Fix lambda stable names check.

Author: cstancu

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/lambda/LambdaProxyRenamingSubstitutionProcessor.java

@@ -71,9 +71,16 @@ private LambdaSubstitutionType getSubstitution(ResolvedJavaType original) {
     }
 
     /**
-     * Finds a unique name for a lambda proxies with a same target originating from the same class.
-     *
-     * NOTE: the name truly stable only in a single threaded build.
+     * Finds a unique name for lambda proxies with the same target originating from the same class.
+     * Method {@link LambdaUtils#findStableLambdaName(ResolvedJavaType)} hashes over a lambda type
+     * descriptor (invoked methods, constructor parameters, implemented interfaces) in an effort to
+     * find enough differences that can yield a unique name. However, this can still lead to
+     * conflicts. To create unique names when conflicts are found the naming scheme uses a counter:
+     * first a 0 is added to the end of the generated lambda name, and it is incremented until a
+     * unique name is found. This also means that the name is truly stable only in a single threaded
+     * build, i.e., when conflicts are discovered in the same order. Since the conflict counter
+     * doesn't have an upper limit the generated lambda name length can vary but the base hash is
+     * always 32 hex digits long.
      */
     private String findUniqueLambdaProxyName(String lambdaTargetName) {
         synchronized (uniqueLambdaProxyNames) {
@@ -91,7 +98,22 @@ private String findUniqueLambdaProxyName(String lambdaTargetName) {
         }
     }
 
+    /**
+     * Find the base name generated by {@link LambdaUtils#findStableLambdaName(ResolvedJavaType)} by
+     * subtracting the counter injected by {@link #findUniqueLambdaProxyName(String)}. Note that the
+     * counter can be on multiple digits but the base hash is always 32 hex digits long.
+     */
+    private static String getBaseName(String lambdaTargetName) {
+        int startIndexOfHash = lambdaTargetName.indexOf(LambdaUtils.ADDRESS_PREFIX) + LambdaUtils.ADDRESS_PREFIX.length();
+        return lambdaTargetName.substring(0, startIndexOfHash + 32);
+    }
+
+    /**
+     * Check if this lambda's name conflicted with any other entries, i.e., if the conflict counter
+     * ever got to 1.
+     */
     public boolean isNameAlwaysStable(String lambdaTargetName) {
-        return !uniqueLambdaProxyNames.contains(lambdaTargetName.substring(0, lambdaTargetName.length() - 1) + "1;");
+        String baseName = getBaseName(lambdaTargetName);
+        return !uniqueLambdaProxyNames.contains(baseName + "1;");
     }
 }