[GROOVY-7656] Spread safe method calls on list literals result in the list expression being evaluated twice (SC)

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 2.4.5
• Fix Version/s: 2.4.6
• Component/s: Static compilation
• Assignee: Shil Sinha
• Reporter: Shil Sinha
• Created: 02/Nov/15 15:48
• Updated: 22/Feb/16 20:48
• Resolved: 15/Nov/15 08:18

Description

When a list literal is the receiver for a statically compiled spread safe method call expression, the instructions to create the list are included twice. Example:

@groovy.transform.CompileStatic
void test() {
    ['a']*.size()
}

The bytecode for the method above is:

 L0
    LINENUMBER 3 L0
    NEW java/util/ArrayList
    DUP
    INVOKESPECIAL java/util/ArrayList.<init> ()V
    ASTORE 1
   L1
    ALOAD 1
    POP
    ICONST_1
    ANEWARRAY java/lang/Object
    DUP
    ICONST_0
    LDC "a"
    AASTORE
    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.createList ([Ljava/lang/Object;)Ljava/util/List;
    IFNULL L2
    ACONST_NULL
    ASTORE 2
   L3
    ICONST_1
    ANEWARRAY java/lang/Object
    DUP
    ICONST_0
    LDC "a"
    AASTORE
    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.createList ([Ljava/lang/Object;)Ljava/util/List;
    INVOKEINTERFACE java/util/List.iterator ()Ljava/util/Iterator;
    ASTORE 3
   L4
    ALOAD 3
    INVOKEINTERFACE java/util/Iterator.hasNext ()Z
    IFEQ L2
    ALOAD 3
    INVOKEINTERFACE java/util/Iterator.next ()Ljava/lang/Object;
    ASTORE 2
    ALOAD 1
    ALOAD 2
    DUP
    ASTORE 4
    IFNULL L5
    ALOAD 4
    INVOKESTATIC org/codehaus/groovy/runtime/typehandling/ShortTypeHandling.castToString (Ljava/lang/Object;)Ljava/lang/String;
    CHECKCAST java/lang/String
    INVOKESTATIC org/codehaus/groovy/runtime/StringGroovyMethods.size (Ljava/lang/String;)I
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    GOTO L6
   L5
    ACONST_NULL
   L6
    INVOKEVIRTUAL java/util/ArrayList.add (Ljava/lang/Object;)Z
    POP
    GOTO L4
   L2
    ALOAD 1
    POP

If the list expression contains method calls that have side effects, this can cause serious problems. The example below is trivial, but shows the general case:

@groovy.transform.CompileStatic
void test() {
    def list = ['abc']
    def lengths = [list.removeAt(0)]*.length() // throws IndexOutOfBoundsException
}