8368331: ClassFile Signature parsing fails for type parameter with no supertype

src/java.base/share/classes/jdk/internal/classfile/impl/SignaturesImpl.java

@@ -113,8 +113,22 @@ private List<TypeParam> parseParamTypes() {
                 RefTypeSig classBound = null;
                 ArrayList<RefTypeSig> interfaceBounds = null;
                 require(':');
-                if (sig.charAt(sigp) != ':')
-                    classBound = referenceTypeSig();
+                if (sig.charAt(sigp) != ':') {
+                    int p = nextIdentifierEnd(sig, sigp);
+                    // For non-identifier chars:
+                    // . / < indicates class type (inner, package, type arg)
+                    // [ indicates array type
+                    // ; indicates class/type var type
+                    // > and : are illegal, such as in <P:R:>
+                    if (p < sig.length()) {
+                        char limit = sig.charAt(p);
+                        if (limit != '>' && limit != ':') {
+                            classBound = referenceTypeSig();
+                        }
+                    }
+                    // If classBound is absent here, we start tokenizing
+                    // next type parameter, which can trigger failures
+                }
                 while (match(':')) {
                     if (interfaceBounds == null)
                         interfaceBounds = new ArrayList<>();

test/jdk/jdk/classfile/SignaturesTest.java

@@ -24,7 +24,7 @@
 /*
  * @test
  * @summary Testing Signatures.
- * @bug 8321540 8319463 8357955
+ * @bug 8321540 8319463 8357955 8368050 8368331
  * @run junit SignaturesTest
  */
 import java.io.IOException;
@@ -120,6 +120,20 @@ void testBuildingSignatures() {
         assertEqualsDeep(
                 ArrayTypeSig.of(2, TypeVarSig.of("E")),
                 Signature.parseFrom("[[TE;"));
+
+        assertEqualsDeep(
+                MethodSignature.of(
+                        List.of(TypeParam.of("A", ClassTypeSig.of("one/Two")), // /
+                                TypeParam.of("B", ClassTypeSig.of(ClassTypeSig.of("Outer"), "Inner")), // .
+                                TypeParam.of("C", ArrayTypeSig.of(BaseTypeSig.of('I'))), // [
+                                TypeParam.of("D", ClassTypeSig.of("Generic", TypeArg.unbounded())), // <
+                                TypeParam.of("E", TypeVarSig.of("A")), // ;
+                                TypeParam.of("F", (ClassTypeSig) null), // :
+                                TypeParam.of("G", (ClassTypeSig) null)), // >
+                        List.of(),
+                        BaseTypeSig.of('V')),
+                MethodSignature.parseFrom("<A:Lone/Two;B:LOuter.Inner;C:[ID:LGeneric<*>;E:TA;F:G:>()V")
+        );
     }
 
     @Test