Next gen IDs for functions

The current system with AstIds has two primaraly drawbacks:

* It is possible to manufacture IDs out of thin air.
  For example, it's possible to create IDs for items which are not
  considered in CrateDefMap due to cfg. Or it is possible to mixup
  structs and unions, because they share ID space.

* Getting the ID of a parent requires a secondary index.

Instead, the plan is to pursue the more traditional approach, where
each items stores the id of the parent declaration. This makes
`FromSource` more awkward, but also more correct: now, to get from an
AST to HIR, we first do this recursively for the parent item, and the
just search the children of the parent for the matching def

crates/ra_hir/src/code_model.rs

@@ -12,7 +12,8 @@ use hir_def::{
     builtin_type::BuiltinType,
     traits::TraitData,
     type_ref::{Mutability, TypeRef},
-    AssocItemId, CrateModuleId, ImplId, LocalEnumVariantId, LocalStructFieldId, ModuleId, UnionId,
+    AssocItemId, CrateModuleId, FunctionContainerId, HasModule, ImplId, LocalEnumVariantId,
+    LocalStructFieldId, Lookup, ModuleId, UnionId,
 };
 use hir_expand::{
     diagnostics::DiagnosticSink,
@@ -647,7 +648,7 @@ impl FnData {
 
 impl Function {
     pub fn module(self, db: &impl DefDatabase) -> Module {
-        Module { id: self.id.module(db) }
+        self.id.lookup(db).module(db).into()
     }
 
     pub fn krate(self, db: &impl DefDatabase) -> Option<Crate> {
@@ -680,21 +681,25 @@ impl Function {
 
     /// The containing impl block, if this is a method.
     pub fn impl_block(self, db: &impl DefDatabase) -> Option<ImplBlock> {
-        ImplBlock::containing(db, self.into())
+        match self.container(db) {
+            Some(Container::ImplBlock(it)) => Some(it),
+            _ => None,
+        }
     }
 
     /// The containing trait, if this is a trait method definition.
     pub fn parent_trait(self, db: &impl DefDatabase) -> Option<Trait> {
-        db.trait_items_index(self.module(db).id).get_parent_trait(self.id.into()).map(Trait::from)
+        match self.container(db) {
+            Some(Container::Trait(it)) => Some(it),
+            _ => None,
+        }
     }
 
     pub fn container(self, db: &impl DefDatabase) -> Option<Container> {
-        if let Some(impl_block) = self.impl_block(db) {
-            Some(impl_block.into())
-        } else if let Some(trait_) = self.parent_trait(db) {
-            Some(trait_.into())
-        } else {
-            None
+        match self.id.lookup(db).container {
+            FunctionContainerId::TraitId(it) => Some(Container::Trait(it.into())),
+            FunctionContainerId::ImplId(it) => Some(Container::ImplBlock(it.into())),
+            FunctionContainerId::ModuleId(_) => None,
         }
     }
 

crates/ra_hir/src/code_model/src.rs

@@ -1,5 +1,6 @@
 //! FIXME: write short doc here
 
+use hir_def::{HasSource as _, Lookup};
 use ra_syntax::ast::{self, AstNode};
 
 use crate::{
@@ -113,7 +114,7 @@ impl HasSource for EnumVariant {
 impl HasSource for Function {
     type Ast = ast::FnDef;
     fn source(self, db: &(impl DefDatabase + AstDatabase)) -> Source<ast::FnDef> {
-        self.id.source(db)
+        self.id.lookup(db).source(db)
     }
 }
 impl HasSource for Const {

crates/ra_hir/src/from_source.rs

@@ -4,15 +4,15 @@ use hir_def::{ModuleId, StructId, StructOrUnionId, UnionId};
 use hir_expand::{name::AsName, AstId, MacroDefId, MacroDefKind};
 use ra_syntax::{
     ast::{self, AstNode, NameOwner},
-    match_ast,
+    match_ast, AstPtr,
 };
 
