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Auto merge of rust-lang#102875 - Dylan-DPC:rollup-zwcq8h9, r=Dylan-DPC
Rollup of 6 pull requests Successful merges: - rust-lang#99696 (Uplift `clippy::for_loops_over_fallibles` lint into rustc) - rust-lang#102055 (Move some tests to more reasonable directories) - rust-lang#102786 (Remove tuple candidate, nothing special about it) - rust-lang#102794 (Make tests capture the error printed by a Result return) - rust-lang#102853 (Skip chained OpaqueCast when building captures.) - rust-lang#102868 (Rename `AssocItemKind::TyAlias` to `AssocItemKind::Type`) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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Original file line number | Diff line number | Diff line change |
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use crate::{LateContext, LateLintPass, LintContext}; | ||
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||
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; | ||
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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`" | ||
} | ||
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declare_lint_pass!(ForLoopsOverFallibles => [FOR_LOOPS_OVER_FALLIBLES]); | ||
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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 }; | ||
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let ty = cx.typeck_results().expr_ty(arg); | ||
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let &ty::Adt(adt, substs) = ty.kind() else { return }; | ||
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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, | ||
}; | ||
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let msg = DelayDm(|| { | ||
format!( | ||
"for loop over {article} `{ty}`. This is more readably written as an `if let` statement", | ||
) | ||
}); | ||
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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 | ||
); | ||
} | ||
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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, | ||
); | ||
} | ||
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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, | ||
) | ||
}) | ||
} | ||
} | ||
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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 | ||
} | ||
} | ||
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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 | ||
} | ||
} | ||
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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 }; | ||
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if !cx.tcx.is_diagnostic_item(sym::Result, adt.did()) { | ||
return false; | ||
} | ||
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// 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; | ||
} | ||
} | ||
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let ty = substs.type_at(0); | ||
let infcx = cx.tcx.infer_ctxt().build(); | ||
let mut fulfill_cx = <dyn TraitEngine<'_>>::new(infcx.tcx); | ||
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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, | ||
); | ||
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// Select all, including ambiguous predicates | ||
let errors = fulfill_cx.select_all_or_error(&infcx); | ||
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errors.is_empty() | ||
} |
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