2 files changed, 277 insertions, 0 deletions

diff --git a/crates/ra_hir_def/src/child_from_source.rs b/crates/ra_hir_def/src/child_from_source.rs
new file mode 100644
index 000000000..37d4b7870
--- /dev/null
+++ b/crates/ra_hir_def/src/child_from_source.rs
@@ -0,0 +1,276 @@
+//! When *constructing* `hir`, we start at some parent syntax node and recursively
+//! lower the children.
+//!
+//! This modules allows one to go in the opposite direction: start with a syntax
+//! node for a *child*, and get its hir.
+
+use either::Either;
+use hir_expand::InFile;
+use ra_syntax::{ast, AstNode, AstPtr};
+
+use crate::{
+    db::DefDatabase,
+    src::{HasChildSource, HasSource},
+    AssocItemId, ConstId, EnumId, EnumVariantId, FunctionId, ImplId, Lookup, ModuleDefId, ModuleId,
+    StaticId, StructFieldId, TraitId, TypeAliasId, VariantId,
+};
+
+pub trait ChildFromSource<CHILD, SOURCE> {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<SOURCE>,
+    ) -> Option<CHILD>;
+}
+
+impl ChildFromSource<FunctionId, ast::FnDef> for TraitId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::FnDef>,
+    ) -> Option<FunctionId> {
+        let data = db.trait_data(*self);
+        data.items
+            .iter()
+            .filter_map(|(_, item)| match item {
+                AssocItemId::FunctionId(it) => Some(*it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            })
+    }
+}
+
+impl ChildFromSource<FunctionId, ast::FnDef> for ImplId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::FnDef>,
+    ) -> Option<FunctionId> {
+        let data = db.impl_data(*self);
+        data.items
+            .iter()
+            .filter_map(|item| match item {
+                AssocItemId::FunctionId(it) => Some(*it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            })
+    }
+}
+
+impl ChildFromSource<FunctionId, ast::FnDef> for ModuleId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::FnDef>,
+    ) -> Option<FunctionId> {
+        let crate_def_map = db.crate_def_map(self.krate);
+        let res = crate_def_map[self.local_id]
+            .scope
+            .declarations()
+            .filter_map(|item| match item {
+                ModuleDefId::FunctionId(it) => Some(it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            });
+        res
+    }
+}
+
+impl ChildFromSource<ConstId, ast::ConstDef> for TraitId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::ConstDef>,
+    ) -> Option<ConstId> {
+        let data = db.trait_data(*self);
+        data.items
+            .iter()
+            .filter_map(|(_, item)| match item {
+                AssocItemId::ConstId(it) => Some(*it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            })
+    }
+}
+
+impl ChildFromSource<ConstId, ast::ConstDef> for ImplId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::ConstDef>,
+    ) -> Option<ConstId> {
+        let data = db.impl_data(*self);
+        data.items
+            .iter()
+            .filter_map(|item| match item {
+                AssocItemId::ConstId(it) => Some(*it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            })
+    }
+}
+
+impl ChildFromSource<ConstId, ast::ConstDef> for ModuleId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::ConstDef>,
+    ) -> Option<ConstId> {
+        let crate_def_map = db.crate_def_map(self.krate);
+        let res = crate_def_map[self.local_id]
+            .scope
+            .declarations()
+            .filter_map(|item| match item {
+                ModuleDefId::ConstId(it) => Some(it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            });
+        res
+    }
+}
+
+impl ChildFromSource<TypeAliasId, ast::TypeAliasDef> for TraitId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::TypeAliasDef>,
+    ) -> Option<TypeAliasId> {
+        let data = db.trait_data(*self);
+        data.items
+            .iter()
+            .filter_map(|(_, item)| match item {
+                AssocItemId::TypeAliasId(it) => Some(*it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            })
+    }
+}
+
+impl ChildFromSource<TypeAliasId, ast::TypeAliasDef> for ImplId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::TypeAliasDef>,
+    ) -> Option<TypeAliasId> {
+        let data = db.impl_data(*self);
+        data.items
+            .iter()
+            .filter_map(|item| match item {
+                AssocItemId::TypeAliasId(it) => Some(*it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            })
+    }
+}
+
+impl ChildFromSource<TypeAliasId, ast::TypeAliasDef> for ModuleId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::TypeAliasDef>,
+    ) -> Option<TypeAliasId> {
+        let crate_def_map = db.crate_def_map(self.krate);
+        let res = crate_def_map[self.local_id]
+            .scope
+            .declarations()
+            .filter_map(|item| match item {
+                ModuleDefId::TypeAliasId(it) => Some(it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            });
+        res
+    }
+}
+
+impl ChildFromSource<StaticId, ast::StaticDef> for ModuleId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::StaticDef>,
+    ) -> Option<StaticId> {
+        let crate_def_map = db.crate_def_map(self.krate);
+        let res = crate_def_map[self.local_id]
+            .scope
+            .declarations()
+            .filter_map(|item| match item {
+                ModuleDefId::StaticId(it) => Some(it),
+                _ => None,
+            })
+            .find(|func| {
+                let source = func.lookup(db).source(db);
+                same_source(&source, &child_source)
+            });
+        res
+    }
+}
+
+impl ChildFromSource<StructFieldId, Either<ast::TupleFieldDef, ast::RecordFieldDef>> for VariantId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<Either<ast::TupleFieldDef, ast::RecordFieldDef>>,
+    ) -> Option<StructFieldId> {
+        let arena_map = self.child_source(db);
+        let (local_id, _) = arena_map.as_ref().value.iter().find(|(_local_id, source)| {
+            child_source.file_id == arena_map.file_id
+                && match (source, &child_source.value) {
+                    (Either::Left(a), Either::Left(b)) => AstPtr::new(a) == AstPtr::new(b),
+                    (Either::Right(a), Either::Right(b)) => AstPtr::new(a) == AstPtr::new(b),
+                    _ => false,
+                }
+        })?;
+        Some(StructFieldId { parent: *self, local_id })
+    }
+}
+
+impl ChildFromSource<EnumVariantId, ast::EnumVariant> for EnumId {
+    fn child_from_source(
+        &self,
+        db: &impl DefDatabase,
+        child_source: InFile<ast::EnumVariant>,
+    ) -> Option<EnumVariantId> {
+        let arena_map = self.child_source(db);
+        let (local_id, _) = arena_map.as_ref().value.iter().find(|(_local_id, source)| {
+            child_source.file_id == arena_map.file_id
+                && AstPtr::new(*source) == AstPtr::new(&child_source.value)
+        })?;
+        Some(EnumVariantId { parent: *self, local_id })
+    }
+}
+
+/// 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 guarantee, but, for
+/// the time being, we will use identity-less AstPtr comparison.
+fn same_source<N: AstNode>(s1: &InFile<N>, s2: &InFile<N>) -> bool {
+    s1.as_ref().map(AstPtr::new) == s2.as_ref().map(AstPtr::new)
+}
diff --git a/crates/ra_hir_def/src/lib.rs b/crates/ra_hir_def/src/lib.rs
index cfeacfded..e02622f62 100644
--- a/crates/ra_hir_def/src/lib.rs
+++ b/crates/ra_hir_def/src/lib.rs
@@ -30,6 +30,7 @@ mod trace;
 pub mod nameres;
 
 pub mod src;
+pub mod child_from_source;
 
 #[cfg(test)]
 mod test_db;