Differentiate method/tymethod by determining 'defaultness'

Currently a method only has defaultness if it is a provided trait
method, but this will change when specialisation is available and may
need to become a concept known to hir.

I opted to go for a 'fewest changes' approach given specialisation is
still under development.

crates/hir/src/code_model.rs

@@ -772,7 +772,14 @@ impl Function {
         hir_ty::diagnostics::validate_body(db, self.id.into(), sink)
     }
 
-    pub fn parent_def(self, db: &dyn HirDatabase) -> Option<MethodOwner> {
+    /// Whether this function declaration has a definition.
+    ///
+    /// This is false in the case of required (not provided) trait methods.
+    pub fn has_body(self, db: &dyn HirDatabase) -> bool {
+        db.function_data(self.id).has_body
+    }
+
+    pub fn method_owner(self, db: &dyn HirDatabase) -> Option<MethodOwner> {
         match self.as_assoc_item(db).map(|assoc| assoc.container(db)) {
             Some(AssocItemContainer::Trait(t)) => Some(t.into()),
             Some(AssocItemContainer::ImplDef(imp)) => {

crates/hir/src/lib.rs

@@ -35,8 +35,8 @@ pub use crate::{
     code_model::{
         Access, Adt, AsAssocItem, AssocItem, AssocItemContainer, Callable, CallableKind, Const,
         Crate, CrateDependency, DefWithBody, Enum, EnumVariant, Field, FieldSource, Function,
-        GenericDef, HasVisibility, ImplDef, Local, MacroDef, Module, ModuleDef, ScopeDef, Static,
-        Struct, Trait, Type, TypeAlias, TypeParam, Union, VariantDef, Visibility,
+        GenericDef, HasVisibility, ImplDef, Local, MacroDef, MethodOwner, Module, ModuleDef,
+        ScopeDef, Static, Struct, Trait, Type, TypeAlias, TypeParam, Union, VariantDef, Visibility,
     },
     has_source::HasSource,
     semantics::{original_range, PathResolution, Semantics, SemanticsScope},

crates/hir_def/src/data.rs

@@ -25,6 +25,7 @@ pub struct FunctionData {
     /// True if the first param is `self`. This is relevant to decide whether this
     /// can be called as a method.
     pub has_self_param: bool,
+    pub has_body: bool,
     pub is_unsafe: bool,
     pub is_varargs: bool,
     pub visibility: RawVisibility,
@@ -42,6 +43,7 @@ impl FunctionData {
             ret_type: func.ret_type.clone(),
             attrs: item_tree.attrs(ModItem::from(loc.id.value).into()).clone(),
             has_self_param: func.has_self_param,
+            has_body: func.has_body,
             is_unsafe: func.is_unsafe,
             is_varargs: func.is_varargs,
             visibility: item_tree[func.visibility].clone(),

crates/hir_def/src/item_tree.rs

@@ -505,6 +505,7 @@ pub struct Function {
     pub visibility: RawVisibilityId,
     pub generic_params: GenericParamsId,
     pub has_self_param: bool,
+    pub has_body: bool,
     pub is_unsafe: bool,
     pub params: Box<[TypeRef]>,
     pub is_varargs: bool,

crates/hir_def/src/item_tree/lower.rs

@@ -330,12 +330,15 @@ impl Ctx {
             ret_type
         };
 
+        let has_body = func.body().is_some();
+
         let ast_id = self.source_ast_id_map.ast_id(func);
         let mut res = Function {
             name,
             visibility,
             generic_params: GenericParamsId::EMPTY,
             has_self_param,
+            has_body,
             is_unsafe: func.unsafe_token().is_some(),
             params: params.into_boxed_slice(),
             is_varargs,

crates/ide/src/doc_links.rs

@@ -13,7 +13,7 @@ use ide_db::{defs::Definition, RootDatabase};
 
 use hir::{
     db::{DefDatabase, HirDatabase},
-    Adt, AsName, AssocItem, Crate, Field, HasAttrs, ItemInNs, ModuleDef,
+    Adt, AsName, AssocItem, Crate, Field, HasAttrs, ItemInNs, MethodOwner, ModuleDef,
 };
 use ide_db::{
     defs::{classify_name, classify_name_ref, Definition},
@@ -117,7 +117,7 @@ fn get_doc_link(db: &RootDatabase, definition: Definition) -> Option<String> {
     let target_def: ModuleDef = match definition {
         Definition::ModuleDef(moddef) => match moddef {
             ModuleDef::Function(f) => {
-                f.parent_def(db).map(|mowner| mowner.into()).unwrap_or_else(|| f.clone().into())
+                f.method_owner(db).map(|mowner| mowner.into()).unwrap_or_else(|| f.clone().into())
             }
             moddef => moddef,
         },
@@ -401,9 +401,18 @@ fn get_symbol_fragment(db: &dyn HirDatabase, field_or_assoc: &FieldOrAssocItem)
     Some(match field_or_assoc {
         FieldOrAssocItem::Field(field) => format!("#structfield.{}", field.name(db)),
         FieldOrAssocItem::AssocItem(assoc) => match assoc {
-            // TODO: Rustdoc sometimes uses tymethod instead of method. This case needs to be investigated.
-            AssocItem::Function(function) => format!("#method.{}", function.name(db)),
-            // TODO: This might be the old method for documenting associated constants, i32::MAX uses a separate page...
+            AssocItem::Function(function) => {
+                let is_trait_method =
+                    matches!(function.method_owner(db), Some(MethodOwner::Trait(..)));
+                // This distinction may get more complicated when specialisation is available.
+                // In particular this decision is made based on whether a method 'has defaultness'.
+                // Currently this is only the case for provided trait methods.
+                if is_trait_method && !function.has_body(db) {
+                    format!("#tymethod.{}", function.name(db))
+                } else {
+                    format!("#method.{}", function.name(db))
+                }
+            }
             AssocItem::Const(constant) => format!("#associatedconstant.{}", constant.name(db)?),
             AssocItem::TypeAlias(ty) => format!("#associatedtype.{}", ty.name(db)),
         },

editors/code/src/commands.ts

@@ -425,7 +425,7 @@ export function openDocs(ctx: Ctx): Cmd {
         const client = ctx.client;
         const editor = vscode.window.activeTextEditor;
         if (!editor || !client) {
-            return
+            return;
         };
 
         const position = editor.selection.active;