1 files changed, 66 insertions, 0 deletions

diff --git a/crates/hir_expand/src/hygiene.rs b/crates/hir_expand/src/hygiene.rs
new file mode 100644
index 000000000..845e9cbc1
--- /dev/null
+++ b/crates/hir_expand/src/hygiene.rs
@@ -0,0 +1,66 @@
+//! This modules handles hygiene information.
+//!
+//! Specifically, `ast` + `Hygiene` allows you to create a `Name`. Note that, at
+//! this moment, this is horribly incomplete and handles only `$crate`.
+use base_db::CrateId;
+use either::Either;
+use syntax::ast;
+
+use crate::{
+    db::AstDatabase,
+    name::{AsName, Name},
+    HirFileId, HirFileIdRepr, MacroCallId, MacroDefKind,
+};
+
+#[derive(Clone, Debug)]
+pub struct Hygiene {
+    // This is what `$crate` expands to
+    def_crate: Option<CrateId>,
+
+    // Indicate this is a local inner macro
+    local_inner: bool,
+}
+
+impl Hygiene {
+    pub fn new(db: &dyn AstDatabase, file_id: HirFileId) -> Hygiene {
+        let (def_crate, local_inner) = match file_id.0 {
+            HirFileIdRepr::FileId(_) => (None, false),
+            HirFileIdRepr::MacroFile(macro_file) => match macro_file.macro_call_id {
+                MacroCallId::LazyMacro(id) => {
+                    let loc = db.lookup_intern_macro(id);
+                    match loc.def.kind {
+                        MacroDefKind::Declarative => (loc.def.krate, loc.def.local_inner),
+                        MacroDefKind::BuiltIn(_) => (None, false),
+                        MacroDefKind::BuiltInDerive(_) => (None, false),
+                        MacroDefKind::BuiltInEager(_) => (None, false),
+                        MacroDefKind::CustomDerive(_) => (None, false),
+                    }
+                }
+                MacroCallId::EagerMacro(_id) => (None, false),
+            },
+        };
+        Hygiene { def_crate, local_inner }
+    }
+
+    pub fn new_unhygienic() -> Hygiene {
+        Hygiene { def_crate: None, local_inner: false }
+    }
+
+    // FIXME: this should just return name
+    pub fn name_ref_to_name(&self, name_ref: ast::NameRef) -> Either<Name, CrateId> {
+        if let Some(def_crate) = self.def_crate {
+            if name_ref.text() == "$crate" {
+                return Either::Right(def_crate);
+            }
+        }
+        Either::Left(name_ref.as_name())
+    }
+
+    pub fn local_inner_macros(&self) -> Option<CrateId> {
+        if self.local_inner {
+            self.def_crate
+        } else {
+            None
+        }
+    }
+}