JDK14 spec query : MethodHandles:dropLookupMode(int)

[Mandy Chung]

On 3/9/20 10:45 AM, Chris Hegarty wrote:
> Sure, I guess it somewhat depends on how you see 8240242 [1] turning
> out. 8240242 clearly describes a similar(ish) issue where dropping
> PUBLIC, when it is not currently held, has no effect, i.e. it does not
> result in “no access” - this is either a bug in the implementation, or
> a bug/clarification in the spec. If the latter, then there are some
> scenarios where the outcome of passing a mode to dropLookupMode will
> have some dependency on the actual held modes.

The confusion here is the public lookup with UNCONDITIONAL mode.
In JDK 9, a public lookup has PUBLIC and UNCONDITIONAL modes set
whereas in 14 JDK-8226916 revises public lookup objects with
only UNCONDITIONAL bit set.

Here is the spec clarification I am thinking of that may explain why the 
focus is not whether MODULE bit is set or not.

@@ -1524,14 +1524,20 @@
           * Creates a lookup on the same lookup class which this lookup 
object
           * finds members, but with a lookup mode that has lost the 
given lookup mode.
           * The lookup mode to drop is one of {@link #PUBLIC PUBLIC}, 
{@link #MODULE
-         * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED 
PROTECTED} or {@link #PRIVATE PRIVATE}.
-         * {@link #PROTECTED PROTECTED} is always
-         * dropped and so the resulting lookup mode will never have 
this access capability.
-         * When dropping {@code PACKAGE} then the resulting lookup will 
not have {@code PACKAGE}
-         * or {@code PRIVATE} access. When dropping {@code MODULE} then 
the resulting lookup will
-         * not have {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} 
access. If {@code PUBLIC}
-         * is dropped then the resulting lookup has no access. If 
{@code UNCONDITIONAL}
-         * is dropped then the resulting lookup has no access.
+         * MODULE}, {@link #PACKAGE PACKAGE}, {@link #PROTECTED PROTECTED},
+         * {@link #PRIVATE PRIVATE}, or {@code UNCONDITIONAL}.
+         * If this lookup has at least {@code PUBLIC} mode then
+         * {@link #PROTECTED PROTECTED} is always dropped and so the 
resulting lookup
+         * mode will never have this access capability.  When dropping 
{@code PACKAGE}
+         * then the resulting lookup will not have {@code PACKAGE} or 
{@code PRIVATE} access.
+         * When dropping {@code MODULE} then the resulting lookup will 
not have
+         * {@code MODULE}, {@code PACKAGE}, or {@code PRIVATE} access.
+         * When dropping {@code PUBLIC} then the result lookup has no 
access.
+         *
+         * <p> If this lookup has {@code UNCONDITIONAL} mode, this 
lookup is a
+         * {@linkplain MethodHandles#publicLookup() public lookup} and 
it has no
+         * other mode set.  When dropping {@code UNCONDITIONAL} on a 
public lookup
+         * then the resulting lookup has has no access.
           *

Is this clearer?

Mandy