JDK-8266670 : Better modeling of access flags in core reflection
  • Type: Enhancement
  • Component: core-libs
  • Sub-Component: java.lang:reflect
  • Affected Version: 17
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2021-05-06
  • Updated: 2022-12-13
  • Resolved: 2022-06-25
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JDK 20
20 b04Fixed
Related Reports
CSR :  
JDK-8281660 - Better modeling of access flags in core reflection
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JDK-8289106 - Add model of class file versions to core reflection
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JDK-8286101 - Support formatting in @value tag
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JDK-8291360 - Create entry points to expose low-level class file information
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JDK-8291734 - Return accurate ACC_SUPER access flag for classes
Relates :  
JDK-8292576 - Improve wording of AccessFlag-related specs
Relates :  
JDK-8266524 - javac changes for JEP 306
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JDK-8296950 - [lworld] AccessFlags should be specific to class file version
Relates :  
JDK-8297271 - AccessFlags should be specific to class file version
Relates :  
JDK-6354476 - (reflect) {Method, Constructor}.toString prints out inappropriate modifiers
Relates :  
JDK-8145048 - consider enhancements to EnumMap and EnumSet
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JDK-8287330 - (valhalla) Better modeling of access flags in core reflection
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JDK-8281766 - Update java.lang.reflect.Parameter to implement Member
Description
Modifiers in core reflection and currently modeling using bit positions in an integer by java.lang.reflect.Modifier. This simple model does not fully capture existing nuances of modifiers. For example, there are collisions between the modifier bit positions for concepts used for fields, method, and types. These uses need to be disambiguated in for textual representations (JDK-6354476) and elsewhere.

With the possibility of a bit position being reused in the same kind of construct for different purposes on different class file versions (JDK-8266524), a more capable model of core reflection modifiers will be needed.

As a straw man proposal:
- core reflection classes get a new "modifiers" method which returns an enum set of modifiers
- the modifiers enum has a constant for each modifier. A modifier can include information such as its bit position, what kinds of constructs it is applicable to (classes, fields, methods, etc.), string representation, etc.

This would allow bit positions with collisions, such as var-args and transient, to be modeled appropriately.

