From 6d366bc88042fcd99cd47b731dcb9d623a53cb31 Mon Sep 17 00:00:00 2001
From: Trevor Paley <10186337+TheUnlocked@users.noreply.github.com>
Date: Fri, 19 Apr 2024 19:30:34 -0700
Subject: [PATCH] Fix some edge cases in incremental parsing

---
 package.json                      |  2 +-
 src/parser/parser.ts              | 14 +++++++++++++-
 tests/grammar/incremental.spec.ts | 11 +++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/package.json b/package.json
index 2086e4d..8de523f 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@necode-org/mike",
-  "version": "0.3.7",
+  "version": "0.3.8",
   "author": {
     "name": "Trevor Paley",
     "url": "https://github.com/TheUnlocked"
diff --git a/src/parser/parser.ts b/src/parser/parser.ts
index 232d2e5..944a34a 100644
--- a/src/parser/parser.ts
+++ b/src/parser/parser.ts
@@ -162,8 +162,20 @@ export class Parser extends DiagnosticsMixin implements Rules {
 
         const { insertedTokens, removedTokens } = this.lexer.mutate(firstTokenIdx, numTokens, fullInsertion);
 
+        // Need to also invalidate the previous (non-trivia) token for cases where
+        // a new token can modify an earlier AST node. For example:
+        //      if true {
+        //      
+        //      }
+        //      els[e] {
+        //      
+        //      }
+        // Inserting the 'e' changes it from an identifier and a parse error into an else branch of the
+        // previous if statement. Without invalidating the previous if statement, we couldn't determine that.
+        const firstRemovedTokenIdx = this.tokens.slice(0, firstTokenIdx).findLastIndex(x => !isTrivia(x));
+
         // Cache invalidation
-        for (const token of removedTokens) {
+        for (const token of this.tokens.slice(firstRemovedTokenIdx, firstTokenIdx).concat(removedTokens)) {
             let node = this.memoTable.get(token)?.[0]?.node;
             this.memoTable.delete(token);
 
diff --git a/tests/grammar/incremental.spec.ts b/tests/grammar/incremental.spec.ts
index 8eb65dc..f9e20a6 100644
--- a/tests/grammar/incremental.spec.ts
+++ b/tests/grammar/incremental.spec.ts
@@ -211,6 +211,17 @@ export default () => describe('incremental', () => {
         }
     `;
 
+    testIncremental('modify identifier to create else keyword')`
+        on foo() {
+            if true {
+
+            }
+            els${['', 'e']} {
+
+            }
+        }
+    `;
+
     it('should be a no-op if a mutation is reversed', () => {
         const p1 = new Parser();
         //            0    5    10   15   20   25   30   35   40