github · asgerf · Jun 12, 2026 · Jun 12, 2026 · Jun 12, 2026 · Jun 12, 2026
@@ -333,6 +333,9 @@ pub fn extract(
             .run_from_tree(&tree, source)
             .unwrap_or_else(|e| panic!("Desugaring failed for {path_str}: {e}"));
         traverse_yeast(&ast, &mut visitor);
+        // Comments and other `extra` nodes are not represented in the desugared
+        // AST, so recover them directly from the original parse tree.
+        traverse_extras(&tree, &mut visitor);
     } else {
         traverse(&tree, &mut visitor);
     }
@@ -365,6 +368,8 @@ struct Visitor<'a> {
     ast_node_parent_table_name: String,
     /// Language-specific name of the tokeninfo table
     tokeninfo_table_name: String,
+    /// Language-specific name of the trivia tokeninfo table
+    trivia_tokeninfo_table_name: String,
     /// A lookup table from type name to node types
     schema: &'a NodeTypeMap,
     /// A stack for gathering information from child nodes. Whenever a node is
@@ -395,11 +400,33 @@ impl<'a> Visitor<'a> {
             ast_node_location_table_name: format!("{language_prefix}_ast_node_location"),
             ast_node_parent_table_name: format!("{language_prefix}_ast_node_parent"),
             tokeninfo_table_name: format!("{language_prefix}_tokeninfo"),
+            trivia_tokeninfo_table_name: format!("{language_prefix}_trivia_tokeninfo"),
             schema,
             stack: Vec::new(),
         }
     }
 
+    /// Emits a `TriviaToken` for the given `extra` node (e.g. a comment) from
+    /// the original parse tree. Trivia tokens carry a location and their source
+    /// text, but are not attached to a parent in the (possibly desugared) AST.
+    fn emit_trivia_token(&mut self, node: &Node) {
+        let id = self.trap_writer.fresh_id();
+        let loc = location_for(self, self.file_label, node);
+        let loc_label = location_label(self.trap_writer, loc);
+        self.trap_writer.add_tuple(
+            &self.ast_node_location_table_name,
+            vec![trap::Arg::Label(id), trap::Arg::Label(loc_label)],
+        );
+        self.trap_writer.add_tuple(
+            &self.trivia_tokeninfo_table_name,
+            vec![
+                trap::Arg::Label(id),
+                trap::Arg::Int(node.kind_id() as usize),
+                sliced_source_arg(self.source, node),
+            ],
+        );
+    }
+
     fn record_parse_error(&mut self, loc: trap::Label, mesg: &diagnostics::DiagnosticMessage) {
         self.diagnostics_writer.write(mesg);
         let id = self.trap_writer.fresh_id();
@@ -835,6 +862,24 @@ fn traverse(tree: &Tree, visitor: &mut Visitor) {
     }
 }
 
+/// Walks the original tree-sitter tree and emits a `TriviaToken` for every
+/// `extra` node (e.g. a comment). Used to preserve comments that would
+/// otherwise be lost after a desugaring pass rewrites the tree.
+fn traverse_extras(tree: &Tree, visitor: &mut Visitor) {
+    emit_extras_in(visitor, tree.root_node());
+}
+
+fn emit_extras_in(visitor: &mut Visitor, node: Node<'_>) {
+    let mut cursor = node.walk();
+    for child in node.children(&mut cursor) {
+        if child.is_extra() {
+            visitor.emit_trivia_token(&child);
+        } else {
+            emit_extras_in(visitor, child);
+        }
+    }
+}
+
 fn traverse_yeast(tree: &yeast::Ast, visitor: &mut Visitor) {
     use yeast::Cursor;
     let mut cursor = tree.walk();