Such a class would be analogous to javax.lang.model.element.Modifier.
Comments
Changeset: de746714 Author: Joe Darcy <darcy@openjdk.org> Date: 2022-06-25 19:09:43 +0000 URL: https://git.openjdk.org/jdk/commit/de7467146fc3759110299e8297628db2b0b16800
25-06-2022
Note the ACC_SUPER bit is apparently stripped from Class.getModifers in the JVM (JDK-4109635) and test: jdk/java/lang/Class/getModifiers/StripACC_SUPER.java
16-06-2022
A pull request was submitted for review. URL: https://git.openjdk.java.net/jdk/pull/7445 Date: 2022-02-11 18:31:57 +0000
11-02-2022
Proof of concept version of enum: --- /dev/null +++ b/src/java.base/share/classes/java/lang/reflect/ModifierFlag.java @@ -0,0 +1,248 @@ +package java.lang.reflect; + +import java.lang.annotation.ElementType; +import java.util.Set; +import static java.lang.annotation.ElementType.*; + +/** + * tl;dr -- JVM modifier flag. Related to but different than + * java.lang.Modifier + * + * The values for the constants + * representing the modifiers are taken from the tables in sections + * {@jvms 4.1}, {@jvms 4.4}, {@jvms 4.5}, and {@jvms 4.7} of + * <cite>The Java Virtual Machine Specification</cite>. + * + * @jls 8.1.1 Class Modifiers + * @jls 8.3.1 Field Modifiers + * @jls 8.4.3 Method Modifiers + * @jls 8.8.3 Constructor Modifiers + * @jls 9.1.1 Interface Modifiers + * @see java.lang.reflect.Modifier + * @see javax.lang.model.element.Modifier + */ +public enum ModifierFlag { + /** + * The flag {@code public}/{@code ACC_PUBLIC}. + */ + PUBLIC(Modifier.PUBLIC, true, Set.of(TYPE, CONSTRUCTOR, METHOD, FIELD)), + + /** + * The flag {@code protected}/{@code ACC_PROTECTED}. + */ + PROTECTED(Modifier.PROTECTED, true, Set.of(CONSTRUCTOR, METHOD, FIELD)), + + /** + * The flag {@code private}/{@code ACC_PRIVATE}. + */ + PRIVATE(Modifier.PRIVATE, true, Set.of(CONSTRUCTOR, METHOD, FIELD)), + + /** + * The flag {@code abstract}/{@code ACC_ABSTRACT}. + */ + ABSTRACT(Modifier.ABSTRACT, true, Set.of(TYPE, METHOD)), + +// /** +// * The flag {@code default}. +// */ +// DEFAULT, + + /** + * The flag {@code static}/{@code ACC_STATIC}. + */ + STATIC(Modifier.STATIC, true, Set.of(FIELD, METHOD)), + +// /** +// * The flag {@code sealed} +// * @since 15 +// */ +// SEALED, + +// /** +// * The flag {@code non-sealed} +// * @since 15 +// */ +// NON_SEALED { +// public String toString() { +// return "non-sealed"; +// } +// }, + + /** + * The flag {@code final}/{@code ACC_FINAL}. + */ + FINAL(Modifier.FINAL, true, Set.of(FIELD, METHOD, PARAMETER, TYPE)), + + /** + * The flag {@code transient}/{@code ACC_TRANSIENT}. + */ + TRANSIENT(Modifier.TRANSIENT, true, Set.of(FIELD)), + + /** + * The flag {@code volatile}/{@code ACC_VOLATILE}. + */ + VOLATILE(Modifier.VOLATILE, true, Set.of(FIELD)), + + /** + * The flag {@code synchronized}/{@code ACC_SYNCHRONIZED}. + */ + SYNCHRONIZED(Modifier.SYNCHRONIZED, true, Set.of(METHOD, CONSTRUCTOR)), + + /** + * The flag {@code native}/{@code ACC_NATIVE}. + */ + NATIVE(Modifier.NATIVE, true, Set.of(METHOD)), + + /** + * The {@code ACC_INTERFACE} flag. + */ + INTERFACE(Modifier.INTERFACE, false, Set.of(TYPE)), + + /** + * The flag {@code strictfp}/{@code ACC_STRICT}. + */ + STRICT(Modifier.STRICT, true, Set.of(METHOD, CONSTRUCTOR)), + + /** + * The flag {@code ACC_BRIDGE} + */ + BRIDGE(0x00000040, false, Set.of(METHOD, CONSTRUCTOR)), + + /** + * The flag {@code ACC_VARARGS}. + */ + VARARGS(0x00000080, false, Set.of(METHOD, CONSTRUCTOR)), + + /** + * The flag {@code ACC_SYNTHETIC}. + */ + SYNTHETIC(0x00001000, false, Set.of(TYPE, FIELD, METHOD, CONSTRUCTOR, ElementType.MODULE, PARAMETER)), + + /** + * The flag {@code ACC_MANDATED}. + */ + MANDATED(0x00008000, false, Set.of(ElementType.MODULE, PARAMETER)), + + /** + * The flag {@code ACC_ANNOTATION}. + */ + ANNOTATION(0x00002000, false, Set.of(TYPE)), + + /** + * The flag {@code ACC_ENUM}. + */ + ENUM(0x00004000, false, Set.of(TYPE, FIELD)), + + /** + * The flag {@code ACC_MODULE}. + */ + MODULE(0x8000, false, Set.of(TYPE)) + ; + +// /** +// * The Java source modifiers that can be applied to a class. +// * @jls 8.1.1 Class Modifiers +// */ +// private static final int CLASS_MODIFIERS = +// Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE | +// Modifier.ABSTRACT | Modifier.STATIC | Modifier.FINAL | +// Modifier.STRICT; + +// /** +// * The Java source modifiers that can be applied to an interface. +// * @jls 9.1.1 Interface Modifiers +// */ +// private static final int INTERFACE_MODIFIERS = +// Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE | +// Modifier.ABSTRACT | Modifier.STATIC | Modifier.STRICT; + + +// /** +// * The Java source modifiers that can be applied to a constructor. +// * @jls 8.8.3 Constructor Modifiers +// */ +// private static final int CONSTRUCTOR_MODIFIERS = +// Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE; + +// /** +// * The Java source modifiers that can be applied to a method. +// * @jls 8.4.3 Method Modifiers +// */ +// private static final int METHOD_MODIFIERS = +// Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE | +// Modifier.ABSTRACT | Modifier.STATIC | Modifier.FINAL | +// Modifier.SYNCHRONIZED | Modifier.NATIVE | Modifier.STRICT; + +// /** +// * The Java source modifiers that can be applied to a field. +// * @jls 8.3.1 Field Modifiers +// */ +// private static final int FIELD_MODIFIERS = +// Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE | +// Modifier.STATIC | Modifier.FINAL | Modifier.TRANSIENT | +// Modifier.VOLATILE; + +// /** +// * The Java source modifiers that can be applied to a method or constructor parameter. +// * @jls 8.4.1 Formal Parameters +// */ +// private static final int PARAMETER_MODIFIERS = +// Modifier.FINAL; + +// static final int ACCESS_MODIFIERS = +// Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE; + + + private int mask; + private boolean sourceModifier; + + // For now, reuse ElementType rather than defining a separate type. + private Set<ElementType> targets; + + private ModifierFlag(Set<ElementType> targets) { + this.mask = 0x0; + this.sourceModifier = false; + this.targets = targets; + } + + private ModifierFlag(int mask, boolean sourceModifier, Set<ElementType> targets) { + this.mask = mask; + this.sourceModifier = sourceModifier; + this.targets = targets; + } + + /** + * {@return corresponding integer mask for the flag; 0 if none} + */ + public int mask() { + return mask; + } + + /** + * {@return whether or not the flag has a directly corresponding + * modifier in the Java programming language} + */ + public boolean sourceModifer() { + return sourceModifier; + } + + /** + * {@return kinds of constructs the flag can be applied to} + */ + public Set<ElementType> targets() { + return targets; + } + + /** + * Returns this modifier's name as defined in <cite>The + * Java Language Specification</cite>. + * The flag name is the {@linkplain #name() name of the enum + * constant} in lowercase and with any underscores ("{@code _}") + * replaced with hyphens ("{@code -}"). + * @return the modifier's name + */ + @Override + public String toString() { + return name().toLowerCase(java.util.Locale.US); + } +}
14-05-2021
One of the defects with the existing modeling of modifiers is that each of the reflective entities (class, method, field, etc) yield their modifiers as an int, but modifiers have become dependent on multiple dimensions of context: what kind of entity does the modifier appear on, and the classfile version. By defining the modifiers abstractly (as an enum) and then letting the reflective entities yield up a set of modifiers, we can guarantee the returned modifiers are consistent with the kind and classfile version of the reflective entity. Further, there have been many bugs regarding the `toString` methods of various reflective entities for this reason; these could be made to go away by centralizing the interpretation of the ACC bits with the proper context.
07-05-2021