Rollup merge of #117212 - clubby789:fix-ternary-recover, r=compiler-errors

Properly restore snapshot when failing to recover parsing ternary

If the recovery parsed an expression, then failed to eat a `:`, it would return `false` without restoring the snapshot. Fix this by always restoring the snapshot when returning `false`.

Draft for now because I'd like to try and improve this recovery further.

Fixes #117208

3 files changed, 35 insertions, 141 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 9f8361a4b1e..7b5bb319ed8 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -504,8 +504,10 @@ impl<'a> Parser<'a> {
 
         // Special-case "expected `;`" errors
         if expected.contains(&TokenType::Token(token::Semi)) {
-            if self.prev_token == token::Question && self.maybe_recover_from_ternary_operator() {
-                return Ok(true);
+            // If the user is trying to write a ternary expression, recover it and
+            // return an Err to prevent a cascade of irrelevant diagnostics
+            if self.prev_token == token::Question && let Err(e) = self.maybe_recover_from_ternary_operator() {
+                return Err(e);
             }
 
             if self.token.span == DUMMY_SP || self.prev_token.span == DUMMY_SP {
@@ -1428,10 +1430,10 @@ impl<'a> Parser<'a> {
 
     /// Rust has no ternary operator (`cond ? then : else`). Parse it and try
     /// to recover from it if `then` and `else` are valid expressions. Returns
-    /// whether it was a ternary operator.
-    pub(super) fn maybe_recover_from_ternary_operator(&mut self) -> bool {
+    /// an err if this appears to be a ternary expression.
+    pub(super) fn maybe_recover_from_ternary_operator(&mut self) -> PResult<'a, ()> {
         if self.prev_token != token::Question {
-            return false;
+            return PResult::Ok(());
         }
 
         let lo = self.prev_token.span.lo();
@@ -1449,20 +1451,18 @@ impl<'a> Parser<'a> {
             if self.eat_noexpect(&token::Colon) {
                 match self.parse_expr() {
                     Ok(_) => {
-                        self.sess.emit_err(TernaryOperator { span: self.token.span.with_lo(lo) });
-                        return true;
+                        return Err(self
+                            .sess
+                            .create_err(TernaryOperator { span: self.token.span.with_lo(lo) }));
                     }
                     Err(err) => {
                         err.cancel();
-                        self.restore_snapshot(snapshot);
                     }
                 };
             }
-        } else {
-            self.restore_snapshot(snapshot);
-        };
-
-        false
+        }
+        self.restore_snapshot(snapshot);
+        Ok(())
     }
 
     pub(super) fn maybe_recover_from_bad_type_plus(&mut self, ty: &Ty) -> PResult<'a, ()> {
diff --git a/tests/ui/parser/ternary_operator.rs b/tests/ui/parser/ternary_operator.rs
index 23d537e77f7..c8810781b3d 100644
--- a/tests/ui/parser/ternary_operator.rs
+++ b/tests/ui/parser/ternary_operator.rs
@@ -1,69 +1,30 @@
-// A good chunk of these errors aren't shown to the user, but are still
-// required in the test for it to pass.
-
-fn a() { //~ NOTE this function should return `Result` or `Option` to accept `?`
+fn a() {
     let x = 5 > 2 ? true : false;
     //~^ ERROR Rust has no ternary operator
     //~| HELP use an `if-else` expression instead
-    //~| ERROR the `?` operator can only be applied to values that implement `Try` [E0277]
-    //~| HELP the trait `Try` is not implemented for `{integer}`
-    //~| ERROR the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`) [E0277]
-    //~| HELP the trait `FromResidual<_>` is not implemented for `()`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE the `?` operator cannot be applied to type `{integer}`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE cannot use the `?` operator in a function that returns `()`
-    //~| NOTE in this expansion of desugaring of operator `?`
 }
 
