[JSC] SourceCodeKey::operator== must compare the source text again

JSTests/modules/code-cache-key-compares-source.js

@@ -0,0 +1,15 @@
+import { shouldBe } from "./resources/assert.js";
+import { value as first } from "./code-cache-key-compares-source/first.js";
+import { value as second } from "./code-cache-key-compares-source/second.js";
+
+// first.js and second.js are the same length and their source text has the
+// same StringImpl hash (24 bits of RapidHash, 0xd438ab), so they produce equal
+// SourceCodeKey hashes. SourceCodeKey::operator== has to fall back to comparing
+// the source text, otherwise the CodeCache hands second.js the
+// UnlinkedModuleProgramCodeBlock compiled for first.js and second.js silently
+// evaluates first.js's code. Both files must stay byte-for-byte as they are
+// (no comments, no whitespace changes) or they stop colliding; a replacement
+// pair can be found by hashing candidate sources with
+// StringHasher::computeHashAndMaskTop8Bits until two of them match.
+shouldBe(first, 10001215);
+shouldBe(second, 10006987);

JSTests/modules/code-cache-key-compares-source/first.js

@@ -0,0 +1 @@
+export const value = 10001215;

JSTests/modules/code-cache-key-compares-source/second.js

@@ -0,0 +1 @@
+export const value = 10006987;

Source/JavaScriptCore/parser/SourceCodeKey.h

@@ -117,11 +117,7 @@ class SourceCodeKey {
             && m_functionConstructorParametersEndPosition == other.m_functionConstructorParametersEndPosition
             && m_name == other.m_name
             && host() == other.host()
-#if USE(BUN_JSC_ADDITIONS)
-            ;
-#else
             && (m_sourceCode == other.m_sourceCode || string() == other.string());
-#endif
     }
 
     struct HashTraits : SimpleClassHashTraits<SourceCodeKey> {