Add suggestions for expressions in let patterns

ShE3py · ShE3py · commit 5e2c8eb0f8fd · 2024-07-01T20:36:13.000+02:00
diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
@@ -788,6 +788,10 @@ parse_unexpected_expr_in_pat_create_guard_sugg = check the value in an arm guard
 
 parse_unexpected_expr_in_pat_inline_const_sugg = wrap the expression in a inline const (requires `{"#"}![feature(inline_const_pat)]`)
 
+parse_unexpected_expr_in_pat_remove_let_sugg = remove this `let`
+
+parse_unexpected_expr_in_pat_replace_let_else_with_if_sugg = use an `if`
+
 parse_unexpected_expr_in_pat_update_guard_sugg = check the value in the arm guard
 
 parse_unexpected_if_with_if = unexpected `if` in the condition expression
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
@@ -2492,6 +2492,28 @@ pub(crate) struct UnexpectedExpressionInPatternInlineConstSugg {
     pub end_span: Span,
 }
 
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(
+    parse_unexpected_expr_in_pat_remove_let_sugg,
+    applicability = "maybe-incorrect"
+)]
+pub(crate) struct UnexpectedExpressionInPatternRemoveLetSugg {
+    #[suggestion_part(code = "")]
+    pub span: Span,
+}
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(
+    parse_unexpected_expr_in_pat_replace_let_else_with_if_sugg,
+    applicability = "maybe-incorrect"
+)]
+pub(crate) struct UnexpectedExpressionInPatternReplaceLetElseWithIfSugg {
+    #[suggestion_part(code = "if {init} != {pat}")]
+    pub span: Span,
+    pub init: String,
+    pub pat: String,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_unexpected_paren_in_range_pat)]
 pub(crate) struct UnexpectedParenInRangePat {
diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs
@@ -8,7 +8,9 @@ use crate::errors::{
     TopLevelOrPatternNotAllowed, TopLevelOrPatternNotAllowedSugg, TrailingVertNotAllowed,
     UnexpectedExpressionInPattern, UnexpectedExpressionInPatternArmSugg,
     UnexpectedExpressionInPatternConstSugg, UnexpectedExpressionInPatternInlineConstSugg,
-    UnexpectedLifetimeInPattern, UnexpectedParenInRangePat, UnexpectedParenInRangePatSugg,
+    UnexpectedExpressionInPatternRemoveLetSugg,
+    UnexpectedExpressionInPatternReplaceLetElseWithIfSugg, UnexpectedLifetimeInPattern,
+    UnexpectedParenInRangePat, UnexpectedParenInRangePatSugg,
     UnexpectedVertVertBeforeFunctionParam, UnexpectedVertVertInPattern,
 };
 use crate::parser::expr::{could_be_unclosed_char_literal, DestructuredFloat, LhsExpr};
@@ -26,7 +28,7 @@ use rustc_errors::{Applicability, Diag, PResult, StashKey};
 use rustc_session::errors::ExprParenthesesNeeded;
 use rustc_span::source_map::{respan, Spanned};
 use rustc_span::symbol::{kw, sym, Ident};
-use rustc_span::{ErrorGuaranteed, Span};
+use rustc_span::{BytePos, ErrorGuaranteed, Span};
 use thin_vec::{thin_vec, ThinVec};
 
 #[derive(PartialEq, Copy, Clone)]
@@ -497,15 +499,38 @@ impl<'a> Parser<'a> {
                             err.span.replace(stash_span, expr_span);
 
