ParserEngine.h should include expat.h "quoted" not <angle bracketed>

[Vadrgh]

Summary

When using poco as a conan2 managed dependency of a cmake project, including Poco/SAX/SAXParser.h results in Poco/XML/ParserEngine.h:22:10: error: 'expat.h' file not found.

With clang instead of g++ there is an additional hint:

 'expat.h' file not found with <angled> include; use "quotes" instead

After following that suggestion and patching ParserEngine.h in the conan repository / local cache, the project compiles.

Details

Dev Environment

• OS: Fedora38
• Tools:
  • gcc: 13.1.1
  • clang: 16.0.4
  • cmake: 3.26.4
  • conan: 2.0.6
• dependency specified as poco/1.12.4

Observations

The relevant part in HEAD of ParserEngine.h reads

#if defined(POCO_UNBUNDLED)
#include <expat.h>
#else
#include "Poco/XML/expat.h"

⇒ only for POCO_UNBUNDLED expat.h is a system(-override) include.

Maybe more important: same poco/1.12.4 worked before on Fedora36 with conan-1.58 and the toolchain belonging to that OS version,- whatever that was.

[obiltschnig]

It's not as simple to solve. Ideally, Conan should set the system include path in the correct way. A change would break things for everyone else.