1 files changed, 63 insertions, 0 deletions

diff --git a/crates/ra_ide/src/expand.rs b/crates/ra_ide/src/expand.rs
new file mode 100644
index 000000000..2f1abf509
--- /dev/null
+++ b/crates/ra_ide/src/expand.rs
@@ -0,0 +1,63 @@
+//! Utilities to work with files, produced by macros.
+use std::iter::successors;
+
+use hir::Source;
+use ra_db::FileId;
+use ra_syntax::{ast, AstNode, SyntaxNode, SyntaxToken};
+
+use crate::{db::RootDatabase, FileRange};
+
+pub(crate) fn original_range(db: &RootDatabase, node: Source<&SyntaxNode>) -> FileRange {
+    let expansion = match node.file_id.expansion_info(db) {
+        None => {
+            return FileRange {
+                file_id: node.file_id.original_file(db),
+                range: node.value.text_range(),
+            }
+        }
+        Some(it) => it,
+    };
+    // FIXME: the following completely wrong.
+    //
+    // *First*, we should try to map first and last tokens of node, and, if that
+    // fails, return the range of the overall macro expansions.
+    //
+    // *Second*, we should handle recurside macro expansions
+
+    let token = node
+        .value
+        .descendants_with_tokens()
+        .filter_map(|it| it.into_token())
+        .find_map(|it| expansion.map_token_up(node.with_value(&it)));
+
+    match token {
+        Some(it) => {
+            FileRange { file_id: it.file_id.original_file(db), range: it.value.text_range() }
+        }
+        None => {
+            FileRange { file_id: node.file_id.original_file(db), range: node.value.text_range() }
+        }
+    }
+}
+
+pub(crate) fn descend_into_macros(
+    db: &RootDatabase,
+    file_id: FileId,
+    token: SyntaxToken,
+) -> Source<SyntaxToken> {
+    let src = Source::new(file_id.into(), token);
+
+    successors(Some(src), |token| {
+        let macro_call = token.value.ancestors().find_map(ast::MacroCall::cast)?;
+        let tt = macro_call.token_tree()?;
+        if !token.value.text_range().is_subrange(&tt.syntax().text_range()) {
+            return None;
+        }
+        let source_analyzer =
+            hir::SourceAnalyzer::new(db, token.with_value(token.value.parent()).as_ref(), None);
+        let exp = source_analyzer.expand(db, token.with_value(&macro_call))?;
+        exp.map_token_down(db, token.as_ref())
+    })
+    .last()
+    .unwrap()
+}