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Commit 64a99db

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Auto merge of #145582 - estebank:issue-107806, r=chenyukang
Detect missing `if let` or `let-else` During `let` binding parse error and encountering a block, detect if there is a likely missing `if` or `else`: ``` error: expected one of `.`, `;`, `?`, `else`, or an operator, found `{` --> $DIR/missing-if-let-or-let-else.rs:14:25 | LL | let Some(x) = foo() { | ^ expected one of `.`, `;`, `?`, `else`, or an operator | help: you might have meant to use `if let` | LL | if let Some(x) = foo() { | ++ help: alternatively, you might have meant to use `let else` | LL | let Some(x) = foo() else { | ++++ ``` Fix #107806.
2 parents cd60c60 + 3af81cf commit 64a99db

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4 files changed

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‎compiler/rustc_parse/src/lib.rs

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@@ -6,6 +6,7 @@
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#![feature(assert_matches)]
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#![feature(box_patterns)]
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#![feature(debug_closure_helpers)]
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#![feature(default_field_values)]
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#![feature(if_let_guard)]
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#![feature(iter_intersperse)]
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#![recursion_limit = "256"]

‎compiler/rustc_parse/src/parser/stmt.rs

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Original file line numberDiff line numberDiff line change
@@ -6,6 +6,7 @@ use ast::Label;
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use rustc_ast as ast;
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use rustc_ast::token::{self, Delimiter, InvisibleOrigin, MetaVarKind, TokenKind};
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use rustc_ast::util::classify::{self, TrailingBrace};
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use rustc_ast::visit::{Visitor, walk_expr};
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use rustc_ast::{
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AttrStyle, AttrVec, Block, BlockCheckMode, DUMMY_NODE_ID, Expr, ExprKind, HasAttrs, Local,
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LocalKind, MacCall, MacCallStmt, MacStmtStyle, Recovered, Stmt, StmtKind,
@@ -783,6 +784,100 @@ impl<'a> Parser<'a> {
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Ok(self.mk_block(stmts, s, lo.to(self.prev_token.span)))
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}
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fn recover_missing_let_else(&mut self, err: &mut Diag<'_>, pat: &ast::Pat, stmt_span: Span) {
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if self.token.kind != token::OpenBrace {
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return;
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}
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match pat.kind {
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ast::PatKind::Ident(..) | ast::PatKind::Missing | ast::PatKind::Wild => {
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// Not if let or let else
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return;
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}
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_ => {}
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}
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let snapshot = self.create_snapshot_for_diagnostic();
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let block_span = self.token.span;
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let (if_let, let_else) = match self.parse_block() {
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Ok(block) => {
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let mut idents = vec![];
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pat.walk(&mut |pat: &ast::Pat| {
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if let ast::PatKind::Ident(_, ident, _) = pat.kind {
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idents.push(ident);
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}
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true
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});
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struct IdentFinder {
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idents: Vec<Ident>,
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/// If a block references one of the bindings introduced by the let pattern,
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/// we likely meant to use `if let`.
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/// This is pre-expansion, so if we encounter
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/// `let Some(x) = foo() { println!("{x}") }` we won't find it.
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references_ident: bool = false,
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/// If a block has a `return`, then we know with high certainty that it was
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/// meant to be let-else.
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has_return: bool = false,
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}
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822+
impl<'a> Visitor<'a> for IdentFinder {
823+
fn visit_ident(&mut self, ident: &Ident) {
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for i in &self.idents {
825+
if ident.name == i.name {
826+
self.references_ident = true;
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}
828+
}
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}
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fn visit_expr(&mut self, node: &'a Expr) {
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if let ExprKind::Ret(..) = node.kind {
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self.has_return = true;
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}
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walk_expr(self, node);
835+
}
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}
