Add support for C23/GNU C23 standard flags

[Copilot]

parseCStandard incorrectly grouped C23 flags (c23, gnu23, c2x, gnu2x, iso9899:2024) with C17 flags in a single regex, mapping them all to c17/gnu17. This caused "Unknown C standard control flag: c23" and Standard: undefined in IntelliSense configuration.

The prior fix in #763 added C++23/C++26 support but missed the C standard side.

Changes

• src/parser.ts — Split the combined C17/C23 regex into two distinct branches:

  - } else if (/(c|gnu)(17|18|23|2x|iso9899:(2017|2018|2024))/.test(std)) {
  -   // everything maps to c17
  + } else if (/(c|gnu)(17|18|iso9899:(2017|2018))/.test(std)) {
  +   // c17/c18 → c17
  + } else if (/(c|gnu)(23|2x|iso9899:2024)/.test(std)) {
  +   // c23/c2x → c23

• src/util.ts — Add "c23" and "gnu23" to StandardVersion type
• src/test/fakeSuite/extension.test.ts — Add test suite for C standard parsing (C23, C17, older)
• CHANGELOG.md — Add entry for [Bug] Unknown C standard control flag: c23 #803

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• 0psvsblobprodwus2145.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)
• 8wdvsblobprodwus2137.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)
• b15vsblobprodwus2164.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/_temp/ghcca-node/node/bin/npm install (dns block)
• b53vsblobprodwus2154.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)
• isovsblobprodwus211.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)
• lusvsblobprodwus2166.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/_temp/ghcca-node/node/bin/npm install (dns block)
• pkwvsblobprodwus2126.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/_temp/ghcca-node/node/bin/npm install (dns block)
• v41vsblobprodwus2175.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)
• vd2vsblobprodwus2150.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)
• vjmvsblobprodwus2182.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/_temp/ghcca-node/node/bin/npm install (dns block)
• vm9vsblobprodwus2190.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /home/REDACTED/work/_temp/ghcca-node/node/bin/npm install (dns block)
• wlnvsblobprodwus2188.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)
• y1rvsblobprodwus2136.vsblob.vsassets.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install (dns block)
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node node /usr/local/bin/yarn install --registry REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

[snehara99]

validated locally