Fix incorrect handling of cfg'd varargs

crates/hir-def/src/data.rs

@@ -73,6 +73,17 @@ impl FunctionData {
                 flags.remove(FnFlags::HAS_SELF_PARAM);
             }
         }
+        if flags.contains(FnFlags::IS_VARARGS) {
+            if let Some((_, param)) = func.params.iter().enumerate().rev().find(|&(idx, _)| {
+                item_tree.attrs(db, krate, attr_owner(idx)).is_cfg_enabled(cfg_options)
+            }) {
+                if param.type_ref.is_some() {
+                    flags.remove(FnFlags::IS_VARARGS);
+                }
+            } else {
+                flags.remove(FnFlags::IS_VARARGS);
+            }
+        }
 
         let attrs = item_tree.attrs(db, krate, ModItem::from(loc.id.value).into());
         let legacy_const_generics_indices = attrs
@@ -92,7 +103,7 @@ impl FunctionData {
                 .filter(|&(idx, _)| {
                     item_tree.attrs(db, krate, attr_owner(idx)).is_cfg_enabled(cfg_options)
                 })
-                .map(|(_, param)| param.type_ref.clone())
+                .filter_map(|(_, param)| param.type_ref.clone())
                 .collect(),
             ret_type: func.ret_type.clone(),
             attrs: item_tree.attrs(db, krate, ModItem::from(loc.id.value).into()),

crates/hir-def/src/item_tree.rs

@@ -741,7 +741,7 @@ pub struct Function {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Param {
-    pub type_ref: Interned<TypeRef>,
+    pub type_ref: Option<Interned<TypeRef>>,
 }
 
 bitflags::bitflags! {

crates/hir-def/src/item_tree/lower.rs

@@ -380,7 +380,7 @@ impl<'a> Ctx<'a> {
                     }
                 };
                 let type_ref = Interned::new(self_type);
-                params.push(Param { type_ref });
+                params.push(Param { type_ref: Some(type_ref) });
                 has_self_param = true;
             }
             for param in param_list.params() {
@@ -388,12 +388,12 @@ impl<'a> Ctx<'a> {
                 let param = match param.dotdotdot_token() {
                     Some(_) => {
                         has_var_args = true;
-                        Param { type_ref: Interned::new(TypeRef::Error) }
+                        Param { type_ref: None }
                     }
                     None => {
                         let type_ref = TypeRef::from_ast_opt(&self.body_ctx, param.ty());
                         let ty = Interned::new(type_ref);
-                        Param { type_ref: ty }
+                        Param { type_ref: Some(ty) }
                     }
                 };
                 params.push(param);

crates/hir-def/src/item_tree/pretty.rs

@@ -291,7 +291,7 @@ impl Printer<'_> {
                             if idx == 0 && flags.contains(FnFlags::HAS_SELF_PARAM) {
                                 w!(this, "self: ");
                             }
-                            if idx != params.len() {
+                            if let Some(type_ref) = type_ref {
                                 this.print_type_ref(type_ref);
                             } else {
                                 wln!(this, "...");

crates/hir-ty/src/infer.rs

@@ -812,9 +812,7 @@ impl<'a> InferenceContext<'a> {
                 None => self.err_ty(),
             };
 
-            if let Some(ty) = param_tys.last_mut() {
-                *ty = va_list_ty;
-            }
+            param_tys.push(va_list_ty);
         }
         let mut param_tys = param_tys.into_iter().chain(iter::repeat(self.table.new_type_var()));
         if let Some(self_param) = self.body.self_param {

crates/hir-ty/src/tests/patterns.rs

@@ -1126,6 +1126,23 @@ fn var_args() {
 pub struct VaListImpl<'f>;
 fn my_fn(foo: ...) {}
        //^^^ VaListImpl<'?>
+fn my_fn2(bar: u32, foo: ...) {}
+                  //^^^ VaListImpl<'?>
+"#,
+    );
+}
+
+#[test]
+fn var_args_cond() {
+    check_types(
+        r#"
+#[lang = "va_list"]
+pub struct VaListImpl<'f>;
+fn my_fn(bar: u32, #[cfg(FALSE)] foo: ..., #[cfg(not(FALSE))] foo: u32) {
+    foo;
+  //^^^ u32
+
+}
 "#,
     );
 }

crates/hir/src/display.rs

@@ -99,13 +99,7 @@ impl HirDisplay for Function {
         }
 
         // FIXME: Use resolved `param.ty` once we no longer discard lifetimes
-        for (type_ref, param) in data
-            .params
-            .iter()
-            .zip(self.assoc_fn_params(db))
-            .take(data.params.len() - data.is_varargs() as usize)
-            .skip(skip_self)
-        {
+        for (type_ref, param) in data.params.iter().zip(self.assoc_fn_params(db)).skip(skip_self) {
             let local = param.as_local(db).map(|it| it.name(db));
             if !first {
                 f.write_str(", ")?;

crates/intern/src/symbol/symbols.rs

@@ -56,6 +56,7 @@ macro_rules! define_symbols {
 define_symbols! {
     @WITH_NAME:
 
+    dotdotdot = "...",
     INTEGER_0 = "0",
     INTEGER_1 = "1",
     INTEGER_2 = "2",