bjoernager/rust
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Account for if (let pat = expr) {}

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Partially address #82827.
This commit is contained in:
Esteban Küber 2021-03-06 18:29:41 -08:00
parent 1c77a1fa3c
commit e62a543344
8 changed files with 216 additions and 231 deletions
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49
compiler/rustc_ast_lowering/src/expr.rs
View file

@ -97,6 +97,23 @@ impl<'hir> LoweringContext<'_, 'hir> {
ExprKind::Let(ref pat, ref scrutinee) => {
self.lower_expr_if_let(e.span, pat, scrutinee, then, else_opt.as_deref())
}
ExprKind::Paren(ref paren) => match paren.peel_parens().kind {
ExprKind::Let(ref pat, ref scrutinee) => {
// A user has written `if (let Some(x) = foo) {`, we want to avoid
// confusing them with mentions of nightly features.
// If this logic is changed, you will also likely need to touch
// `unused::UnusedParens::check_expr`.
self.if_let_expr_with_parens(cond, &paren.peel_parens());
self.lower_expr_if_let(
e.span,
pat,
scrutinee,
then,
else_opt.as_deref(),
)
}
_ => self.lower_expr_if(cond, then, else_opt.as_deref()),
},
_ => self.lower_expr_if(cond, then, else_opt.as_deref()),
},
ExprKind::While(ref cond, ref body, opt_label) => self
@ -346,6 +363,32 @@ impl<'hir> LoweringContext<'_, 'hir> {
hir::ExprKind::Call(f, self.lower_exprs(&real_args))
}
fn if_let_expr_with_parens(&mut self, cond: &Expr, paren: &Expr) {
let start = cond.span.until(paren.span);
let end = paren.span.shrink_to_hi().until(cond.span.shrink_to_hi());
let mut err = self.sess.struct_span_err(
vec![start, end],
"invalid parentheses around `let` expression in `if let`",
);
if self.sess.opts.unstable_features.is_nightly_build() {
err.note(
"only supported directly without parentheses in conditions of `if`- and \
`while`-expressions, as well as in `let` chains within parentheses",
);
} else {
err.note("variable declaration using `let` is a statement, not a condition");
}
err.multipart_suggestion(
"`if let` needs to be written without parentheses",
vec![(start, String::new()), (end, String::new())],
rustc_errors::Applicability::MachineApplicable,
);
err.emit();
// Ideally, we'd remove the feature gating of a `let` expression since we are already
// complaining about it here, but `feature_gate::check_crate` has already run by now:
// self.sess.parse_sess.gated_spans.ungate_last(sym::let_chains, paren.span);
}
/// Emit an error and lower `ast::ExprKind::Let(pat, scrutinee)` into:
/// ```rust
/// match scrutinee { pats => true, _ => false }
@ -356,8 +399,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
if self.sess.opts.unstable_features.is_nightly_build() {
self.sess
.struct_span_err(span, "`let` expressions are not supported here")
.note("only supported directly in conditions of `if`- and `while`-expressions")
.note("as well as when nested within `&&` and parenthesis in those conditions")
.note(
"only supported directly without parentheses in conditions of `if`- and \
`while`-expressions, as well as in `let` chains within parentheses",
)
.emit();
} else {
self.sess