Recover from missing param list in function definitions

10 files changed, 65 insertions, 19 deletions

diff --git a/compiler/rustc_parse/messages.ftl b/compiler/rustc_parse/messages.ftl
index e0778f72bfe..6e0d44bd00e 100644
--- a/compiler/rustc_parse/messages.ftl
+++ b/compiler/rustc_parse/messages.ftl
@@ -523,6 +523,9 @@ parse_missing_fn_for_function_definition = missing `fn` for function definition
 parse_missing_fn_for_method_definition = missing `fn` for method definition
     .suggestion = add `fn` here to parse `{$ident}` as a public method
 
+parse_missing_fn_params = missing parameters for function definition
+    .suggestion = add a parameter list
+
 parse_missing_for_in_trait_impl = missing `for` in a trait impl
     .suggestion = add `for` here
 
diff --git a/compiler/rustc_parse/src/errors.rs b/compiler/rustc_parse/src/errors.rs
index aeb4fd0a304..f22d70ec809 100644
--- a/compiler/rustc_parse/src/errors.rs
+++ b/compiler/rustc_parse/src/errors.rs
@@ -1544,6 +1544,14 @@ pub(crate) enum AmbiguousMissingKwForItemSub {
 }
 
 #[derive(Diagnostic)]
+#[diag(parse_missing_fn_params)]
+pub(crate) struct MissingFnParams {
+    #[primary_span]
+    #[suggestion(code = "()", applicability = "machine-applicable", style = "short")]
+    pub span: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(parse_missing_trait_in_trait_impl)]
 pub(crate) struct MissingTraitInTraitImpl {
     #[primary_span]
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 982f601c0d5..d4f7083c397 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -2492,6 +2492,16 @@ impl<'a> Parser<'a> {
     pub(super) fn parse_fn_params(&mut self, req_name: ReqName) -> PResult<'a, ThinVec<Param>> {
         let mut first_param = true;
         // Parse the arguments, starting out with `self` being allowed...
+        if self.token.kind != TokenKind::OpenDelim(Delimiter::Parenthesis)
+        // might be typo'd trait impl, handled elsewhere
+        && !self.token.is_keyword(kw::For)
+        {
+            // recover from missing argument list, e.g. `fn main -> () {}`
+            self.sess
+                .emit_err(errors::MissingFnParams { span: self.prev_token.span.shrink_to_hi() });
+            return Ok(ThinVec::new());
+        }
+
         let (mut params, _) = self.parse_paren_comma_seq(|p| {
             p.recover_diff_marker();
             let param = p.parse_param_general(req_name, first_param).or_else(|mut e| {
diff --git a/tests/ui/mismatched_types/recovered-block.rs b/tests/ui/mismatched_types/recovered-block.rs
index b230b47d35d..a91bbe7083b 100644
--- a/tests/ui/mismatched_types/recovered-block.rs
+++ b/tests/ui/mismatched_types/recovered-block.rs
@@ -12,10 +12,4 @@ pub fn foo() -> Foo {
 }
 //~^^ ERROR missing `struct` for struct definition
 
-pub fn bar() -> Foo {
-    fn
-    Foo { text: "".to_string() }
-}
-//~^^ ERROR expected one of `(` or `<`, found `{`
-
 fn main() {}
diff --git a/tests/ui/mismatched_types/recovered-block.stderr b/tests/ui/mismatched_types/recovered-block.stderr
index f275321abe5..88d62545656 100644
--- a/tests/ui/mismatched_types/recovered-block.stderr
+++ b/tests/ui/mismatched_types/recovered-block.stderr
@@ -9,11 +9,5 @@ help: add `struct` here to parse `Foo` as a public struct
 LL |     pub struct Foo { text }
    |         ++++++
 
-error: expected one of `(` or `<`, found `{`
-  --> $DIR/recovered-block.rs:17:9
-   |
-LL |     Foo { text: "".to_string() }
-   |         ^ expected one of `(` or `<`
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
diff --git a/tests/ui/parser/issues/issue-108109-fn-missing-params.fixed b/tests/ui/parser/issues/issue-108109-fn-missing-params.fixed
new file mode 100644
index 00000000000..b819aa810cb
--- /dev/null
+++ b/tests/ui/parser/issues/issue-108109-fn-missing-params.fixed
@@ -0,0 +1,9 @@
+// run-rustfix
+
+pub fn missing() -> () {}
+//~^ ERROR missing parameters for function definition
+
+pub fn missing2() {}
+//~^ ERROR missing parameters for function definition
+
+fn main() {}
diff --git a/tests/ui/parser/issues/issue-108109-fn-missing-params.rs b/tests/ui/parser/issues/issue-108109-fn-missing-params.rs
new file mode 100644
index 00000000000..01efe728081
--- /dev/null
+++ b/tests/ui/parser/issues/issue-108109-fn-missing-params.rs
@@ -0,0 +1,9 @@
+// run-rustfix
+
+pub fn missing -> () {}
+//~^ ERROR missing parameters for function definition
+
+pub fn missing2 {}
+//~^ ERROR missing parameters for function definition
+
+fn main() {}
diff --git a/tests/ui/parser/issues/issue-108109-fn-missing-params.stderr b/tests/ui/parser/issues/issue-108109-fn-missing-params.stderr
new file mode 100644
index 00000000000..86d3449cc33
--- /dev/null
+++ b/tests/ui/parser/issues/issue-108109-fn-missing-params.stderr
@@ -0,0 +1,14 @@
+error: missing parameters for function definition
+  --> $DIR/issue-108109-fn-missing-params.rs:3:15
+   |
+LL | pub fn missing -> () {}
+   |               ^ help: add a parameter list
+
+error: missing parameters for function definition
+  --> $DIR/issue-108109-fn-missing-params.rs:6:16
+   |
+LL | pub fn missing2 {}
+   |                ^ help: add a parameter list
+
+error: aborting due to 2 previous errors
+
diff --git a/tests/ui/parser/removed-syntax-fn-sigil.rs b/tests/ui/parser/removed-syntax-fn-sigil.rs
index 725843429c0..d55a032d1f2 100644
--- a/tests/ui/parser/removed-syntax-fn-sigil.rs
+++ b/tests/ui/parser/removed-syntax-fn-sigil.rs
@@ -1,3 +1,4 @@
 fn main() {
-    let x: fn~() = || (); //~ ERROR expected `(`, found `~`
+    let x: fn~() = || (); //~ ERROR missing parameters for function definition
+    //~| ERROR expected one of `->`, `;`, or `=`, found `~`
 }
diff --git a/tests/ui/parser/removed-syntax-fn-sigil.stderr b/tests/ui/parser/removed-syntax-fn-sigil.stderr
index 196a5af4729..0d377416700 100644
--- a/tests/ui/parser/removed-syntax-fn-sigil.stderr
+++ b/tests/ui/parser/removed-syntax-fn-sigil.stderr
@@ -1,10 +1,14 @@
-error: expected `(`, found `~`
+error: missing parameters for function definition
   --> $DIR/removed-syntax-fn-sigil.rs:2:14
    |
 LL |     let x: fn~() = || ();
-   |         -    ^ expected `(`
-   |         |
-   |         while parsing the type for `x`
+   |              ^ help: add a parameter list
 
-error: aborting due to previous error
+error: expected one of `->`, `;`, or `=`, found `~`
+  --> $DIR/removed-syntax-fn-sigil.rs:2:14
+   |
+LL |     let x: fn~() = || ();
+   |              ^ expected one of `->`, `;`, or `=`
+
+error: aborting due to 2 previous errors