bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Auto merge of #115677 - matthewjasper:let-expr-recovery, r=b-naber

Browse source 
Improve invalid let expression handling

- Move all of the checks for valid let expression positions to parsing.
- Add a field to ExprKind::Let in AST/HIR to mark whether it's in a valid location.
- Suppress some later errors and MIR construction for invalid let expressions.
- Fix a (drop) scope issue that was also responsible for #104172.

Fixes #104172
Fixes #104868
This commit is contained in:
bors 2023-09-14 19:56:55 +00:00
commit dac91a82e1
48 changed files with 2475 additions and 2287 deletions
Download patch file Download diff file Expand all files Collapse all files

4
compiler/rustc_ast/src/ast.rs
View file

@ -33,7 +33,7 @@ use rustc_macros::HashStable_Generic;
use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
use rustc_span::source_map::{respan, Spanned};
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::{Span, DUMMY_SP};
use rustc_span::{ErrorGuaranteed, Span, DUMMY_SP};
use std::fmt;
use std::mem;
use thin_vec::{thin_vec, ThinVec};
@ -1426,7 +1426,7 @@ pub enum ExprKind {
/// of `if` / `while` expressions. (e.g., `if let 0 = x { .. }`).
///
/// `Span` represents the whole `let pat = expr` statement.
Let(P<Pat>, P<Expr>, Span),
Let(P<Pat>, P<Expr>, Span, Option<ErrorGuaranteed>),
/// An `if` block, with an optional `else` block.
///
/// `if expr { block } else { expr }`

2
compiler/rustc_ast/src/mut_visit.rs
View file

@ -1366,7 +1366,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
vis.visit_ty(ty);
}
ExprKind::AddrOf(_, _, ohs) => vis.visit_expr(ohs),
ExprKind::Let(pat, scrutinee, _) => {
ExprKind::Let(pat, scrutinee, _, _) => {
vis.visit_pat(pat);
vis.visit_expr(scrutinee);
}

2
compiler/rustc_ast/src/util/classify.rs
View file

@ -36,7 +36,7 @@ pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<&ast::Expr> {
| AssignOp(_, _, e)
| Binary(_, _, e)
| Break(_, Some(e))
| Let(_, e, _)
| Let(_, e, _, _)
| Range(_, Some(e), _)
| Ret(Some(e))
| Unary(_, e)

2
compiler/rustc_ast/src/visit.rs
View file

@ -827,7 +827,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
visitor.visit_expr(subexpression);
visitor.visit_ty(typ)
}
ExprKind::Let(pat, expr, _) => {
ExprKind::Let(pat, expr, _, _) => {
visitor.visit_pat(pat);
visitor.visit_expr(expr);
}

6
compiler/rustc_ast_lowering/src/expr.rs
View file

@ -152,13 +152,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
let ohs = self.lower_expr(ohs);
hir::ExprKind::AddrOf(*k, *m, ohs)
}
ExprKind::Let(pat, scrutinee, span) => {
ExprKind::Let(pat, scrutinee, span, is_recovered) => {
hir::ExprKind::Let(self.arena.alloc(hir::Let {
hir_id: self.next_id(),
span: self.lower_span(*span),
pat: self.lower_pat(pat),
ty: None,
init: self.lower_expr(scrutinee),
is_recovered: *is_recovered,
}))
}
ExprKind::If(cond, then, else_opt) => {
@ -558,13 +559,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
fn lower_arm(&mut self, arm: &Arm) -> hir::Arm<'hir> {
let pat = self.lower_pat(&arm.pat);
let guard = arm.guard.as_ref().map(|cond| {
if let ExprKind::Let(pat, scrutinee, span) = &cond.kind {
if let ExprKind::Let(pat, scrutinee, span, is_recovered) = &cond.kind {
hir::Guard::IfLet(self.arena.alloc(hir::Let {
hir_id: self.next_id(),
span: self.lower_span(*span),
pat: self.lower_pat(pat),
ty: None,
init: self.lower_expr(scrutinee),
is_recovered: *is_recovered,
}))
} else {
hir::Guard::If(self.lower_expr(cond))

10
compiler/rustc_ast_passes/messages.ftl
View file

@ -117,16 +117,6 @@ ast_passes_forbidden_default =
`default` is only allowed on items in trait impls
.label = `default` because of this
ast_passes_forbidden_let =
`let` expressions are not supported here
.note = only supported directly in conditions of `if` and `while` expressions
.not_supported_or = `||` operators are not supported in let chain expressions
.not_supported_parentheses = `let`s wrapped in parentheses are not supported in a context with let chains
ast_passes_forbidden_let_stable =
expected expression, found statement (`let`)
.note = variable declaration using `let` is a statement
ast_passes_forbidden_lifetime_bound =
lifetime bounds cannot be used in this context