                             if let StmtKind::Let(local) = &stmt.kind {
-                                // If we have an `ExprInPat`, the user tried to assign a value to another value,
-                                // which doesn't makes much sense.
                                 match &local.kind {
-                                    LocalKind::Decl => {}
-                                    LocalKind::Init(_) => {}
-                                    LocalKind::InitElse(_, _) => {}
+                                    // help: remove this `let`
+                                    LocalKind::Decl | LocalKind::Init(_) => {
+                                        err.subdiagnostic(
+                                            UnexpectedExpressionInPatternRemoveLetSugg {
+                                                // HACK: retrieves `let`'s span
+                                                span: local
+                                                    .span
+                                                    .shrink_to_lo()
+                                                    .with_hi(local.span.lo() + BytePos(3)),
+                                            },
+                                        );
+                                    }
+                                    // help: replace the `let` with an `if`
+                                    LocalKind::InitElse(init, els) => {
+                                        err.subdiagnostic(
+                                            UnexpectedExpressionInPatternReplaceLetElseWithIfSugg {
+                                                span: local.span.shrink_to_lo().until(els.span),
+                                                init: self
+                                                    .parser
+                                                    .span_to_snippet(init.span)
+                                                    .unwrap(),
+                                                pat: self
+                                                    .parser
+                                                    .span_to_snippet(local.pat.span)
+                                                    .unwrap(),
+                                            },
+                                        );
+                                    }
                                 }
                             } else {
-                                // help: use an arm guard `if val == expr`
+                                // help: check the value in an arm guard
                                 if let Some(arm) = &self.arm {
                                     let (ident, ident_span) = match self.field {
                                         Some(field) => (
diff --git a/tests/ui/parser/bad-name.stderr b/tests/ui/parser/bad-name.stderr
@@ -8,7 +8,9 @@ error: expected a pattern, found an expression
   --> $DIR/bad-name.rs:4:7
    |
 LL |   let x.y::<isize>.z foo;
-   |       ^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
+   |   --- ^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
+   |   |
+   |   help: remove this `let`
 
 error: expected one of `(`, `.`, `::`, `:`, `;`, `=`, `?`, `|`, or an operator, found `foo`
   --> $DIR/bad-name.rs:4:22
diff --git a/tests/ui/parser/issues/issue-24197.stderr b/tests/ui/parser/issues/issue-24197.stderr
@@ -2,7 +2,9 @@ error: expected a pattern, found an expression
   --> $DIR/issue-24197.rs:2:9
    |
 LL |     let buf[0] = 0;
-   |         ^^^^^^ arbitrary expressions are not allowed in patterns
+   |     --- ^^^^^^ arbitrary expressions are not allowed in patterns
+   |     |
+   |     help: remove this `let`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/parser/pat-lt-bracket-5.stderr b/tests/ui/parser/pat-lt-bracket-5.stderr
@@ -2,7 +2,9 @@ error: expected a pattern, found an expression
   --> $DIR/pat-lt-bracket-5.rs:2:9
    |
 LL |     let v[0] = v[1];
-   |         ^^^^ arbitrary expressions are not allowed in patterns
+   |     --- ^^^^ arbitrary expressions are not allowed in patterns
+   |     |
+   |     help: remove this `let`
 
 error[E0425]: cannot find value `v` in this scope
   --> $DIR/pat-lt-bracket-5.rs:2:16
diff --git a/tests/ui/parser/pat-lt-bracket-6.stderr b/tests/ui/parser/pat-lt-bracket-6.stderr
@@ -2,7 +2,9 @@ error: expected a pattern, found an expression
   --> $DIR/pat-lt-bracket-6.rs:5:14
    |
 LL |     let Test(&desc[..]) = x;
-   |              ^^^^^^^^^ arbitrary expressions are not allowed in patterns
+   |     ---      ^^^^^^^^^ arbitrary expressions are not allowed in patterns
+   |     |
+   |     help: remove this `let`
 
 error[E0308]: mismatched types
   --> $DIR/pat-lt-bracket-6.rs:10:30
diff --git a/tests/ui/parser/pat-ranges-3.stderr b/tests/ui/parser/pat-ranges-3.stderr
@@ -2,13 +2,17 @@ error: expected a pattern range bound, found an expression
   --> $DIR/pat-ranges-3.rs:4:16
    |
 LL |     let 10 ..= 10 + 3 = 12;
-   |                ^^^^^^ arbitrary expressions are not allowed in patterns
+   |     ---        ^^^^^^ arbitrary expressions are not allowed in patterns
+   |     |
+   |     help: remove this `let`
 
