RFR: 8194743: Compiler implementation for Statements before super() [v16]

Maurizio Cimadamore mcimadamore at openjdk.org
Mon Sep 25 17:07:17 UTC 2023

On Mon, 25 Sep 2023 16:04:09 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

>> This is a first draft of a patch for JEP 447.
>> Summary of changes:
>> 1. Track when we're within a constructor "prologue" via new flag `AttrContext.ctorPrologue`
>> 1. Add checks for illegal early access to `this` in constructor prologues, and update existing checks to distinguish between static context vs. constructor prologue context
>> 1. Verify allowed placement of `super()`/`this()` calls via new method `Check.checkSuperInitCalls()`
>> 1. Remove/refactor assumptions in several places that `super()`/`this()` was always the first statement
>> The changes in `Flow.java` are an example of <span>#</span>4. `Flow.FlowAnalyzer` checks for uncaught checked exceptions. For initializer blocks, this was previously done by requiring that any checked exceptions thrown be declared as thrown by all constructors containing `super()`. This list of checked exceptions was being pre-calculated before recursing into the initial constructors. This worked because initializer blocks were executed at the beginning of each initial constructor right after `super()` is called.
>> Now initializer blocks are traversed as each `super()` invocation is encountered, reflecting what actually happens at runtime. Similarly, final fields are marked as DA after encountering `this()`, not automatically at the beginning of those  constructors. These changes produce equivalent checks, but are compatible with the new flexibility of placement of `super()`/`this()` as well as possible future changes that could occur along these same lines.
> Archie Cobbs has updated the pull request incrementally with one additional commit since the last revision:
>   Have RefBeforeCtorCalledError extend StaticError and customize debug strings.

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java line 1511:

> 1509:                     if (staticOnly)
> 1510:                         return new StaticError(sym);
> 1511:                     if (env1.info.ctorPrologue && (sym.flags_field & SYNTHETIC) == 0)

where does the SYNTHETIC check comes from?

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Resolve.java line 2016:

> 2014:                         if (staticOnly)
> 2015:                             return new StaticError(sym);
> 2016:                         if (env1.info.ctorPrologue && env1 == env)

where does `env1 == env` come from?


PR Review Comment: https://git.openjdk.org/jdk/pull/13656#discussion_r1336170440
PR Review Comment: https://git.openjdk.org/jdk/pull/13656#discussion_r1336170745

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