103
compiler/rustc_ast_passes/src/ast_validation.rs
View file

@ -14,14 +14,12 @@ use rustc_ast::{walk_list, StaticItem};
use rustc_ast_pretty::pprust::{self, State};
use rustc_data_structures::fx::FxIndexMap;
use rustc_feature::Features;
use rustc_macros::Subdiagnostic;
use rustc_parse::validate_attr;
use rustc_session::lint::builtin::{
DEPRECATED_WHERE_CLAUSE_LOCATION, MISSING_ABI, PATTERNS_IN_FNS_WITHOUT_BODY,
};
use rustc_session::lint::{BuiltinLintDiagnostics, LintBuffer};
use rustc_session::Session;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{kw, sym, Ident};
use rustc_span::Span;
use rustc_target::spec::abi;
@ -69,9 +67,6 @@ struct AstValidator<'a> {
/// or `Foo::Bar<impl Trait>`
is_impl_trait_banned: bool,
/// See [ForbiddenLetReason]
forbidden_let_reason: Option<ForbiddenLetReason>,
lint_buffer: &'a mut LintBuffer,
}
@ -118,26 +113,6 @@ impl<'a> AstValidator<'a> {
self.with_tilde_const(Some(ctx), f)
}
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.forbidden_let_reason = old;
}
/// Emits an error banning the `let` expression provided in the given location.
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.emit_err(errors::ForbiddenLet { span: expr.span, reason: forbidden_let_reason });
} else {
sess.emit_err(errors::ForbiddenLetStable { span: expr.span });
}
}
fn check_type_alias_where_clause_location(
&mut self,
ty_alias: &TyAlias,
@ -779,67 +754,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
validate_attr::check_attr(&self.session.parse_sess, attr);
}
fn visit_expr(&mut self, expr: &'a 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 local_reason = Some(ForbiddenLetReason::NotSupportedOr(*span));
this.with_let_management(local_reason, |this, _| this.visit_expr(lhs));
this.with_let_management(local_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 {
this.with_let_management(None, |this, _| {
this.visit_expr(guard)
});
}
}
}
ExprKind::Paren(local_expr) => {
fn has_let_expr(expr: &Expr) -> bool {
match &expr.kind {
ExprKind::Binary(_, lhs, rhs) => has_let_expr(lhs) || has_let_expr(rhs),
ExprKind::Let(..) => true,
_ => false,
}
}
let local_reason = if has_let_expr(local_expr) {
Some(ForbiddenLetReason::NotSupportedParentheses(local_expr.span))
}
else {
forbidden_let_reason
};
this.with_let_management(local_reason, |this, _| this.visit_expr(local_expr));
}
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),
}
});
}
fn visit_ty(&mut self, ty: &'a Ty) {
self.visit_ty_common(ty);
self.deny_anon_struct_or_union(ty);
@ -1601,26 +1515,9 @@ pub fn check_crate(
outer_impl_trait: None,
disallow_tilde_const: None,
is_impl_trait_banned: 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, Subdiagnostic)]
pub(crate) enum ForbiddenLetReason {
/// `let` is not valid and the source environment is not important
GenericForbidden,
/// A let chain with the `||` operator
#[note(ast_passes_not_supported_or)]
NotSupportedOr(#[primary_span] Span),
/// A let chain with invalid parentheses
///
/// For example, `let 1 = 1 && (expr && expr)` is allowed
/// but `(let 1 = 1 && (let 1 = 1 && (let 1 = 1))) && let a = 1` is not
#[note(ast_passes_not_supported_parentheses)]
NotSupportedParentheses(#[primary_span] Span),
}

19
compiler/rustc_ast_passes/src/errors.rs
View file

@ -5,27 +5,8 @@ use rustc_errors::AddToDiagnostic;
use rustc_macros::{Diagnostic, Subdiagnostic};
use rustc_span::{symbol::Ident, Span, Symbol};
use crate::ast_validation::ForbiddenLetReason;
use crate::fluent_generated as fluent;
#[derive(Diagnostic)]
#[diag(ast_passes_forbidden_let)]
#[note]
pub struct ForbiddenLet {
#[primary_span]
pub span: Span,
#[subdiagnostic]
pub(crate) reason: ForbiddenLetReason,
}
#[derive(Diagnostic)]
#[diag(ast_passes_forbidden_let_stable)]
#[note]
pub struct ForbiddenLetStable {
#[primary_span]
pub span: Span,
}
#[derive(Diagnostic)]
#[diag(ast_passes_keyword_lifetime)]
pub struct KeywordLifetime {

