[mohitduhan19]

AddCustomContext moves key and value into std::map::emplace and then prints them in the duplicate-key warning. Two problems with that:

1. The message reports the wrong value. It prints the rejected value, not the one already stored:

   benchmark::AddCustomContext("foo", "bar");
   benchmark::AddCustomContext("foo", "qux");
   // before: Failed to add custom context "foo" as it already exists with value "qux"
   // after:  Failed to add custom context "foo" as it already exists with value "bar"

2. Use after move. Reading key/value after std::move relies on emplace leaving its arguments untouched when insertion fails, which the standard does not guarantee (an implementation may construct the node first). This is the bugprone-use-after-move finding in src/benchmark.cc from the clang-tidy list in [BUG] clang-tidy warnings and errors #1925. The moves were added in core(perf): use string move constructor for AddCustomContext #2005.

The fix reads the key and the existing value through the iterator returned by emplace, so it keeps the moves from #2005 and never touches the moved-from strings.

Testing

• AddCustomContext.DuplicateKey now captures stderr and checks the warning text. It fails on current main (prints "qux") and passes with this change.
• Full ctest: 88/88 pass with clang 18 and gcc (Linux).
• clang-format --dry-run --Werror clean on both files; clang-tidy no longer reports bugprone-use-after-move in src/benchmark.cc.

AI usage disclosure (per AGENTS.md)

I used Claude (Anthropic's AI assistant) to help find this clang-tidy finding, write the fix and the test, and run the test suite. I have reviewed the change and understand it, and I'm happy to discuss or revise it.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Gj2XnTKgWqWhmcDNH9gkv8

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[mohitduhan19]

Superseded by #2375 (same change, recreated so every commit author is covered by the CLA).