@@ -68,7 +68,12 @@ pub fn generate(
         let node_parent_table_name = format!("{}_ast_node_parent", &prefix);
         let token_name = format!("{}_token", &prefix);
         let tokeninfo_name = format!("{}_tokeninfo", &prefix);
+        let trivia_token_name = format!("{}_trivia_token", &prefix);
+        let trivia_tokeninfo_name = format!("{}_trivia_tokeninfo", &prefix);
         let reserved_word_name = format!("{}_reserved_word", &prefix);
+        // When a desugaring is configured, comments and other `extra` nodes are
+        // preserved from the original parse tree as `TriviaToken`s.
+        let has_trivia_tokens = language.desugar.is_some();
         let effective_node_types: String = match language
             .desugar
             .as_ref()
@@ -85,28 +90,35 @@ pub fn generate(
         let nodes = node_types::read_node_types_str(&prefix, &effective_node_types)?;
         let (dbscheme_entries, mut ast_node_members, token_kinds) = convert_nodes(&nodes);
         ast_node_members.insert(&token_name);
+        if has_trivia_tokens {
+            ast_node_members.insert(&trivia_token_name);
+        }
         writeln!(&mut dbscheme_writer, "/*- {} dbscheme -*/", language.name)?;
         dbscheme::write(&mut dbscheme_writer, &dbscheme_entries)?;
         let token_case = create_token_case(&token_name, token_kinds);
-        dbscheme::write(
-            &mut dbscheme_writer,
-            &[
-                dbscheme::Entry::Table(create_tokeninfo(&tokeninfo_name, &token_name)),
-                dbscheme::Entry::Case(token_case),
-                dbscheme::Entry::Union(dbscheme::Union {
-                    name: &ast_node_name,
-                    members: ast_node_members,
-                }),
-                dbscheme::Entry::Table(create_ast_node_location_table(
-                    &node_location_table_name,
-                    &ast_node_name,
-                )),
-                dbscheme::Entry::Table(create_ast_node_parent_table(
-                    &node_parent_table_name,
-                    &ast_node_name,
-                )),
-            ],
-        )?;
+        let mut dbscheme_tail = vec![
+            dbscheme::Entry::Table(create_tokeninfo(&tokeninfo_name, &token_name)),
+            dbscheme::Entry::Case(token_case),
+        ];
+        if has_trivia_tokens {
+            dbscheme_tail.push(dbscheme::Entry::Table(create_tokeninfo(
+                &trivia_tokeninfo_name,
+                &trivia_token_name,
+            )));
+        }
+        dbscheme_tail.push(dbscheme::Entry::Union(dbscheme::Union {
+            name: &ast_node_name,
+            members: ast_node_members,
+        }));
+        dbscheme_tail.push(dbscheme::Entry::Table(create_ast_node_location_table(
+            &node_location_table_name,
+            &ast_node_name,
+        )));
+        dbscheme_tail.push(dbscheme::Entry::Table(create_ast_node_parent_table(
+            &node_parent_table_name,
+            &ast_node_name,
+        )));
+        dbscheme::write(&mut dbscheme_writer, &dbscheme_tail)?;
 
         let mut body = vec![
             ql::TopLevel::Class(ql_gen::create_ast_node_class(
@@ -116,6 +128,12 @@ pub fn generate(
             )),
             ql::TopLevel::Class(ql_gen::create_token_class(&token_name, &tokeninfo_name)),
         ];
+        if has_trivia_tokens {
+            body.push(ql::TopLevel::Class(ql_gen::create_trivia_token_class(
+                &trivia_token_name,
+                &trivia_tokeninfo_name,
+            )));
+        }
         // Only emit the ReservedWord class when there are actually unnamed token
         // types in the schema (i.e., @{prefix}_reserved_word exists in the dbscheme).
         // When converting from a YEAST YAML schema that has no unnamed tokens, this

@@ -199,6 +199,70 @@ pub fn create_token_class<'a>(token_type: &'a str, tokeninfo: &'a str) -> ql::Cl
     }
 }
 
+/// Creates the `TriviaToken` class. Trivia tokens (e.g. comments) are
+/// `extra` nodes preserved from the original parse tree even when the tree has
+/// been rewritten by a desugaring pass. They are not part of the regular
+/// `Token` hierarchy because they do not appear in the (possibly desugared)
+/// output schema.
+pub fn create_trivia_token_class<'a>(
+    trivia_token_type: &'a str,
+    trivia_tokeninfo: &'a str,
+) -> ql::Class<'a> {
+    let trivia_tokeninfo_arity = 3; // id, kind, value
+    let get_value = ql::Predicate {
+        qldoc: Some(String::from("Gets the source text of this trivia token.")),
+        name: "getValue",
+        overridden: false,
+        is_private: false,
+        is_final: true,
+        return_type: Some(ql::Type::String),
+        formal_parameters: vec![],
+        body: create_get_field_expr_for_column_storage(
+            "result",
+            trivia_tokeninfo,
+            1,
+            trivia_tokeninfo_arity,
+        ),
+        overlay: None,
+    };
+    let to_string = ql::Predicate {
+        qldoc: Some(String::from(
+            "Gets a string representation of this element.",
+        )),
+        name: "toString",
+        overridden: true,
+        is_private: false,
+        is_final: true,
+        return_type: Some(ql::Type::String),
+        formal_parameters: vec![],
+        body: ql::Expression::Equals(
+            Box::new(ql::Expression::Var("result")),
+            Box::new(ql::Expression::Dot(
+                Box::new(ql::Expression::Var("this")),
+                "getValue",
+                vec![],
+            )),
+        ),
+        overlay: None,
+    };
+    ql::Class {
+        qldoc: Some(String::from(
+            "A trivia token, such as a comment, preserved from the original parse tree.",
+        )),
+        name: "TriviaToken",
+        is_abstract: false,
+        supertypes: vec![ql::Type::At(trivia_token_type), ql::Type::Normal("AstNode")]
+            .into_iter()
+            .collect(),
+        characteristic_predicate: None,
+        predicates: vec![
+            get_value,
+            to_string,
+            create_get_a_primary_ql_class("TriviaToken", false),
+        ],
+    }
+}
+
 // Creates the `ReservedWord` class.
 pub fn create_reserved_word_class(db_name: &str) -> ql::Class<'_> {
     let class_name = "ReservedWord";