2
compiler/rustc_ast_pretty/src/pprust/state/expr.rs
View file

@ -352,7 +352,7 @@ impl<'a> State<'a> {
self.end();
self.word(")");
}
ast::ExprKind::Let(pat, scrutinee, _) => {
ast::ExprKind::Let(pat, scrutinee, _, _) => {
self.print_let(pat, scrutinee);
}
ast::ExprKind::If(test, blk, elseopt) => self.print_if(test, blk, elseopt.as_deref()),

2
compiler/rustc_builtin_macros/src/assert/context.rs
View file

@ -241,7 +241,7 @@ impl<'cx, 'a> Context<'cx, 'a> {
self.manage_cond_expr(prefix);
self.manage_cond_expr(suffix);
}
ExprKind::Let(_, local_expr, _) => {
ExprKind::Let(_, local_expr, _, _) => {
self.manage_cond_expr(local_expr);
}
ExprKind::Match(local_expr, _) => {

4
compiler/rustc_hir/src/hir.rs
View file

@ -19,6 +19,7 @@ use rustc_macros::HashStable_Generic;
use rustc_span::hygiene::MacroKind;
use rustc_span::source_map::Spanned;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
use rustc_span::ErrorGuaranteed;
use rustc_span::{def_id::LocalDefId, BytePos, Span, DUMMY_SP};
use rustc_target::asm::InlineAsmRegOrRegClass;
use rustc_target::spec::abi::Abi;
@ -1415,6 +1416,9 @@ pub struct Let<'hir> {
pub pat: &'hir Pat<'hir>,
pub ty: Option<&'hir Ty<'hir>>,
pub init: &'hir Expr<'hir>,
/// `Some` when this let expressions is not in a syntanctically valid location.
/// Used to prevent building MIR in such situations.
pub is_recovered: Option<ErrorGuaranteed>,
}
#[derive(Debug, Clone, Copy, HashStable_Generic)]

6
compiler/rustc_hir_analysis/src/check/region.rs
View file

@ -149,7 +149,7 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
// From now on, we continue normally.
visitor.cx = prev_cx;
}
hir::StmtKind::Local(..) | hir::StmtKind::Item(..) => {
hir::StmtKind::Local(..) => {
// Each declaration introduces a subscope for bindings
// introduced by the declaration; this subscope covers a
// suffix of the block. Each subscope in a block has the
@ -163,6 +163,10 @@ fn resolve_block<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, blk: &'tcx h
visitor.cx.var_parent = visitor.cx.parent;
visitor.visit_stmt(statement)
}
hir::StmtKind::Item(..) => {
// Don't create scopes for items, since they won't be
// lowered to THIR and MIR.
}
hir::StmtKind::Expr(..) | hir::StmtKind::Semi(..) => visitor.visit_stmt(statement),
}
}

7
compiler/rustc_hir_typeck/src/expr.rs
View file

@ -1203,7 +1203,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// otherwise check exactly as a let statement
self.check_decl(let_expr.into());
// but return a bool, for this is a boolean expression
self.tcx.types.bool
if let Some(error_guaranteed) = let_expr.is_recovered {
self.set_tainted_by_errors(error_guaranteed);
Ty::new_error(self.tcx, error_guaranteed)
} else {
self.tcx.types.bool
}
}
fn check_expr_loop(

2
compiler/rustc_hir_typeck/src/gather_locals.rs
View file

@ -50,7 +50,7 @@ impl<'a> From<&'a hir::Local<'a>> for Declaration<'a> {
impl<'a> From<&'a hir::Let<'a>> for Declaration<'a> {
fn from(let_expr: &'a hir::Let<'a>) -> Self {
let hir::Let { hir_id, pat, ty, span, init } = *let_expr;
let hir::Let { hir_id, pat, ty, span, init, is_recovered: _ } = *let_expr;
Declaration { hir_id, pat, ty, span, init: Some(init), origin: DeclOrigin::LetExpr }
}
}

