RFR: 8371309: Diagnostic.getEndPosition can throw an NPE with typical broken code [v2]

[Vicente Romero]

On Wed, 19 Nov 2025 09:02:05 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> When starting the compiler via API, a `DiagnosticListener` may be provided, to which all reported errors and warnings are reported.
>> 
>> The reported diagnostics are represented by `javax.tools.Diagnostic`, which has (among others) method `getEndPosition`, which requires the end-pos-table to be set in the `DiagnosticSource` object for the given file (see `AbstractLog.sourceMap`). But the end-pos-table is only set after the parse is done:
>> https://github.com/openjdk/jdk/blob/167c952bb0fefb5acc9782f4f4474d92097c93f8/src/jdk.compiler/share/classes/com/sun/tools/javac/main/JavaCompiler.java#L702
>> 
>> There are three problems with this:
>> - when a `Diagnostic` is reported by the parser, and the clients code calls `Diagnostic.getEndPosition`, the end-pos-table is not set yet, and the method crashes with an NPE
>> - the end-pos-table is never set for implicitly compiled (parsed) files:
>> https://github.com/openjdk/jdk/blob/167c952bb0fefb5acc9782f4f4474d92097c93f8/src/jdk.compiler/share/classes/com/sun/tools/javac/main/JavaCompiler.java#L840
>> - when a `Diagnostic` is reported for a tree by the parser, the tree on which the `Diagnostic` appear does not typically have the end position set yet - it is usually set only after the error/warning is reported
>> 
>> All those problems used to be hidden by this check:
>> https://github.com/openjdk/jdk/blob/6c48f4ed707bf0b15f9b6098de30db8aae6fa40f/src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeInfo.java#L649
>> but that has been removed:
>> https://github.com/openjdk/jdk/commit/c793de989facdb532021e1d5ddd01eb0e089b8e6
>> 
>> I have tried to fix this properly, by deferring the errors from the parser to a later point, properly setting the end-pos-table, and handling implicitly parsed files more correctly:
>> https://github.com/openjdk/jdk/compare/master...lahodaj:jdk:JDK-8371309b?expand=1
>> but this change is a bit involved, and potentially a bit dangerous.
>> 
>> So, for now, I propose to reinstate the null check in `TreeInfo.getEndPos`, to restore the JDK 25 behavior, and attempt to do the better solution later, hopefully earlier in the release cycle.
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Never return NOPOS from (JCTree-based) Diagnostic's start and end position.

looks good

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Marked as reviewed by vromero (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28316#pullrequestreview-3493077140