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

[Vicente Romero]

On Fri, 14 Nov 2025 08:22:46 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.

looks good

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Marked as reviewed by vromero (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28316#pullrequestreview-3467020088