12
compiler/rustc_lint/src/unused.rs
View file

@ -816,8 +816,7 @@ trait UnusedDelimLint {
let (value, ctx, followed_by_block, left_pos, right_pos, is_kw) = match e.kind {
// Do not lint `unused_braces` in `if let` expressions.
If(ref cond, ref block, _)
if !matches!(cond.kind, Let(_, _, _))
|| Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
if !matches!(cond.kind, Let(..)) || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
{
let left = e.span.lo() + rustc_span::BytePos(2);
let right = block.span.lo();
@ -826,8 +825,7 @@ trait UnusedDelimLint {
// Do not lint `unused_braces` in `while let` expressions.
While(ref cond, ref block, ..)
if !matches!(cond.kind, Let(_, _, _))
|| Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
if !matches!(cond.kind, Let(..)) || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
{
let left = e.span.lo() + rustc_span::BytePos(5);
let right = block.span.lo();
@ -1003,7 +1001,7 @@ impl UnusedDelimLint for UnusedParens {
self.emit_unused_delims_expr(cx, value, ctx, left_pos, right_pos, is_kw)
}
}
ast::ExprKind::Let(_, ref expr, _) => {
ast::ExprKind::Let(_, ref expr, _, _) => {
self.check_unused_delims_expr(
cx,
expr,
@ -1067,7 +1065,7 @@ impl EarlyLintPass for UnusedParens {
}
match e.kind {
ExprKind::Let(ref pat, _, _) | ExprKind::ForLoop(ref pat, ..) => {
ExprKind::Let(ref pat, _, _, _) | ExprKind::ForLoop(ref pat, ..) => {
self.check_unused_parens_pat(cx, pat, false, false, (true, true));
}
// We ignore parens in cases like `if (((let Some(0) = Some(1))))` because we already
@ -1311,7 +1309,7 @@ impl UnusedDelimLint for UnusedBraces {
}
}
}
ast::ExprKind::Let(_, ref expr, _) => {
ast::ExprKind::Let(_, ref expr, _, _) => {
self.check_unused_delims_expr(
cx,
expr,

3
compiler/rustc_parse/messages.ftl
View file

@ -196,6 +196,9 @@ parse_expected_else_block = expected `{"{"}`, found {$first_tok}
.suggestion = add an `if` if this is the condition of a chained `else if` statement
parse_expected_expression_found_let = expected expression, found `let` statement
.note = only supported directly in conditions of `if` and `while` expressions
.not_supported_or = `||` operators are not supported in let chain expressions
.not_supported_parentheses = `let`s wrapped in parentheses are not supported in a context with let chains
parse_expected_fn_path_found_fn_keyword = expected identifier, found keyword `fn`
.suggestion = use `Fn` to refer to the trait

5
compiler/rustc_parse/src/errors.rs
View file

@ -10,7 +10,7 @@ use rustc_span::symbol::Ident;
use rustc_span::{Span, Symbol};
use crate::fluent_generated as fluent;
use crate::parser::TokenDescription;
use crate::parser::{ForbiddenLetReason, TokenDescription};
#[derive(Diagnostic)]
#[diag(parse_maybe_report_ambiguous_plus)]
@ -392,9 +392,12 @@ pub(crate) struct IfExpressionMissingCondition {
#[derive(Diagnostic)]
#[diag(parse_expected_expression_found_let)]
#[note]
pub(crate) struct ExpectedExpressionFoundLet {
#[primary_span]
pub span: Span,
#[subdiagnostic]
pub reason: ForbiddenLetReason,
}
#[derive(Diagnostic)]

