2 files changed, 43 insertions, 0 deletions

diff --git a/crates/ide_ssr/src/from_comment.rs b/crates/ide_ssr/src/from_comment.rs
new file mode 100644
index 000000000..f1b312284
--- /dev/null
+++ b/crates/ide_ssr/src/from_comment.rs
@@ -0,0 +1,32 @@
+//! This module allows building an SSR MatchFinder by parsing the SSR rule
+//! from a comment.
+
+use ide_db::{
+    base_db::{FilePosition, FileRange, SourceDatabase},
+    RootDatabase,
+};
+use syntax::{
+    ast::{self, AstNode, AstToken},
+    TextRange,
+};
+
+use crate::MatchFinder;
+
+/// Attempts to build an SSR MatchFinder from a comment at the given file
+/// range. If successful, returns the MatchFinder and a TextRange covering
+/// comment.
+pub fn ssr_from_comment(db: &RootDatabase, frange: FileRange) -> Option<(MatchFinder, TextRange)> {
+    let comment = {
+        let file = db.parse(frange.file_id);
+        file.tree().syntax().token_at_offset(frange.range.start()).find_map(ast::Comment::cast)
+    }?;
+    let comment_text_without_prefix = comment.text().strip_prefix(comment.prefix()).unwrap();
+    let ssr_rule = comment_text_without_prefix.parse().ok()?;
+
+    let lookup_context = FilePosition { file_id: frange.file_id, offset: frange.range.start() };
+
+    let mut match_finder = MatchFinder::in_context(db, lookup_context, vec![]);
+    match_finder.add_rule(ssr_rule).ok()?;
+
+    Some((match_finder, comment.syntax().text_range()))
+}
diff --git a/crates/ide_ssr/src/lib.rs b/crates/ide_ssr/src/lib.rs
index a97fc8bca..00585f448 100644
--- a/crates/ide_ssr/src/lib.rs
+++ b/crates/ide_ssr/src/lib.rs
@@ -57,7 +57,17 @@
 //
 // | VS Code | **Rust Analyzer: Structural Search Replace**
 // |===
+//
+// Also available as an assist, by writing a comment containing the structural
+// search and replace rule. You will only see the assist if the comment can
+// be parsed as a valid structural search and replace rule.
+//
+// ```rust
+// // Place the cursor on the line below to see the assist 💡.
+// // foo($a, $b) ==>> ($a).foo($b)
+// ```
 
+mod from_comment;
 mod matching;
 mod nester;
 mod parsing;
@@ -71,6 +81,7 @@ mod tests;
 
 use crate::errors::bail;
 pub use crate::errors::SsrError;
+pub use crate::from_comment::ssr_from_comment;
 pub use crate::matching::Match;
 use crate::matching::MatchFailureReason;
 use hir::Semantics;