1 files changed, 135 insertions, 0 deletions

diff --git a/crates/hir/src/has_source.rs b/crates/hir/src/has_source.rs
new file mode 100644
index 000000000..a50d4ff02
--- /dev/null
+++ b/crates/hir/src/has_source.rs
@@ -0,0 +1,135 @@
+//! FIXME: write short doc here
+
+use either::Either;
+use hir_def::{
+    nameres::{ModuleOrigin, ModuleSource},
+    src::{HasChildSource, HasSource as _},
+    Lookup, VariantId,
+};
+use syntax::ast;
+
+use crate::{
+    db::HirDatabase, Const, Enum, EnumVariant, Field, FieldSource, Function, ImplDef, MacroDef,
+    Module, Static, Struct, Trait, TypeAlias, TypeParam, Union,
+};
+
+pub use hir_expand::InFile;
+
+pub trait HasSource {
+    type Ast;
+    fn source(self, db: &dyn HirDatabase) -> InFile<Self::Ast>;
+}
+
+/// NB: Module is !HasSource, because it has two source nodes at the same time:
+/// definition and declaration.
+impl Module {
+    /// Returns a node which defines this module. That is, a file or a `mod foo {}` with items.
+    pub fn definition_source(self, db: &dyn HirDatabase) -> InFile<ModuleSource> {
+        let def_map = db.crate_def_map(self.id.krate);
+        def_map[self.id.local_id].definition_source(db.upcast())
+    }
+
+    pub fn is_mod_rs(self, db: &dyn HirDatabase) -> bool {
+        let def_map = db.crate_def_map(self.id.krate);
+        match def_map[self.id.local_id].origin {
+            ModuleOrigin::File { is_mod_rs, .. } => is_mod_rs,
+            _ => false,
+        }
+    }
+
+    /// Returns a node which declares this module, either a `mod foo;` or a `mod foo {}`.
+    /// `None` for the crate root.
+    pub fn declaration_source(self, db: &dyn HirDatabase) -> Option<InFile<ast::Module>> {
+        let def_map = db.crate_def_map(self.id.krate);
+        def_map[self.id.local_id].declaration_source(db.upcast())
+    }
+}
+
+impl HasSource for Field {
+    type Ast = FieldSource;
+    fn source(self, db: &dyn HirDatabase) -> InFile<FieldSource> {
+        let var = VariantId::from(self.parent);
+        let src = var.child_source(db.upcast());
+        src.map(|it| match it[self.id].clone() {
+            Either::Left(it) => FieldSource::Pos(it),
+            Either::Right(it) => FieldSource::Named(it),
+        })
+    }
+}
+impl HasSource for Struct {
+    type Ast = ast::Struct;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Struct> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Union {
+    type Ast = ast::Union;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Union> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Enum {
+    type Ast = ast::Enum;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Enum> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for EnumVariant {
+    type Ast = ast::Variant;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Variant> {
+        self.parent.id.child_source(db.upcast()).map(|map| map[self.id].clone())
+    }
+}
+impl HasSource for Function {
+    type Ast = ast::Fn;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Fn> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Const {
+    type Ast = ast::Const;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Const> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Static {
+    type Ast = ast::Static;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Static> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for Trait {
+    type Ast = ast::Trait;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Trait> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for TypeAlias {
+    type Ast = ast::TypeAlias;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::TypeAlias> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+impl HasSource for MacroDef {
+    type Ast = ast::MacroCall;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::MacroCall> {
+        InFile {
+            file_id: self.id.ast_id.expect("MacroDef without ast_id").file_id,
+            value: self.id.ast_id.expect("MacroDef without ast_id").to_node(db.upcast()),
+        }
+    }
+}
+impl HasSource for ImplDef {
+    type Ast = ast::Impl;
+    fn source(self, db: &dyn HirDatabase) -> InFile<ast::Impl> {
+        self.id.lookup(db.upcast()).source(db.upcast())
+    }
+}
+
+impl HasSource for TypeParam {
+    type Ast = Either<ast::Trait, ast::TypeParam>;
+    fn source(self, db: &dyn HirDatabase) -> InFile<Self::Ast> {
+        let child_source = self.id.parent.child_source(db.upcast());
+        child_source.map(|it| it[self.id.local_id].clone())
+    }
+}