Merge #11863

11863: fix: allow varargs in any param position r=jonas-schievink a=jonas-schievink

Fixes #3578 and aligns us with the Rust reference.

bors r+

Co-authored-by: Jonas Schievink <jonas.schievink@ferrous-systems.com>

Author: bors[bot]

crates/parser/src/grammar/params.rs

@@ -71,13 +71,10 @@ fn list_(p: &mut Parser, flavor: Flavor) {
             m.abandon(p);
             break;
         }
-        let param = param(p, m, flavor);
+        param(p, m, flavor);
         if !p.at(ket) {
             p.expect(T![,]);
         }
-        if let Variadic(true) = param {
-            break;
-        }
     }
 
     if let Some(m) = param_marker {
@@ -90,27 +87,24 @@ fn list_(p: &mut Parser, flavor: Flavor) {
 
 const PARAM_FIRST: TokenSet = patterns::PATTERN_FIRST.union(types::TYPE_FIRST);
 
-struct Variadic(bool);
-
-fn param(p: &mut Parser, m: Marker, flavor: Flavor) -> Variadic {
-    let mut res = Variadic(false);
+fn param(p: &mut Parser, m: Marker, flavor: Flavor) {
     match flavor {
         // test param_list_vararg
-        // extern "C" { fn printf(format: *const i8, ...) -> i32; }
-        Flavor::FnDef | Flavor::FnPointer if p.eat(T![...]) => res = Variadic(true),
+        // extern "C" { fn printf(format: *const i8, ..., _: u8) -> i32; }
+        Flavor::FnDef | Flavor::FnPointer if p.eat(T![...]) => {}
 
         // test fn_def_param
-        // fn foo((x, y): (i32, i32)) {}
+        // fn foo(..., (x, y): (i32, i32)) {}
         Flavor::FnDef => {
             patterns::pattern(p);
-            if variadic_param(p) {
-                res = Variadic(true);
-            } else if p.at(T![:]) {
-                types::ascription(p);
-            } else {
-                // test_err missing_fn_param_type
-                // fn f(x y: i32, z, t: i32) {}
-                p.error("missing type for function parameter");
+            if !variadic_param(p) {
+                if p.at(T![:]) {
+                    types::ascription(p);
+                } else {
+                    // test_err missing_fn_param_type
+                    // fn f(x y: i32, z, t: i32) {}
+                    p.error("missing type for function parameter");
+                }
             }
         }
         // test value_parameters_no_patterns
@@ -127,12 +121,12 @@ fn param(p: &mut Parser, m: Marker, flavor: Flavor) -> Variadic {
         Flavor::FnPointer => {
             if (p.at(IDENT) || p.at(UNDERSCORE)) && p.nth(1) == T![:] && !p.nth_at(1, T![::]) {
                 patterns::pattern_single(p);
-                if variadic_param(p) {
-                    res = Variadic(true);
-                } else if p.at(T![:]) {
-                    types::ascription(p);
-                } else {
-                    p.error("missing type for function parameter");
+                if !variadic_param(p) {
+                    if p.at(T![:]) {
+                        types::ascription(p);
+                    } else {
+                        p.error("missing type for function parameter");
+                    }
                 }
             } else {
                 types::type_(p);
@@ -150,7 +144,6 @@ fn param(p: &mut Parser, m: Marker, flavor: Flavor) -> Variadic {
         }
     }
     m.complete(p, PARAM);
-    res
 }
 
 fn variadic_param(p: &mut Parser) -> bool {

crates/parser/test_data/parser/inline/ok/0123_param_list_vararg.rast

@@ -34,6 +34,18 @@ SOURCE_FILE
           WHITESPACE " "
           PARAM
             DOT3 "..."
+          COMMA ","
+          WHITESPACE " "
+          PARAM
+            WILDCARD_PAT
+              UNDERSCORE "_"
+            COLON ":"
+            WHITESPACE " "
+            PATH_TYPE
+              PATH
+                PATH_SEGMENT
+                  NAME_REF
+                    IDENT "u8"
           R_PAREN ")"
         WHITESPACE " "
         RET_TYPE

crates/parser/test_data/parser/inline/ok/0123_param_list_vararg.rs

@@ -1 +1 @@
-extern "C" { fn printf(format: *const i8, ...) -> i32; }
+extern "C" { fn printf(format: *const i8, ..., _: u8) -> i32; }

crates/parser/test_data/parser/inline/ok/0156_fn_def_param.rast

@@ -6,6 +6,10 @@ SOURCE_FILE
       IDENT "foo"
     PARAM_LIST
       L_PAREN "("
+      PARAM
+        DOT3 "..."
+      COMMA ","
+      WHITESPACE " "
       PARAM
         TUPLE_PAT
           L_PAREN "("

crates/parser/test_data/parser/inline/ok/0156_fn_def_param.rs

@@ -1 +1 @@
-fn foo((x, y): (i32, i32)) {}
+fn foo(..., (x, y): (i32, i32)) {}