 use crate::{
     db::{AstDatabase, DefDatabase, HirDatabase},
     ids::{AstItemDef, LocationCtx},
-    Const, DefWithBody, Enum, EnumVariant, FieldSource, Function, HasBody, HasSource, ImplBlock,
-    Local, MacroDef, Module, ModuleSource, Source, Static, Struct, StructField, Trait, TypeAlias,
-    Union, VariantDef,
+    AssocItem, Const, DefWithBody, Enum, EnumVariant, FieldSource, Function, HasBody, HasSource,
+    ImplBlock, Local, MacroDef, Module, ModuleDef, ModuleSource, Source, Static, Struct,
+    StructField, Trait, TypeAlias, Union, VariantDef,
 };
 
 pub trait FromSource: Sized {
@@ -52,10 +52,51 @@ impl FromSource for Trait {
 impl FromSource for Function {
     type Ast = ast::FnDef;
     fn from_source(db: &(impl DefDatabase + AstDatabase), src: Source<Self::Ast>) -> Option<Self> {
-        let id = from_source(db, src)?;
-        Some(Function { id })
+        // FIXME: this doesn't try to handle nested declarations
+        for container in src.value.syntax().ancestors() {
+            let res = match_ast! {
+                match container {
+                    ast::TraitDef(it) => {
+                        let c = Trait::from_source(db, src.with_value(it))?;
+                        c.items(db)
+                            .into_iter()
+                            .filter_map(|it| match it {
+                                AssocItem::Function(it) => Some(it),
+                                _ => None
+                            })
+                            .find(|it| same_source(&it.source(db), &src))?
+                    },
+                    ast::ImplBlock(it) => {
+                        let c = ImplBlock::from_source(db, src.with_value(it))?;
+                        c.items(db)
+                            .into_iter()
+                            .filter_map(|it| match it {
+                                AssocItem::Function(it) => Some(it),
+                                _ => None
+                            })
+                            .find(|it| same_source(&it.source(db), &src))?
+
+                     },
+                    _ => { continue },
+                }
+            };
+            return Some(res);
+        }
+
+        let module_source = ModuleSource::from_child_node(db, src.as_ref().map(|it| it.syntax()));
+        let c = Module::from_definition(db, src.with_value(module_source))?;
+        let res = c
+            .declarations(db)
+            .into_iter()
+            .filter_map(|it| match it {
+                ModuleDef::Function(it) => Some(it),
+                _ => None,
+            })
+            .find(|it| same_source(&it.source(db), &src));
+        res
     }
 }
+
 impl FromSource for Const {
     type Ast = ast::ConstDef;
     fn from_source(db: &(impl DefDatabase + AstDatabase), src: Source<Self::Ast>) -> Option<Self> {
@@ -108,7 +149,7 @@ impl FromSource for EnumVariant {
         let parent_enum = src.value.parent_enum();
         let src_enum = Source { file_id: src.file_id, value: parent_enum };
         let variants = Enum::from_source(db, src_enum)?.variants(db);
-        variants.into_iter().find(|v| v.source(db) == src)
+        variants.into_iter().find(|v| same_source(&v.source(db), &src))
     }
 }
 
@@ -216,3 +257,13 @@ where
     let ctx = LocationCtx::new(db, module.id, src.file_id);
     Some(DEF::from_ast(ctx, &src.value))
 }
+
+/// XXX: AST Nodes and SyntaxNodes have identity equality semantics: nodes are
+/// equal if they point to exactly the same object.
+///
+/// In general, we do not guarantee that we have exactly one instance of a
+/// syntax tree for each file. We probably should add such guanratree, but, for
+/// the time being, we will use identity-less AstPtr comparison.
+fn same_source<N: AstNode>(s1: &Source<N>, s2: &Source<N>) -> bool {
+    s1.as_ref().map(AstPtr::new) == s2.as_ref().map(AstPtr::new)
+}

crates/ra_hir/src/source_binder.rs

@@ -70,7 +70,7 @@ fn def_with_body_from_child_node(
     child.value.ancestors().find_map(|node| {
         match_ast! {
             match node {
-                ast::FnDef(def)  => { Some(Function {id: ctx.to_def(&def) }.into()) },
+                ast::FnDef(def)  => { return Function::from_source(db, child.with_value(def)).map(DefWithBody::from); },
                 ast::ConstDef(def) => { Some(Const { id: ctx.to_def(&def) }.into()) },
                 ast::StaticDef(def) => { Some(Static { id: ctx.to_def(&def) }.into()) },
                 _ => { None },