1 files changed, 80 insertions, 0 deletions

diff --git a/crates/ra_hir_expand/src/builtin_macro.rs b/crates/ra_hir_expand/src/builtin_macro.rs
new file mode 100644
index 000000000..97fb0cb55
--- /dev/null
+++ b/crates/ra_hir_expand/src/builtin_macro.rs
@@ -0,0 +1,80 @@
+//! Builtin macro
+use crate::db::AstDatabase;
+use crate::{
+    ast::{self, AstNode},
+    name, AstId, CrateId, HirFileId, MacroCallId, MacroDefId, MacroDefKind, MacroFileKind,
+    TextUnit,
+};
+
+use crate::quote;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum BuiltinExpander {
+    Line,
+}
+
+impl BuiltinExpander {
+    pub fn expand(
+        &self,
+        db: &dyn AstDatabase,
+        id: MacroCallId,
+        tt: &tt::Subtree,
+    ) -> Result<tt::Subtree, mbe::ExpandError> {
+        match self {
+            BuiltinExpander::Line => line_expand(db, id, tt),
+        }
+    }
+}
+
+pub fn find_builtin_macro(
+    ident: &name::Name,
+    krate: CrateId,
+    ast_id: AstId<ast::MacroCall>,
+) -> Option<MacroDefId> {
+    // FIXME: Better registering method
+    if ident == &name::LINE_MACRO {
+        Some(MacroDefId { krate, ast_id, kind: MacroDefKind::BuiltIn(BuiltinExpander::Line) })
+    } else {
+        None
+    }
+}
+
+fn to_line_number(db: &dyn AstDatabase, file: HirFileId, pos: TextUnit) -> usize {
+    // FIXME: Use expansion info
+    let file_id = file.original_file(db);
+    let text = db.file_text(file_id);
+    let mut line_num = 1;
+
+    // Count line end
+    for (i, c) in text.chars().enumerate() {
+        if i == pos.to_usize() {
+            break;
+        }
+        if c == '\n' {
+            line_num += 1;
+        }
+    }
+
+    line_num
+}
+
+fn line_expand(
+    db: &dyn AstDatabase,
+    id: MacroCallId,
+    _tt: &tt::Subtree,
+) -> Result<tt::Subtree, mbe::ExpandError> {
+    let loc = db.lookup_intern_macro(id);
+    let macro_call = loc.ast_id.to_node(db);
+
+    let arg = macro_call.token_tree().ok_or_else(|| mbe::ExpandError::UnexpectedToken)?;
+    let arg_start = arg.syntax().text_range().start();
+
+    let file = id.as_file(MacroFileKind::Expr);
+    let line_num = to_line_number(db, file, arg_start);
+
+    let expanded = quote! {
+        #line_num
+    };
+
+    Ok(expanded)
+}