379
compiler/rustc_parse/src/parser/expr.rs
View file

@ -8,6 +8,7 @@ use super::{
use crate::errors;
use crate::maybe_recover_from_interpolated_ty_qpath;
use ast::mut_visit::{noop_visit_expr, MutVisitor};
use ast::{Path, PathSegment};
use core::mem;
use rustc_ast::ptr::P;
@ -27,6 +28,7 @@ use rustc_errors::{
AddToDiagnostic, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, IntoDiagnostic,
PResult, StashKey,
};
use rustc_macros::Subdiagnostic;
use rustc_session::errors::{report_lit_error, ExprParenthesesNeeded};
use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
use rustc_session::lint::BuiltinLintDiagnostics;
@ -122,8 +124,8 @@ impl<'a> Parser<'a> {
self.parse_expr().map(|value| AnonConst { id: DUMMY_NODE_ID, value })
}
fn parse_expr_catch_underscore(&mut self) -> PResult<'a, P<Expr>> {
match self.parse_expr() {
fn parse_expr_catch_underscore(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
match self.parse_expr_res(restrictions, None) {
Ok(expr) => Ok(expr),
Err(mut err) => match self.token.ident() {
Some((Ident { name: kw::Underscore, .. }, false))
@ -141,7 +143,8 @@ impl<'a> Parser<'a> {
/// Parses a sequence of expressions delimited by parentheses.
fn parse_expr_paren_seq(&mut self) -> PResult<'a, ThinVec<P<Expr>>> {
self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore()).map(|(r, _)| r)
self.parse_paren_comma_seq(|p| p.parse_expr_catch_underscore(Restrictions::empty()))
.map(|(r, _)| r)
}
/// Parses an expression, subject to the given restrictions.
@ -1345,110 +1348,113 @@ impl<'a> Parser<'a> {
// Outer attributes are already parsed and will be
// added to the return value after the fact.
// Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
let lo = self.token.span;
if let token::Literal(_) = self.token.kind {
// This match arm is a special-case of the `_` match arm below and
// could be removed without changing functionality, but it's faster
// to have it here, especially for programs with large constants.
self.parse_expr_lit()
} else if self.check(&token::OpenDelim(Delimiter::Parenthesis)) {
self.parse_expr_tuple_parens()
} else if self.check(&token::OpenDelim(Delimiter::Brace)) {
self.parse_expr_block(None, lo, BlockCheckMode::Default)
} else if self.check(&token::BinOp(token::Or)) || self.check(&token::OrOr) {
self.parse_expr_closure().map_err(|mut err| {
// If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
// then suggest parens around the lhs.
if let Some(sp) = self.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
}
err
})
} else if self.check(&token::OpenDelim(Delimiter::Bracket)) {
self.parse_expr_array_or_repeat(Delimiter::Bracket)
} else if self.is_builtin() {
self.parse_expr_builtin()
} else if self.check_path() {
self.parse_expr_path_start()
} else if self.check_keyword(kw::Move)
|| self.check_keyword(kw::Static)
|| self.check_const_closure()
{
self.parse_expr_closure()
} else if self.eat_keyword(kw::If) {
self.parse_expr_if()
} else if self.check_keyword(kw::For) {
if self.choose_generics_over_qpath(1) {
self.parse_expr_closure()
} else {
assert!(self.eat_keyword(kw::For));
self.parse_expr_for(None, self.prev_token.span)
}
} else if self.eat_keyword(kw::While) {
self.parse_expr_while(None, self.prev_token.span)
} else if let Some(label) = self.eat_label() {
self.parse_expr_labeled(label, true)
} else if self.eat_keyword(kw::Loop) {
let sp = self.prev_token.span;
self.parse_expr_loop(None, self.prev_token.span).map_err(|mut err| {
err.span_label(sp, "while parsing this `loop` expression");
err
})
} else if self.eat_keyword(kw::Match) {
let match_sp = self.prev_token.span;
self.parse_expr_match().map_err(|mut err| {
err.span_label(match_sp, "while parsing this `match` expression");
err
})
} else if self.eat_keyword(kw::Unsafe) {
let sp = self.prev_token.span;
self.parse_expr_block(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
|mut err| {
err.span_label(sp, "while parsing this `unsafe` expression");
let restrictions = self.restrictions;
self.with_res(restrictions - Restrictions::ALLOW_LET, |this| {
// Note: when adding new syntax here, don't forget to adjust `TokenKind::can_begin_expr()`.
let lo = this.token.span;
if let token::Literal(_) = this.token.kind {