-fn b() { //~ NOTE this function should return `Result` or `Option` to accept `?`
+fn b() {
     let x = 5 > 2 ? { true } : { false };
     //~^ ERROR Rust has no ternary operator
     //~| HELP use an `if-else` expression instead
-    //~| ERROR the `?` operator can only be applied to values that implement `Try` [E0277]
-    //~| HELP the trait `Try` is not implemented for `{integer}`
-    //~| ERROR the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`) [E0277]
-    //~| HELP the trait `FromResidual<_>` is not implemented for `()`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE the `?` operator cannot be applied to type `{integer}`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE cannot use the `?` operator in a function that returns `()`
-    //~| NOTE in this expansion of desugaring of operator `?`
 }
 
-fn c() { //~ NOTE this function should return `Result` or `Option` to accept `?`
+fn c() {
     let x = 5 > 2 ? f32::MAX : f32::MIN;
     //~^ ERROR Rust has no ternary operator
     //~| HELP use an `if-else` expression instead
-    //~| ERROR the `?` operator can only be applied to values that implement `Try` [E0277]
-    //~| HELP the trait `Try` is not implemented for `{integer}`
-    //~| ERROR the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`) [E0277]
-    //~| HELP the trait `FromResidual<_>` is not implemented for `()`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE the `?` operator cannot be applied to type `{integer}`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE cannot use the `?` operator in a function that returns `()`
-    //~| NOTE in this expansion of desugaring of operator `?`
 }
 
-fn main() { //~ NOTE this function should return `Result` or `Option` to accept `?`
+fn bad() {
+    // regression test for #117208
+    v ? return;
+    //~^ ERROR expected one of
+}
+
+fn main() {
     let x = 5 > 2 ? { let x = vec![]: Vec<u16>; x } : { false };
     //~^ ERROR Rust has no ternary operator
     //~| HELP use an `if-else` expression instead
     //~| ERROR expected one of `.`, `;`, `?`, `else`, or an operator, found `:`
-    //~| NOTE expected one of `.`, `;`, `?`, `else`, or an operator
-    //~| ERROR the `?` operator can only be applied to values that implement `Try` [E0277]
-    //~| HELP the trait `Try` is not implemented for `{integer}`
-    //~| ERROR the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`) [E0277]
-    //~| HELP the trait `FromResidual<_>` is not implemented for `()`
-    //~| NOTE type ascription syntax has been removed, see issue #101728 <https://github.com/rust-lang/rust/issues/101728>
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE the `?` operator cannot be applied to type `{integer}`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE in this expansion of desugaring of operator `?`
-    //~| NOTE cannot use the `?` operator in a function that returns `()`
-    //~| NOTE in this expansion of desugaring of operator `?`
 }
diff --git a/tests/ui/parser/ternary_operator.stderr b/tests/ui/parser/ternary_operator.stderr
index af9565bbead..6635e1672f7 100644
--- a/tests/ui/parser/ternary_operator.stderr
+++ b/tests/ui/parser/ternary_operator.stderr
@@ -1,5 +1,5 @@
 error: Rust has no ternary operator
-  --> $DIR/ternary_operator.rs:5:19
+  --> $DIR/ternary_operator.rs:2:19
    |
 LL |     let x = 5 > 2 ? true : false;
    |                   ^^^^^^^^^^^^^^^
@@ -7,7 +7,7 @@ LL |     let x = 5 > 2 ? true : false;
    = help: use an `if-else` expression instead
 
 error: Rust has no ternary operator
-  --> $DIR/ternary_operator.rs:21:19
+  --> $DIR/ternary_operator.rs:8:19
    |
 LL |     let x = 5 > 2 ? { true } : { false };
    |                   ^^^^^^^^^^^^^^^^^^^^^^^
@@ -15,15 +15,21 @@ LL |     let x = 5 > 2 ? { true } : { false };
    = help: use an `if-else` expression instead
 
 error: Rust has no ternary operator
-  --> $DIR/ternary_operator.rs:37:19
+  --> $DIR/ternary_operator.rs:14:19
    |
 LL |     let x = 5 > 2 ? f32::MAX : f32::MIN;
    |                   ^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: use an `if-else` expression instead
 
