id) == cx.tcx.lang_items().next_fn()
{
Some(recv)
} else {
return None
}
}
fn suggest_question_mark<'tcx>(
cx: &LateContext<'tcx>,
adt: ty::AdtDef<'tcx>,
substs: &List<ty::GenericArg<'tcx>>,
span: Span,
) -> bool {
let Some(body_id) = cx.enclosing_body else { return false };
let Some(into_iterator_did) = cx.tcx.get_diagnostic_item(sym::IntoIterator) else { return false };
if !cx.tcx.is_diagnostic_item(sym::Result, adt.did()) {
return false;
}
// Check that the function/closure/constant we are in has a `Result` type.
// Otherwise suggesting using `?` may not be a good idea.
{
let ty = cx.typeck_results().expr_ty(&cx.tcx.hir().body(body_id).value);
let ty::Adt(ret_adt, ..) = ty.kind() else { return false };
if !cx.tcx.is_diagnostic_item(sym::Result, ret_adt.did()) {
return false;
}
}
let ty = substs.type_at(0);
let infcx = cx.tcx.infer_ctxt().build();
let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx);
let cause = ObligationCause::new(
span,
body_id.hir_id,
rustc_infer::traits::ObligationCauseCode::MiscObligation,
);
fulfill_cx.register_bound(
&infcx,
ty::ParamEnv::empty(),
// Erase any region vids from the type, which may not be resolved
infcx.tcx.erase_regions(ty),
into_iterator_did,
cause,
);
// Select all, including ambiguous predicates
let errors = fulfill_cx.select_all_or_error(&infcx);
errors.is_empty()
}

View file

@ -52,6 +52,7 @@ mod early;
mod enum_intrinsics_non_enums;
mod errors;
mod expect;
mod for_loops_over_fallibles;
pub mod hidden_unicode_codepoints;
mod internal;
mod late;
@ -86,6 +87,7 @@ use rustc_span::Span;
use array_into_iter::ArrayIntoIter;
use builtin::*;
use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
use for_loops_over_fallibles::*;
use hidden_unicode_codepoints::*;
use internal::*;
use let_underscore::*;
@ -188,6 +190,7 @@ macro_rules! late_lint_mod_passes {
$macro!(
$args,
[
ForLoopsOverFallibles: ForLoopsOverFallibles,
HardwiredLints: HardwiredLints,
ImproperCTypesDeclarations: ImproperCTypesDeclarations,
ImproperCTypesDefinitions: ImproperCTypesDefinitions,