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// Collect all bindings in pattern and see if they appear in the block. Likely meant
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// to write `if let`. See if the block has a return. Likely meant to write
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// `let else`.
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let mut visitor = IdentFinder { idents, .. };
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visitor.visit_block(&block);
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(visitor.references_ident, visitor.has_return)
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}
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Err(e) => {
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e.cancel();
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self.restore_snapshot(snapshot);
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(false, false)
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}
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};
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let mut alternatively = "";
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if if_let || !let_else {
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alternatively = "alternatively, ";
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err.span_suggestion_verbose(
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stmt_span.shrink_to_lo(),
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"you might have meant to use `if let`",
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"if ".to_string(),
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if if_let {
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Applicability::MachineApplicable
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} else {
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Applicability::MaybeIncorrect
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},
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);
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}
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if let_else || !if_let {
868+
err.span_suggestion_verbose(
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block_span.shrink_to_lo(),
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format!("{alternatively}you might have meant to use `let else`"),
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"else ".to_string(),
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if let_else {
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Applicability::MachineApplicable
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} else {
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Applicability::MaybeIncorrect
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},
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);
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}
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}
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786881
fn recover_missing_dot(&mut self, err: &mut Diag<'_>) {
787882
let Some((ident, _)) = self.token.ident() else {
788883
return;
@@ -977,6 +1072,7 @@ impl<'a> Parser<'a> {
9771072
self.check_mistyped_turbofish_with_multiple_type_params(e, expr).map_err(
9781073
|mut e| {
9791074
self.recover_missing_dot(&mut e);
1075+
self.recover_missing_let_else(&mut e, &local.pat, stmt.span);
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e
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},
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)?;
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@@ -0,0 +1,24 @@
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fn a() {
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let Some(x) = foo() { //~ ERROR expected one of
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//~^ HELP you might have meant to use `if let`
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let y = x;
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}
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}
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fn b() {
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let Some(x) = foo() { //~ ERROR expected one of
9+
//~^ HELP you might have meant to use `let else`
10+
return;
11+
}
12+
}
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fn c() {
14+
let Some(x) = foo() { //~ ERROR expected one of
15+
//~^ HELP you might have meant to use `if let`
16+
//~| HELP alternatively, you might have meant to use `let else`
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// The parser check happens pre-macro-expansion, so we don't know for sure.
18+
println!("{x}");
19+
}
20+
}
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fn foo() -> Option<i32> {
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Some(42)
23+
}
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fn main() {}
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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,39 @@
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error: expected one of `.`, `;`, `?`, `else`, or an operator, found `{`
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--> $DIR/missing-if-let-or-let-else.rs:2:25
3+
|
4+
LL | let Some(x) = foo() {
5+
| ^ expected one of `.`, `;`, `?`, `else`, or an operator
6+
|
7+
help: you might have meant to use `if let`
8+
|
9+
LL | if let Some(x) = foo() {
10+
| ++
11+
12+
error: expected one of `.`, `;`, `?`, `else`, or an operator, found `{`
13+
--> $DIR/missing-if-let-or-let-else.rs:8:25
14+
|
15+
LL | let Some(x) = foo() {
16+
| ^ expected one of `.`, `;`, `?`, `else`, or an operator
17+
|
18+
help: you might have meant to use `let else`
19+
|
20+
LL | let Some(x) = foo() else {
21+
| ++++
22+
23+
error: expected one of `.`, `;`, `?`, `else`, or an operator, found `{`
24+
--> $DIR/missing-if-let-or-let-else.rs:14:25
25+
|
26+
LL | let Some(x) = foo() {
27+
| ^ expected one of `.`, `;`, `?`, `else`, or an operator
28+
|
29+
help: you might have meant to use `if let`
30+
|
31+
LL | if let Some(x) = foo() {
32+
| ++
33+
help: alternatively, you might have meant to use `let else`
34+
|
35+
LL | let Some(x) = foo() else {
36+
| ++++
37+
38+
error: aborting due to 3 previous errors
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