feat: Auto-detect file type in ast command by extension

crates/plotnik-cli/src/cli/commands.rs

@@ -60,19 +60,20 @@ pub fn build_cli() -> Command {
 ///
 /// Accepts all runtime flags for unified CLI experience.
 /// Shows query AST when query is provided, source AST when source is provided.
+/// Single positional file is auto-detected: .ptk → query, otherwise → source.
 pub fn ast_command() -> Command {
     let cmd = Command::new("ast")
         .about("Show AST of query and/or source file")
         .override_usage(
             "\
-  plotnik ast <QUERY> [SOURCE]
+  plotnik ast <FILE>                 # auto-detect by extension
+  plotnik ast <QUERY> <SOURCE>       # both ASTs
   plotnik ast -q <TEXT> [SOURCE]
-  plotnik ast <SOURCE>
   plotnik ast -s <TEXT> -l <LANG>",
         )
         .after_help(
             r#"EXAMPLES:
-  plotnik ast query.ptk               # query AST
+  plotnik ast query.ptk               # query AST (.ptk extension)
   plotnik ast app.ts                  # source AST (tree-sitter)
   plotnik ast query.ptk app.ts        # both ASTs
   plotnik ast query.ptk app.ts --raw  # CST / include anonymous nodes

crates/plotnik-cli/src/cli/dispatch.rs

@@ -39,6 +39,11 @@ impl AstParams {
         let (query_path, source_path) =
             shift_positional_to_source(query_text.is_some(), query_path, source_path);
 
+        // Extension-based detection: when a single file is provided without -q,
+        // .ptk → query, otherwise → source (detect language from extension).
+        let (query_path, source_path) =
+            detect_file_type_by_extension(query_path, source_path, query_text.is_some());
+
         Self {
             query_path,
             query_text,
@@ -352,3 +357,28 @@ fn shift_positional_to_source(
         (query_path, source_path)
     }
 }
+
+/// Detect file type by extension for ast command.
+/// When a single file is provided without -q: .ptk → query, otherwise → source.
+fn detect_file_type_by_extension(
+    query_path: Option<PathBuf>,
+    source_path: Option<PathBuf>,
+    has_query_text: bool,
+) -> (Option<PathBuf>, Option<PathBuf>) {
+    // Only apply when: single positional file, no -q flag, no explicit source
+    if has_query_text || source_path.is_some() {
+        return (query_path, source_path);
+    }
+
+    let Some(path) = query_path else {
+        return (None, None);
+    };
+
+    // .ptk extension → treat as query
+    if path.extension().is_some_and(|ext| ext == "ptk") {
+        return (Some(path), None);
+    }
+
+    // Any other extension → treat as source file
+    (None, Some(path))
+}

crates/plotnik-cli/src/cli/dispatch_tests.rs

@@ -712,3 +712,62 @@ fn check_accepts_raw_flag() {
         result.err()
     );
 }
+
+// Extension-based detection tests for ast command
+
+#[test]
+fn ast_detects_ptk_as_query() {
+    let cmd = ast_command();
+    let result = cmd.try_get_matches_from(["ast", "query.ptk"]);
+    assert!(result.is_ok());
+
+    let m = result.unwrap();
+    let params = AstParams::from_matches(&m);
+
+    // .ptk extension → treat as query
+    assert_eq!(params.query_path, Some(PathBuf::from("query.ptk")));
+    assert_eq!(params.source_path, None);
+}
+
+#[test]
+fn ast_detects_non_ptk_as_source() {
+    let cmd = ast_command();
+    let result = cmd.try_get_matches_from(["ast", "app.js"]);
+    assert!(result.is_ok());
+
+    let m = result.unwrap();
+    let params = AstParams::from_matches(&m);
+
+    // Non-.ptk extension → treat as source
+    assert_eq!(params.query_path, None);
+    assert_eq!(params.source_path, Some(PathBuf::from("app.js")));
+}
+
+#[test]
+fn ast_no_extension_detection_with_two_positionals() {
+    let cmd = ast_command();
+    let result = cmd.try_get_matches_from(["ast", "query.ptk", "app.js"]);
+    assert!(result.is_ok());
+
+    let m = result.unwrap();
+    let params = AstParams::from_matches(&m);
+
+    // Two positionals → first is query, second is source (no detection)
+    assert_eq!(params.query_path, Some(PathBuf::from("query.ptk")));
+    assert_eq!(params.source_path, Some(PathBuf::from("app.js")));
+}
+
+#[test]
+fn ast_no_extension_detection_with_inline_query() {
+    let cmd = ast_command();
+    let result = cmd.try_get_matches_from(["ast", "-q", "(id) @x", "app.js"]);
+    assert!(result.is_ok());
+
+    let m = result.unwrap();
+    let params = AstParams::from_matches(&m);
+
+    // -q provided → positional shift takes precedence, no extension detection
+    assert_eq!(params.query_path, None);
+    assert_eq!(params.query_text, Some("(id) @x".to_string()));
+    assert_eq!(params.source_path, Some(PathBuf::from("app.js")));
+}