Silence resolve errors on missing let in let-chain

Author: estebank

Diff for: compiler/rustc_parse/src/parser/expr.rs

@@ -2478,7 +2478,12 @@ impl<'a> Parser<'a> {
         let mut cond =
             self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL | Restrictions::ALLOW_LET, None)?;
 
-        CondChecker::new(self).visit_expr(&mut cond);
+        let mut checker = CondChecker::new(self);
+        checker.visit_expr(&mut cond);
+        if checker.seen_missing_let {
+            // Avoid unnecessary resolve errors as we know we'll have some.
+            *self.sess.silence_resolve_errors.borrow_mut() = true;
+        }
 
         if let ExprKind::Let(_, _, _, None) = cond.kind {
             // Remove the last feature gating of a `let` expression since it's stable.
@@ -3556,12 +3561,19 @@ struct CondChecker<'a> {
     parser: &'a Parser<'a>,
     forbid_let_reason: Option<ForbiddenLetReason>,
     missing_let: Option<errors::MaybeMissingLet>,
+    seen_missing_let: bool,
     comparison: Option<errors::MaybeComparison>,
 }
 
 impl<'a> CondChecker<'a> {
     fn new(parser: &'a Parser<'a>) -> Self {
-        CondChecker { parser, forbid_let_reason: None, missing_let: None, comparison: None }
+        CondChecker {
+            parser,
+            forbid_let_reason: None,
+            missing_let: None,
+            seen_missing_let: false,
+            comparison: None,
+        }
     }
 }
 
@@ -3613,6 +3625,7 @@ impl MutVisitor for CondChecker<'_> {
                     | ExprKind::Call(_, _)
                     | ExprKind::Array(_) = rhs.kind
                 {
+                    self.seen_missing_let = true;
                     self.missing_let =
                         Some(errors::MaybeMissingLet { span: rhs.span.shrink_to_lo() });
                 }

Diff for: compiler/rustc_resolve/src/late/diagnostics.rs

@@ -435,6 +435,11 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
             code,
         );
 
+        if *self.r.tcx.sess.parse_sess.silence_resolve_errors.borrow() {
+            // Silence redundant resolve errors that will be caused due to mis-parse fallout.
+            err.delay_as_bug();
+        }
+
         self.suggest_at_operator_in_slice_pat_with_range(&mut err, path);
         self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);
 

Diff for: compiler/rustc_session/src/parse.rs

@@ -217,6 +217,9 @@ pub struct ParseSess {
     pub proc_macro_quoted_spans: AppendOnlyVec<Span>,
     /// Used to generate new `AttrId`s. Every `AttrId` is unique.
     pub attr_id_generator: AttrIdGenerator,
+    /// Track parse errors that will cause unnecessary resolve errors.  This is a crude mechanism,
+    /// we should do something that is scope-based, instead of crate-global.
+    pub silence_resolve_errors: Lock<bool>,
 }
 
 impl ParseSess {
@@ -247,6 +250,7 @@ impl ParseSess {
             assume_incomplete_release: false,
             proc_macro_quoted_spans: Default::default(),
             attr_id_generator: AttrIdGenerator::new(),
+            silence_resolve_errors: Default::default(),
         }
     }
 

Diff for: tests/ui/expr/if/bad-if-let-suggestion-2.rs

@@ -0,0 +1,10 @@
+// FIXME(compiler-errors): This really should suggest `let` on the RHS of the
+// `&&` operator, but that's kinda hard to do because of precedence.
+// Instead, for now we just make sure not to suggest `if let let`.
+fn a() {
+    if let x = 1 && i = 2 {}
+    //~^ ERROR expected expression, found `let` statement
+    //~| ERROR mismatched types
+}
+
+fn main() {}

