8361481: Flexible Constructor Bodies generates a compilation error when compiling a user supplied java.lang.Object class

[mcimadamore]

The JLS says:

IF a constructor body contains an explicit constructor invocation, the BlockStatements preceding the explicit constructor invocation are called the prologue of the constructor body."

Note the "IF". Only constructors that contain an explicit constructor invocation have a prologue.

But a constructor in Object doesn't contain an explicit constructor invocation:

If a constructor body does not begin with an explicit constructor invocation and the constructor being declared is not part of the primordial class Object, then the constructor body implicitly begins with a superclass constructor invocation "super();", an invocation of the constructor of its direct superclass that takes no arguments.

In other words, a constructor in the Object class has no prologue.

Unfortunately javac misses this, and sets the env.info.ctorPrologue at the start of all constructors (even those in Object). However, since no implicit super call is added to Object constructors, this flag remains set for the entire body of the Object constructor -- that is, it's as if the whole constructor body was one big prologue.

This results in spurious errors being generated (and referring to preview features), as demonstrated in the issue linked to this PR.

The fix is not to set the ctorPrologue flag if we're in a constructor of the Object class.

---

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Issue

• JDK-8361481: Flexible Constructor Bodies generates a compilation error when compiling a user supplied java.lang.Object class (Bug - P4)

Reviewers

• Jan Lahoda (@lahodaj - Reviewer) Review applies to 2bd99e00
• Vicente Romero (@vicente-romero-oracle - Reviewer)
• Chen Liang (@liach - Reviewer)

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@mcimadamore This change now passes all automated pre-integration checks.

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8361481: Flexible Constructor Bodies generates a compilation error when compiling a user supplied java.lang.Object class

Reviewed-by: vromero, liach, jlahoda

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At the time when this comment was updated there had been 19 new commits pushed to the master branch:

• 05c9eec: 8361214: An anonymous class is erroneously being classify as an abstract class
• fea73c1: 8360599: [TESTBUG] DumpThreadsWithEliminatedLock.java fails because of unstable inlining
• afb4a1b: 8354872: Clarify java.lang.Process resource cleanup
• ... and 16 more: https://git.openjdk.org/jdk/compare/5cf349c3b08324e994a4143dcc34a59fd81323f9...master

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[mlbridge]

Webrevs

• 01: Full - Incremental (4189ba17)
• 00: Full (2bd99e00)

[lahodaj]

Looks good to me.

[liach]

IMO the source 8 is redundant. A method call like toString in the ctor body should be sufficient.

[openjdk]

@mcimadamore Please do not rebase or force-push to an active PR as it invalidates existing review comments. Note for future reference, the bots always squash all changes into a single commit automatically as part of the integration. See OpenJDK Developers’ Guide for more information.

[vicente-romero-oracle]

lgtm

[liach]

The new test looks way better!

[mcimadamore]

/integrate

[openjdk]

Going to push as commit 1934bd8.
Since your change was applied there have been 28 commits pushed to the master branch:

• 7b255b8: 8361397: Rework CompileLog list synchronization
• 310ef85: 8305567: serviceability/tmtools/jstat/GcTest01.java failed utils.JstatGcResults.assertConsistency
• 5205eae: 8346753: Test javax/swing/JMenuItem/RightLeftOrientation/RightLeftOrientation.java fails on Windows Server 2025 x64 because the icons of RBMenuItem and CBMenuItem are not visible in Nimbus LookAndFeel
• ... and 25 more: https://git.openjdk.org/jdk/compare/5cf349c3b08324e994a4143dcc34a59fd81323f9...master

Your commit was automatically rebased without conflicts.

[openjdk]

@mcimadamore Pushed as commit 1934bd8.

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