From d3ca783562b6ef5d662006e83829dfdc1805fae2 Mon Sep 17 00:00:00 2001
From: Danny McClanahan <1305167+cosmicexplorer@users.noreply.github.com>
Date: Sat, 16 Nov 2024 00:00:38 -0500
Subject: [PATCH] annotate delimiter pairing logic

---
 lib/coffeescript/lexer.js | 11 ++++++++---
 src/lexer.coffee          | 12 ++++++++++--
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/lib/coffeescript/lexer.js b/lib/coffeescript/lexer.js
index b00e651c40..c067570dea 100644
--- a/lib/coffeescript/lexer.js
+++ b/lib/coffeescript/lexer.js
@@ -1103,7 +1103,7 @@
     // here. `;` and newlines are both treated as a `TERMINATOR`, we distinguish
     // parentheses that indicate a method call from regular parentheses, and so on.
     literalToken() {
-      var match, message, origin, prev, ref, ref1, ref2, ref3, ref4, ref5, skipToken, tag, token, value;
+      var match, message, origin, prev, ref, ref1, ref2, ref3, ref4, ref5, skipToken, tag, value;
       if (match = OPERATOR.exec(this.chunk)) {
         [value] = match;
         if (CODE.test(value)) {
@@ -1187,14 +1187,19 @@
           }
         }
       }
-      token = this.makeToken(tag, value);
+      // Match up paired delimiters.
       switch (value) {
+        // Upon opening a pair, provide the requisite close token, and record the "origin" as
+        // a separate token.
         case '(':
         case '{':
         case '[':
+          // TODO: this concept of "origin" is somewhat overloaded and makes it difficult to introspect
+          //       a token stream. Is it the source of a generated token, or the "parent" node for
+          //       a context-sensitive match like paired delimiters?
           this.ends.push({
             tag: INVERSES[value],
-            origin: token
+            origin: this.makeToken(tag, value)
           });
           break;
         case ')':
diff --git a/src/lexer.coffee b/src/lexer.coffee
index 80135b9db5..d2a3cd35da 100644
--- a/src/lexer.coffee
+++ b/src/lexer.coffee
@@ -815,10 +815,18 @@ exports.Lexer = class Lexer
         tag = 'INDEX_START'
         switch prev[0]
           when '?'  then prev[0] = 'INDEX_SOAK'
-    token = @makeToken tag, value
+
+    # Match up paired delimiters.
     switch value
-      when '(', '{', '[' then @ends.push {tag: INVERSES[value], origin: token}
+      # Upon opening a pair, provide the requisite close token, and record the "origin" as
+      # a separate token.
+      when '(', '{', '['
+        # TODO: this concept of "origin" is somewhat overloaded and makes it difficult to introspect
+        #       a token stream. Is it the source of a generated token, or the "parent" node for
+        #       a context-sensitive match like paired delimiters?
+        @ends.push {tag: INVERSES[value], origin: @makeToken tag, value}
       when ')', '}', ']' then @pair value
+
     @tokens.push @makeToken tag, value
     value.length