RFR: 8194743: Compiler implementation for Statements before super() [v4]

[Chen Liang]

On Wed, 17 May 2023 02:32:02 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:
> 
>   Use @enablePreview in tests in preference to explicit command line flags.

Quick question, since I don't know much about javac, I wonder what happens if you declare a local class or an anonymous class in the ctor prologue? Will that local/anonymous class have a mandated outer instance parameter in its constructor, and thus having access to a newly allocated but non-initialized object via `ClassName.this`?

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PR Comment: https://git.openjdk.org/jdk/pull/13656#issuecomment-1556500408