// This match arm is a special-case of the `_` match arm below and
// could be removed without changing functionality, but it's faster
// to have it here, especially for programs with large constants.
this.parse_expr_lit()
} else if this.check(&token::OpenDelim(Delimiter::Parenthesis)) {
this.parse_expr_tuple_parens(restrictions)
} else if this.check(&token::OpenDelim(Delimiter::Brace)) {
this.parse_expr_block(None, lo, BlockCheckMode::Default)
} else if this.check(&token::BinOp(token::Or)) || this.check(&token::OrOr) {
this.parse_expr_closure().map_err(|mut err| {
// If the input is something like `if a { 1 } else { 2 } | if a { 3 } else { 4 }`
// then suggest parens around the lhs.
if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&lo) {
err.subdiagnostic(ExprParenthesesNeeded::surrounding(*sp));
}
err
},
)
} else if self.check_inline_const(0) {
self.parse_const_block(lo.to(self.token.span), false)
} else if self.may_recover() && self.is_do_catch_block() {
self.recover_do_catch()
} else if self.is_try_block() {
self.expect_keyword(kw::Try)?;
self.parse_try_block(lo)
} else if self.eat_keyword(kw::Return) {
self.parse_expr_return()
} else if self.eat_keyword(kw::Continue) {
self.parse_expr_continue(lo)
} else if self.eat_keyword(kw::Break) {
self.parse_expr_break()
} else if self.eat_keyword(kw::Yield) {
self.parse_expr_yield()
} else if self.is_do_yeet() {
self.parse_expr_yeet()
} else if self.eat_keyword(kw::Become) {
self.parse_expr_become()
} else if self.check_keyword(kw::Let) {
self.parse_expr_let()
} else if self.eat_keyword(kw::Underscore) {
Ok(self.mk_expr(self.prev_token.span, ExprKind::Underscore))
} else if self.token.uninterpolated_span().at_least_rust_2018() {
// `Span:.at_least_rust_2018()` is somewhat expensive; don't get it repeatedly.
if self.check_keyword(kw::Async) {
if self.is_async_block() {
// Check for `async {` and `async move {`.
self.parse_async_block()
})
} else if this.check(&token::OpenDelim(Delimiter::Bracket)) {
this.parse_expr_array_or_repeat(Delimiter::Bracket)
} else if this.is_builtin() {
this.parse_expr_builtin()
} else if this.check_path() {
this.parse_expr_path_start()
} else if this.check_keyword(kw::Move)
|| this.check_keyword(kw::Static)
|| this.check_const_closure()
{
this.parse_expr_closure()
} else if this.eat_keyword(kw::If) {
this.parse_expr_if()
} else if this.check_keyword(kw::For) {
if this.choose_generics_over_qpath(1) {
this.parse_expr_closure()
} else {
self.parse_expr_closure()
assert!(this.eat_keyword(kw::For));
this.parse_expr_for(None, this.prev_token.span)
}
} else if this.eat_keyword(kw::While) {
this.parse_expr_while(None, this.prev_token.span)
} else if let Some(label) = this.eat_label() {
this.parse_expr_labeled(label, true)
} else if this.eat_keyword(kw::Loop) {
let sp = this.prev_token.span;
this.parse_expr_loop(None, this.prev_token.span).map_err(|mut err| {
err.span_label(sp, "while parsing this `loop` expression");
err
})
} else if this.eat_keyword(kw::Match) {
let match_sp = this.prev_token.span;
this.parse_expr_match().map_err(|mut err| {
err.span_label(match_sp, "while parsing this `match` expression");
err
})
} else if this.eat_keyword(kw::Unsafe) {
let sp = this.prev_token.span;
this.parse_expr_block(None, lo, BlockCheckMode::Unsafe(ast::UserProvided)).map_err(
|mut err| {
err.span_label(sp, "while parsing this `unsafe` expression");
err
},
)
} else if this.check_inline_const(0) {
this.parse_const_block(lo.to(this.token.span), false)
} else if this.may_recover() && this.is_do_catch_block() {
this.recover_do_catch()
} else if this.is_try_block() {
this.expect_keyword(kw::Try)?;
this.parse_try_block(lo)
} else if this.eat_keyword(kw::Return) {
this.parse_expr_return()
} else if this.eat_keyword(kw::Continue) {
this.parse_expr_continue(lo)
} else if this.eat_keyword(kw::Break) {
this.parse_expr_break()
} else if this.eat_keyword(kw::Yield) {
this.parse_expr_yield()
} else if this.is_do_yeet() {
this.parse_expr_yeet()
} else if this.eat_keyword(kw::Become) {
this.parse_expr_become()
} else if this.check_keyword(kw::Let) {
this.parse_expr_let(restrictions)
} else if this.eat_keyword(kw::Underscore) {
Ok(this.mk_expr(this.prev_token.span, ExprKind::Underscore))
} else if this.token.uninterpolated_span().at_least_rust_2018() {