Diff for: tests/ui/expr/if/bad-if-let-suggestion-2.stderr

@@ -0,0 +1,30 @@
+error: expected expression, found `let` statement
+  --> $DIR/bad-if-let-suggestion-2.rs:5:8
+   |
+LL |     if let x = 1 && i = 2 {}
+   |        ^^^^^^^^^
+   |
+   = note: only supported directly in conditions of `if` and `while` expressions
+help: you might have meant to continue the let-chain
+   |
+LL |     if let x = 1 && let i = 2 {}
+   |                     +++
+help: you might have meant to compare for equality
+   |
+LL |     if let x = 1 && i == 2 {}
+   |                        +
+
+error[E0308]: mismatched types
+  --> $DIR/bad-if-let-suggestion-2.rs:5:8
+   |
+LL |     if let x = 1 && i = 2 {}
+   |        ^^^^^^^^^^^^^^^^^^ expected `bool`, found `()`
+   |
+help: you might have meant to compare for equality
+   |
+LL |     if let x = 1 && i == 2 {}
+   |                        +
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

Diff for: tests/ui/expr/if/bad-if-let-suggestion.rs

@@ -1,12 +1,6 @@
 // FIXME(compiler-errors): This really should suggest `let` on the RHS of the
 // `&&` operator, but that's kinda hard to do because of precedence.
 // Instead, for now we just make sure not to suggest `if let let`.
-fn a() {
-    if let x = 1 && i = 2 {}
-    //~^ ERROR cannot find value `i` in this scope
-    //~| ERROR mismatched types
-    //~| ERROR expected expression, found `let` statement
-}
 
 fn b() {
     if (i + j) = i {}

Diff for: tests/ui/expr/if/bad-if-let-suggestion.stderr

@@ -1,73 +1,30 @@
-error: expected expression, found `let` statement
-  --> $DIR/bad-if-let-suggestion.rs:5:8
-   |
-LL |     if let x = 1 && i = 2 {}
-   |        ^^^^^^^^^
-   |
-   = note: only supported directly in conditions of `if` and `while` expressions
-help: you might have meant to continue the let-chain
-   |
-LL |     if let x = 1 && let i = 2 {}
-   |                     +++
-help: you might have meant to compare for equality
-   |
-LL |     if let x = 1 && i == 2 {}
-   |                        +
-
-error[E0425]: cannot find value `i` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:5:21
-   |
-LL |     if let x = 1 && i = 2 {}
-   |                     ^ not found in this scope
-
 error[E0425]: cannot find value `i` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:12:9
+  --> $DIR/bad-if-let-suggestion.rs:6:9
    |
-LL | fn a() {
-   | ------ similarly named function `a` defined here
-...
 LL |     if (i + j) = i {}
-   |         ^ help: a function with a similar name exists: `a`
+   |         ^ not found in this scope
 
 error[E0425]: cannot find value `j` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:12:13
+  --> $DIR/bad-if-let-suggestion.rs:6:13
    |
-LL | fn a() {
-   | ------ similarly named function `a` defined here
-...
 LL |     if (i + j) = i {}
-   |             ^ help: a function with a similar name exists: `a`
+   |             ^ not found in this scope
 
 error[E0425]: cannot find value `i` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:12:18
+  --> $DIR/bad-if-let-suggestion.rs:6:18
    |
-LL | fn a() {
-   | ------ similarly named function `a` defined here
-...
 LL |     if (i + j) = i {}
-   |                  ^ help: a function with a similar name exists: `a`
+   |                  ^ not found in this scope
 
 error[E0425]: cannot find value `x` in this scope
-  --> $DIR/bad-if-let-suggestion.rs:19:8
+  --> $DIR/bad-if-let-suggestion.rs:13:8
    |
-LL | fn a() {
-   | ------ similarly named function `a` defined here
+LL | fn b() {
+   | ------ similarly named function `b` defined here
 ...
 LL |     if x[0] = 1 {}
-   |        ^ help: a function with a similar name exists: `a`
-
-error[E0308]: mismatched types
-  --> $DIR/bad-if-let-suggestion.rs:5:8
-   |
-LL |     if let x = 1 && i = 2 {}
-   |        ^^^^^^^^^^^^^^^^^^ expected `bool`, found `()`
-   |
-help: you might have meant to compare for equality
-   |
-LL |     if let x = 1 && i == 2 {}
-   |                        +
+   |        ^ help: a function with a similar name exists: `b`
 
-error: aborting due to 7 previous errors
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0308, E0425.
-For more information about an error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0425`.