+error: expected one of `.`, `;`, `?`, `}`, or an operator, found keyword `return`
+  --> $DIR/ternary_operator.rs:21:9
+   |
+LL |     v ? return;
+   |         ^^^^^^ expected one of `.`, `;`, `?`, `}`, or an operator
+
 error: expected one of `.`, `;`, `?`, `else`, or an operator, found `:`
-  --> $DIR/ternary_operator.rs:53:37
+  --> $DIR/ternary_operator.rs:26:37
    |
 LL |     let x = 5 > 2 ? { let x = vec![]: Vec<u16>; x } : { false };
    |                                     ^ expected one of `.`, `;`, `?`, `else`, or an operator
@@ -31,85 +37,12 @@ LL |     let x = 5 > 2 ? { let x = vec![]: Vec<u16>; x } : { false };
    = note: type ascription syntax has been removed, see issue #101728 <https://github.com/rust-lang/rust/issues/101728>
 
 error: Rust has no ternary operator
-  --> $DIR/ternary_operator.rs:53:19
+  --> $DIR/ternary_operator.rs:26:19
    |
 LL |     let x = 5 > 2 ? { let x = vec![]: Vec<u16>; x } : { false };
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: use an `if-else` expression instead
 
-error[E0277]: the `?` operator can only be applied to values that implement `Try`
-  --> $DIR/ternary_operator.rs:5:17
-   |
-LL |     let x = 5 > 2 ? true : false;
-   |                 ^^^ the `?` operator cannot be applied to type `{integer}`
-   |
-   = help: the trait `Try` is not implemented for `{integer}`
-
-error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
-  --> $DIR/ternary_operator.rs:5:19
-   |
-LL | fn a() {
-   | ------ this function should return `Result` or `Option` to accept `?`
-LL |     let x = 5 > 2 ? true : false;
-   |                   ^ cannot use the `?` operator in a function that returns `()`
-   |
-   = help: the trait `FromResidual<_>` is not implemented for `()`
-
-error[E0277]: the `?` operator can only be applied to values that implement `Try`
-  --> $DIR/ternary_operator.rs:21:17
-   |
-LL |     let x = 5 > 2 ? { true } : { false };
-   |                 ^^^ the `?` operator cannot be applied to type `{integer}`
-   |
-   = help: the trait `Try` is not implemented for `{integer}`
-
-error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
-  --> $DIR/ternary_operator.rs:21:19
-   |
-LL | fn b() {
-   | ------ this function should return `Result` or `Option` to accept `?`
-LL |     let x = 5 > 2 ? { true } : { false };
-   |                   ^ cannot use the `?` operator in a function that returns `()`
-   |
-   = help: the trait `FromResidual<_>` is not implemented for `()`
-
-error[E0277]: the `?` operator can only be applied to values that implement `Try`
-  --> $DIR/ternary_operator.rs:37:17
-   |
-LL |     let x = 5 > 2 ? f32::MAX : f32::MIN;
-   |                 ^^^ the `?` operator cannot be applied to type `{integer}`
-   |
-   = help: the trait `Try` is not implemented for `{integer}`
-
-error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
-  --> $DIR/ternary_operator.rs:37:19
-   |
-LL | fn c() {
-   | ------ this function should return `Result` or `Option` to accept `?`
-LL |     let x = 5 > 2 ? f32::MAX : f32::MIN;
-   |                   ^ cannot use the `?` operator in a function that returns `()`
-   |
-   = help: the trait `FromResidual<_>` is not implemented for `()`
-
-error[E0277]: the `?` operator can only be applied to values that implement `Try`
-  --> $DIR/ternary_operator.rs:53:17
-   |
-LL |     let x = 5 > 2 ? { let x = vec![]: Vec<u16>; x } : { false };
-   |                 ^^^ the `?` operator cannot be applied to type `{integer}`
-   |
-   = help: the trait `Try` is not implemented for `{integer}`
-
-error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
-  --> $DIR/ternary_operator.rs:53:19
-   |
-LL | fn main() {
-   | --------- this function should return `Result` or `Option` to accept `?`
-LL |     let x = 5 > 2 ? { let x = vec![]: Vec<u16>; x } : { false };
-   |                   ^ cannot use the `?` operator in a function that returns `()`
-   |
-   = help: the trait `FromResidual<_>` is not implemented for `()`
-
-error: aborting due to 13 previous errors
+error: aborting due to 6 previous errors
 
-For more information about this error, try `rustc --explain E0277`.