@@ -61,6 +61,18 @@ module Unified {
     override string getAPrimaryQlClass() { result = "Token" }
   }
 
+  /** A trivia token, such as a comment, preserved from the original parse tree. */
+  class TriviaToken extends @unified_trivia_token, AstNode {
+    /** Gets the source text of this trivia token. */
+    final string getValue() { unified_trivia_tokeninfo(this, _, result) }
+
+    /** Gets a string representation of this element. */
+    final override string toString() { result = this.getValue() }
+
+    /** Gets the name of the primary QL class for this element. */
+    override string getAPrimaryQlClass() { result = "TriviaToken" }
+  }
+
   /** Gets the file containing the given `node`. */
   private @file getNodeFile(@unified_ast_node node) {
     exists(@location_default loc | unified_ast_node_location(node, loc) |

@@ -0,0 +1,18 @@
+/** Provides classes for working with comments. */
+
+private import unified
+
+/**
+ * A comment appearing in the source code.
+ */
+class Comment extends TriviaToken {
+  // At the moment, comments are the only type trivia token we extract
+  /**
+   * Gets the text inside this comment, not counting the delimeters.
+   */
+  string getCommentText() {
+    result = this.getValue().regexpCapture("//(.*)", 1)
+    or
+    result = this.getValue().regexpCapture("(?s)/\\*(.*)\\*/", 1)
+  }
+}
@@ -334,7 +334,13 @@ case @unified_token.kind of
 ;
 
 
-@unified_ast_node = @unified_apply_pattern | @unified_binary_expr | @unified_block_stmt | @unified_call_expr | @unified_expr_condition | @unified_expr_stmt | @unified_guard_if_stmt | @unified_if_stmt | @unified_lambda_expr | @unified_let_pattern_condition | @unified_member_access_expr | @unified_name_expr | @unified_parameter | @unified_sequence_condition | @unified_token | @unified_top_level | @unified_tuple_pattern | @unified_unary_expr | @unified_var_pattern | @unified_variable_declaration_stmt | @unified_variable_declarator
+unified_trivia_tokeninfo(
+  unique int id: @unified_trivia_token,
+  int kind: int ref,
+  string value: string ref
+);
+
+@unified_ast_node = @unified_apply_pattern | @unified_binary_expr | @unified_block_stmt | @unified_call_expr | @unified_expr_condition | @unified_expr_stmt | @unified_guard_if_stmt | @unified_if_stmt | @unified_lambda_expr | @unified_let_pattern_condition | @unified_member_access_expr | @unified_name_expr | @unified_parameter | @unified_sequence_condition | @unified_token | @unified_top_level | @unified_trivia_token | @unified_tuple_pattern | @unified_unary_expr | @unified_var_pattern | @unified_variable_declaration_stmt | @unified_variable_declarator
 
 unified_ast_node_location(
   unique int node: @unified_ast_node ref,

@@ -0,0 +1,8 @@
+/**
+ * Provides classes for working with the AST, as well as files and locations.
+ */
+
+import codeql.Locations
+import codeql.files.FileSystem
+import codeql.unified.Ast::Unified
+import codeql.unified.Comments
@@ -0,0 +1,3 @@
+| comments.swift:1:1:1:22 | // Hello this is swift |  Hello this is swift |
+| comments.swift:3:1:6:3 | /*\n * This is a multi-line comment\n * It should be ignored by the parser\n */ | \n * This is a multi-line comment\n * It should be ignored by the parser\n  |
+| comments.swift:9:5:9:36 | // This is a single-line comment |  This is a single-line comment |
@@ -0,0 +1,3 @@
+import unified
+
+query predicate comments(Comment c, string text) { text = c.getCommentText() }
@@ -0,0 +1,11 @@
+// Hello this is swift
+
+/*
+ * This is a multi-line comment
+ * It should be ignored by the parser
+ */
+
+func hello() {
+    // This is a single-line comment
+    print("Hello, world!")
+}
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		import unified

		query predicate comments(Comment c, string text) { text = c.getCommentText() }