Add simple CLI command for running tree queries

cli/src/query.rs

@@ -0,0 +1,49 @@
+use super::error::{Error, Result};
+use std::fs;
+use std::io::{self, Write};
+use std::path::Path;
+use tree_sitter::{Language, Parser, Query};
+
+pub fn query_files_at_paths(
+    language: Language,
+    paths: Vec<&Path>,
+    query_path: &Path,
+) -> Result<()> {
+    let stdout = io::stdout();
+    let mut stdout = stdout.lock();
+
+    let query_source = fs::read_to_string(query_path).map_err(Error::wrap(|| {
+        format!("Error reading query file {:?}", query_path)
+    }))?;
+    let query = Query::new(language, &query_source)
+        .map_err(|e| Error::new(format!("Query compilation failed: {:?}", e)))?;
+
+    let query_context = query.context();
+
+    let mut parser = Parser::new();
+    parser.set_language(language).map_err(|e| e.to_string())?;
+
+    for path in paths {
+        writeln!(&mut stdout, "{}", path.to_str().unwrap())?;
+
+        let source_code = fs::read(path).map_err(Error::wrap(|| {
+            format!("Error reading source file {:?}", path)
+        }))?;
+
+        let tree = parser.parse(&source_code, None).unwrap();
+
+        for mat in query_context.exec(tree.root_node()) {
+            writeln!(&mut stdout, "  pattern: {}", mat.pattern_index())?;
+            for (capture_id, node) in mat.captures() {
+                writeln!(
+                    &mut stdout,
+                    "    {}: {:?}",
+                    &query.capture_names()[capture_id],
+                    node.utf8_text(&source_code).unwrap_or("")
+                )?;
+            }
+        }
+    }
+
+    Ok(())
+}