// `Span:.at_least_rust_2018()` is somewhat expensive; don't get it repeatedly.
if this.check_keyword(kw::Async) {
if this.is_async_block() {
// Check for `async {` and `async move {`.
this.parse_async_block()
} else {
this.parse_expr_closure()
}
} else if this.eat_keyword(kw::Await) {
this.recover_incorrect_await_syntax(lo, this.prev_token.span)
} else {
this.parse_expr_lit()
}
} else if self.eat_keyword(kw::Await) {
self.recover_incorrect_await_syntax(lo, self.prev_token.span)
} else {
self.parse_expr_lit()
this.parse_expr_lit()
}
} else {
self.parse_expr_lit()
}
})
}
fn parse_expr_lit(&mut self) -> PResult<'a, P<Expr>> {
@ -1462,13 +1468,13 @@ impl<'a> Parser<'a> {
}
}
fn parse_expr_tuple_parens(&mut self) -> PResult<'a, P<Expr>> {
fn parse_expr_tuple_parens(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
let lo = self.token.span;
self.expect(&token::OpenDelim(Delimiter::Parenthesis))?;
let (es, trailing_comma) = match self.parse_seq_to_end(
&token::CloseDelim(Delimiter::Parenthesis),
SeqSep::trailing_allowed(token::Comma),
|p| p.parse_expr_catch_underscore(),
|p| p.parse_expr_catch_underscore(restrictions.intersection(Restrictions::ALLOW_LET)),
) {
Ok(x) => x,
Err(err) => {
@ -2231,7 +2237,8 @@ impl<'a> Parser<'a> {
let decl_hi = self.prev_token.span;
let mut body = match fn_decl.output {
FnRetTy::Default(_) => {
let restrictions = self.restrictions - Restrictions::STMT_EXPR;
let restrictions =
self.restrictions - Restrictions::STMT_EXPR - Restrictions::ALLOW_LET;
self.parse_expr_res(restrictions, None)?
}
_ => {
@ -2436,10 +2443,12 @@ impl<'a> Parser<'a> {
/// Parses the condition of a `if` or `while` expression.
fn parse_expr_cond(&mut self) -> PResult<'a, P<Expr>> {
let cond =
let mut cond =
self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?;
if let ExprKind::Let(..) = cond.kind {
CondChecker { parser: self, forbid_let_reason: None }.visit_expr(&mut cond);
if let ExprKind::Let(_, _, _, None) = cond.kind {
// Remove the last feature gating of a `let` expression since it's stable.
self.sess.gated_spans.ungate_last(sym::let_chains, cond.span);
}
@ -2448,18 +2457,15 @@ impl<'a> Parser<'a> {
}
/// Parses a `let $pat = $expr` pseudo-expression.
fn parse_expr_let(&mut self) -> PResult<'a, P<Expr>> {
// This is a *approximate* heuristic that detects if `let` chains are
// being parsed in the right position. It's approximate because it
// doesn't deny all invalid `let` expressions, just completely wrong usages.
let not_in_chain = !matches!(
self.prev_token.kind,
TokenKind::AndAnd | TokenKind::Ident(kw::If, _) | TokenKind::Ident(kw::While, _)
);
if !self.restrictions.contains(Restrictions::ALLOW_LET) || not_in_chain {
self.sess.emit_err(errors::ExpectedExpressionFoundLet { span: self.token.span });
}
fn parse_expr_let(&mut self, restrictions: Restrictions) -> PResult<'a, P<Expr>> {
let is_recovered = if !restrictions.contains(Restrictions::ALLOW_LET) {
Some(self.sess.emit_err(errors::ExpectedExpressionFoundLet {
span: self.token.span,
reason: ForbiddenLetReason::OtherForbidden,
}))
} else {
None
};
self.bump(); // Eat `let` token
let lo = self.prev_token.span;
let pat = self.parse_pat_allow_top_alt(
@ -2479,8 +2485,7 @@ impl<'a> Parser<'a> {
}
let expr = self.parse_expr_assoc_with(1 + prec_let_scrutinee_needs_par(), None.into())?;
let span = lo.to(expr.span);
self.sess.gated_spans.gate(sym::let_chains, span);
Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span)))
Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span, is_recovered)))
}
/// Parses an `else { ... }` expression (`else` token already eaten).
@ -2829,7 +2834,10 @@ impl<'a> Parser<'a> {
)?;
let guard = if this.eat_keyword(kw::If) {
let if_span = this.prev_token.span;
let cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
let mut cond = this.parse_expr_res(Restrictions::ALLOW_LET, None)?;
CondChecker { parser: this, forbid_let_reason: None }.visit_expr(&mut cond);
let (has_let_expr, does_not_have_bin_op) = check_let_expr(&cond);
if has_let_expr {
if does_not_have_bin_op {
@ -3414,3 +3422,130 @@ impl<'a> Parser<'a> {
})
}
}
/// Used to forbid `let` expressions in certain syntactic locations.
#[derive(Clone, Copy, Subdiagnostic)]
