1 files changed, 64 insertions, 0 deletions

diff --git a/crates/ra_analysis/src/macros.rs b/crates/ra_analysis/src/macros.rs
new file mode 100644
index 000000000..c0dd49dc8
--- /dev/null
+++ b/crates/ra_analysis/src/macros.rs
@@ -0,0 +1,64 @@
+/// Begining of macro expansion.
+///
+/// This code should be moved out of ra_analysis into hir (?) ideally.
+use ra_syntax::{ast, AstNode, SourceFileNode, TextRange};
+
+use crate::{db::RootDatabase, FileId};
+
+pub(crate) fn expand(
+    _db: &RootDatabase,
+    _file_id: FileId,
+    macro_call: ast::MacroCall,
+) -> Option<MacroExpansion> {
+    let path = macro_call.path()?;
+    if path.qualifier().is_some() {
+        return None;
+    }
+    let name_ref = path.segment()?.name_ref()?;
+    if name_ref.text() != "ctry" {
+        return None;
+    }
+
+    let arg = macro_call.token_tree()?;
+    let text = format!(
+        r"
+        fn dummy() {{
+            match {} {{
+                None => return Ok(None),
+                Some(it) => it,
+            }}
+        }}",
+        arg.syntax().text()
+    );
+    let file = SourceFileNode::parse(&text);
+    let match_expr = file.syntax().descendants().find_map(ast::MatchExpr::cast)?;
+    let match_arg = match_expr.expr()?;
+    let ranges_map = vec![(arg.syntax().range(), match_arg.syntax().range())];
+    let res = MacroExpansion {
+        source_file: file,
+        ranges_map,
+    };
+    Some(res)
+}
+
+pub(crate) struct MacroExpansion {
+    pub(crate) source_file: SourceFileNode,
+    pub(crate) ranges_map: Vec<(TextRange, TextRange)>,
+}
+
+impl MacroExpansion {
+    pub(crate) fn source_file(&self) -> &SourceFileNode {
+        &self.source_file
+    }
+    pub(crate) fn map_range_back(&self, tgt_range: TextRange) -> Option<TextRange> {
+        for (s_range, t_range) in self.ranges_map.iter() {
+            if tgt_range.is_subrange(&t_range) {
+                let tgt_at_zero_range = tgt_range - tgt_range.start();
+                let tgt_range_offset = tgt_range.start() - t_range.start();
+                let src_range = tgt_at_zero_range + tgt_range_offset + s_range.start();
+                return Some(src_range);
+            }
+        }
+        None
+    }
+}