Fix crash for diagnostics around source with embedded nulls

[damyanp]

Previously if the source contained embedded nulls and a diagnostic range included that this would result in an assert firing (and then a crash in builds without asserts).

This change makes it quietly return in this case, and adds a regression test for this situation.

[Copilot]

Pull request overview

Fixes a crash in DXC’s diagnostic range highlighting when the input source contains embedded null bytes, by making the highlighter bail out instead of asserting/crashing, and adds a regression test to cover the scenario.

Changes:

• Update highlightRange() to return early when trimming whitespace causes the start/end columns to cross (e.g., due to embedded null bytes).
• Add a new DXC lit test that feeds an HLSL source containing an embedded \x00 and verifies an expected diagnostic instead of a crash.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
tools/clang/lib/Frontend/TextDiagnostic.cpp	Avoids crashing/asserting when a token highlight range becomes invalid after whitespace trimming.
tools/clang/test/DXC/highlight-range-null-byte.test	Regression test ensuring embedded null bytes don’t crash diagnostics/highlighting.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.