 error: expected a pattern range bound, found an expression
   --> $DIR/pat-ranges-3.rs:7:9
    |
 LL |     let 10 - 3 ..= 10 = 8;
-   |         ^^^^^^ arbitrary expressions are not allowed in patterns
+   |     --- ^^^^^^ arbitrary expressions are not allowed in patterns
+   |     |
+   |     help: remove this `let`
 
 error: aborting due to 2 previous errors
 
diff --git a/tests/ui/parser/recover/recover-pat-exprs.stderr b/tests/ui/parser/recover/recover-pat-exprs.stderr
@@ -554,7 +554,9 @@ error: expected a pattern, found an expression
   --> $DIR/recover-pat-exprs.rs:71:9
    |
 LL |     let 1 + 1 = 2;
-   |         ^^^^^ arbitrary expressions are not allowed in patterns
+   |     --- ^^^^^ arbitrary expressions are not allowed in patterns
+   |     |
+   |     help: remove this `let`
 
 error: expected one of `)`, `,`, `@`, or `|`, found `*`
   --> $DIR/recover-pat-exprs.rs:74:28
diff --git a/tests/ui/parser/recover/recover-pat-lets.rs b/tests/ui/parser/recover/recover-pat-lets.rs
@@ -0,0 +1,7 @@
+fn main() {
+    let x = Some(2);
+
+    let Some(1 + 1) = x else { //~ error: expected a pattern, found an expression
+        return;
+    };
+}
diff --git a/tests/ui/parser/recover/recover-pat-lets.stderr b/tests/ui/parser/recover/recover-pat-lets.stderr
@@ -0,0 +1,11 @@
+error: expected a pattern, found an expression
+  --> $DIR/recover-pat-lets.rs:4:14
+   |
+LL |     let Some(1 + 1) = x else {
+   |     ---------^^^^^-----------
+   |     |        |
+   |     |        arbitrary expressions are not allowed in patterns
+   |     help: use an `if`: `if x != Some(1 + 1)`
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/sized/ensure-overriding-bindings-in-pattern-with-ty-err-doesnt-ice.stderr b/tests/ui/sized/ensure-overriding-bindings-in-pattern-with-ty-err-doesnt-ice.stderr
@@ -2,7 +2,9 @@ error: expected a pattern, found an expression
   --> $DIR/ensure-overriding-bindings-in-pattern-with-ty-err-doesnt-ice.rs:2:31
    |
 LL |     let str::<{fn str() { let str::T>>::as_bytes; }}, T>::as_bytes;
-   |                               ^^^^^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
+   |                           --- ^^^^^^^^^^^^^^^^^^ arbitrary expressions are not allowed in patterns
+   |                           |
+   |                           help: remove this `let`
 
 error[E0412]: cannot find type `T` in this scope
   --> $DIR/ensure-overriding-bindings-in-pattern-with-ty-err-doesnt-ice.rs:2:55

Original file line number	Diff line number	Diff line change
`@@ -2,7 +2,9 @@ error: expected a pattern, found an expression`
`2`	`2`	`--> $DIR/issue-24197.rs:2:9`
`3`	`3`	`\|`
`4`	`4`	`LL \| let buf[0] = 0;`
`5`		`- \| ^^^^^^ arbitrary expressions are not allowed in patterns`
	`5`	`+ \| --- ^^^^^^ arbitrary expressions are not allowed in patterns`
	`6`	`+ \| \|`
	`7`	+ \| help: remove this `let`
`6`	`8`
`7`	`9`	`error: aborting due to 1 previous error`
`8`	`10`