pub(crate) enum ForbiddenLetReason {
/// `let` is not valid and the source environment is not important
OtherForbidden,
/// A let chain with the `||` operator
#[note(parse_not_supported_or)]
NotSupportedOr(#[primary_span] Span),
/// A let chain with invalid parentheses
///
/// For example, `let 1 = 1 && (expr && expr)` is allowed
/// but `(let 1 = 1 && (let 1 = 1 && (let 1 = 1))) && let a = 1` is not
#[note(parse_not_supported_parentheses)]
NotSupportedParentheses(#[primary_span] Span),
}
/// Visitor to check for invalid/unstable use of `ExprKind::Let` that can't
/// easily be caught in parsing. For example:
///
/// ```rust,ignore (example)
/// // Only know that the let isn't allowed once the `||` token is reached
/// if let Some(x) = y || true {}
/// // Only know that the let isn't allowed once the second `=` token is reached.
/// if let Some(x) = y && z = 1 {}
/// ```
struct CondChecker<'a> {
parser: &'a Parser<'a>,
forbid_let_reason: Option<ForbiddenLetReason>,
}
impl MutVisitor for CondChecker<'_> {
fn visit_expr(&mut self, e: &mut P<Expr>) {
use ForbiddenLetReason::*;
let span = e.span;
match e.kind {
ExprKind::Let(_, _, _, ref mut is_recovered @ None) => {
if let Some(reason) = self.forbid_let_reason {
*is_recovered = Some(
self.parser
.sess
.emit_err(errors::ExpectedExpressionFoundLet { span, reason }),
);
} else {
self.parser.sess.gated_spans.gate(sym::let_chains, span);
}
}
ExprKind::Binary(Spanned { node: BinOpKind::And, .. }, _, _) => {
noop_visit_expr(e, self);
}
ExprKind::Binary(Spanned { node: BinOpKind::Or, span: or_span }, _, _)
if let None | Some(NotSupportedOr(_)) = self.forbid_let_reason =>
{
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(NotSupportedOr(or_span));
noop_visit_expr(e, self);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Paren(ref inner)
if let None | Some(NotSupportedParentheses(_)) = self.forbid_let_reason =>
{
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(NotSupportedParentheses(inner.span));
noop_visit_expr(e, self);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Unary(_, _)
| ExprKind::Await(_, _)
| ExprKind::Assign(_, _, _)
| ExprKind::AssignOp(_, _, _)
| ExprKind::Range(_, _, _)
| ExprKind::Try(_)
| ExprKind::AddrOf(_, _, _)
| ExprKind::Binary(_, _, _)
| ExprKind::Field(_, _)
| ExprKind::Index(_, _, _)
| ExprKind::Call(_, _)
| ExprKind::MethodCall(_)
| ExprKind::Tup(_)
| ExprKind::Paren(_) => {
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(OtherForbidden);
noop_visit_expr(e, self);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Cast(ref mut op, _)
| ExprKind::Type(ref mut op, _) => {
let forbid_let_reason = self.forbid_let_reason;
self.forbid_let_reason = Some(OtherForbidden);
self.visit_expr(op);
self.forbid_let_reason = forbid_let_reason;
}
ExprKind::Let(_, _, _, Some(_))
| ExprKind::Array(_)
| ExprKind::ConstBlock(_)
| ExprKind::Lit(_)
| ExprKind::If(_, _, _)
| ExprKind::While(_, _, _)
| ExprKind::ForLoop(_, _, _, _)
| ExprKind::Loop(_, _, _)
| ExprKind::Match(_, _)
| ExprKind::Closure(_)
| ExprKind::Block(_, _)
| ExprKind::Async(_, _)
| ExprKind::TryBlock(_)
| ExprKind::Underscore
| ExprKind::Path(_, _)
| ExprKind::Break(_, _)
| ExprKind::Continue(_)
| ExprKind::Ret(_)
| ExprKind::InlineAsm(_)
| ExprKind::OffsetOf(_, _)
| ExprKind::MacCall(_)
| ExprKind::Struct(_)
| ExprKind::Repeat(_, _)
| ExprKind::Yield(_)
| ExprKind::Yeet(_)
| ExprKind::Become(_)
| ExprKind::IncludedBytes(_)
| ExprKind::FormatArgs(_)
| ExprKind::Err => {
// These would forbid any let expressions they contain already.
}
}
}
}

1
compiler/rustc_parse/src/parser/mod.rs
View file

@ -13,6 +13,7 @@ mod ty;
use crate::lexer::UnmatchedDelim;
pub use attr_wrapper::AttrWrapper;
pub use diagnostics::AttemptLocalParseRecovery;
pub(crate) use expr::ForbiddenLetReason;
pub(crate) use item::FnParseMode;
pub use pat::{CommaRecoveryMode, RecoverColon, RecoverComma};
pub use path::PathStyle;

2
compiler/rustc_resolve/src/late.rs
View file

@ -4180,7 +4180,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
self.resolve_expr(e, Some(&expr));
}
ExprKind::Let(ref pat, ref scrutinee, _) => {
ExprKind::Let(ref pat, ref scrutinee, _, _) => {
self.visit_expr(scrutinee);
self.resolve_pattern_top(pat, PatternSource::Let);
}