bjoernager/rust
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Warn users about || in let chain expressions

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This commit is contained in:
Caio 2022-03-09 15:04:09 -03:00
parent 10dccdc7fc
commit 915f9a599c
3 changed files with 179 additions and 96 deletions
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104
compiler/rustc_ast_passes/src/ast_validation.rs
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@ -64,8 +64,8 @@ struct AstValidator<'a> {
/// certain positions.
is_assoc_ty_bound_banned: bool,
/// Used to allow `let` expressions in certain syntactic locations.
is_let_allowed: bool,
/// See [ForbiddenLetReason]
forbidden_let_reason: Option<ForbiddenLetReason>,
lint_buffer: &'a mut LintBuffer,
}
@ -103,20 +103,28 @@ impl<'a> AstValidator<'a> {
self.is_tilde_const_allowed = old;
}
fn with_let_allowed(&mut self, allowed: bool, f: impl FnOnce(&mut Self, bool)) {
let old = mem::replace(&mut self.is_let_allowed, allowed);
fn with_let_management(
&mut self,
forbidden_let_reason: Option<ForbiddenLetReason>,
f: impl FnOnce(&mut Self, Option<ForbiddenLetReason>),
) {
let old = mem::replace(&mut self.forbidden_let_reason, forbidden_let_reason);
f(self, old);
self.is_let_allowed = old;
self.forbidden_let_reason = old;
}
/// Emits an error banning the `let` expression provided in the given location.
fn ban_let_expr(&self, expr: &'a Expr) {
fn ban_let_expr(&self, expr: &'a Expr, forbidden_let_reason: ForbiddenLetReason) {
let sess = &self.session;
if sess.opts.unstable_features.is_nightly_build() {
sess.struct_span_err(expr.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 parentheses in those conditions")
.emit();
let err = "`let` expressions are not supported here";
let mut diag = sess.struct_span_err(expr.span, err);
diag.note("only supported directly in conditions of `if` and `while` expressions");
diag.note("as well as when nested within `&&` and parentheses in those conditions");
if let ForbiddenLetReason::ForbiddenWithOr(span) = forbidden_let_reason {
diag.span_note(span, "`||` operators are not allowed in let chain expressions");
}
diag.emit();
} else {
sess.struct_span_err(expr.span, "expected expression, found statement (`let`)")
.note("variable declaration using `let` is a statement")
@ -988,39 +996,48 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
}
fn visit_expr(&mut self, expr: &'a Expr) {
self.with_let_allowed(false, |this, let_allowed| match &expr.kind {
ExprKind::If(cond, then, opt_else) => {
this.visit_block(then);
walk_list!(this, visit_expr, opt_else);
this.with_let_allowed(true, |this, _| this.visit_expr(cond));
return;
}
ExprKind::Let(..) if !let_allowed => this.ban_let_expr(expr),
ExprKind::Match(expr, arms) => {
this.visit_expr(expr);
for arm in arms {
this.visit_expr(&arm.body);
this.visit_pat(&arm.pat);
walk_list!(this, visit_attribute, &arm.attrs);
if let Some(ref guard) = arm.guard {
if let ExprKind::Let(_, ref expr, _) = guard.kind {
this.with_let_allowed(true, |this, _| this.visit_expr(expr));
self.with_let_management(Some(ForbiddenLetReason::GenericForbidden), |this, forbidden_let_reason| {
match &expr.kind {
ExprKind::Binary(Spanned { node: BinOpKind::Or, span }, lhs, rhs) => {
let forbidden_let_reason = Some(ForbiddenLetReason::ForbiddenWithOr(*span));
this.with_let_management(forbidden_let_reason, |this, _| this.visit_expr(lhs));
this.with_let_management(forbidden_let_reason, |this, _| this.visit_expr(rhs));
}
ExprKind::If(cond, then, opt_else) => {
this.visit_block(then);
walk_list!(this, visit_expr, opt_else);
this.with_let_management(None, |this, _| this.visit_expr(cond));
return;
}
ExprKind::Let(..) if let Some(elem) = forbidden_let_reason => {
this.ban_let_expr(expr, elem);
},
ExprKind::Match(scrutinee, arms) => {
this.visit_expr(scrutinee);
for arm in arms {
this.visit_expr(&arm.body);
this.visit_pat(&arm.pat);
walk_list!(this, visit_attribute, &arm.attrs);
if let Some(guard) = &arm.guard && let ExprKind::Let(_, guard_expr, _) = &guard.kind {
this.with_let_management(None, |this, _| {
this.visit_expr(guard_expr)
});
return;
}
}
}
ExprKind::Paren(_) | ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, ..) => {
this.with_let_management(forbidden_let_reason, |this, _| visit::walk_expr(this, expr));
return;
}
ExprKind::While(cond, then, opt_label) => {
walk_list!(this, visit_label, opt_label);
this.visit_block(then);
this.with_let_management(None, |this, _| this.visit_expr(cond));
return;
}
_ => visit::walk_expr(this, expr),
}
ExprKind::Paren(_) | ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, ..) => {
this.with_let_allowed(let_allowed, |this, _| visit::walk_expr(this, expr));
return;
}
ExprKind::While(cond, then, opt_label) => {
walk_list!(this, visit_label, opt_label);
this.visit_block(then);
this.with_let_allowed(true, |this, _| this.visit_expr(cond));
return;
}
_ => visit::walk_expr(this, expr),
});
}
@ -1772,10 +1789,19 @@ pub fn check_crate(session: &Session, krate: &Crate, lints: &mut LintBuffer) ->
is_tilde_const_allowed: false,
is_impl_trait_banned: false,
is_assoc_ty_bound_banned: false,
is_let_allowed: false,
forbidden_let_reason: Some(ForbiddenLetReason::GenericForbidden),
lint_buffer: lints,
};
visit::walk_crate(&mut validator, krate);
validator.has_proc_macro_decls
}
/// Used to forbid `let` expressions in certain syntactic locations.
#[derive(Clone, Copy)]
enum ForbiddenLetReason {
/// A let chain with the `||` operator
ForbiddenWithOr(Span),
/// `let` is not valid and the source environment is not important
GenericForbidden,
}