Allow license expressions in features

[autoantwort]

Fixes 2. of microsoft/vcpkg#31820 (comment)

[BillyONeal]

I would like to see an added test for what happens when it's bogus SPDX.

[autoantwort]

I would like to see an added test for what happens when it's bogus SPDX.

You mean like

vcpkg-tool/src/vcpkg-test/manifests.cpp

Lines 1173 to 1212 in 8c254a5

	TEST_CASE ("license error messages", "[manifests][license]")
	{
	ParseMessages messages;
	parse_spdx_license_expression("", messages);
	REQUIRE(messages.error);
	CHECK(messages.error->to_string() == R"(<license string>:1:1: error: SPDX license expression was empty.
	on expression:
	^)");
	parse_spdx_license_expression("MIT ()", messages);
	REQUIRE(messages.error);
	CHECK(messages.error->to_string() ==
	R"(<license string>:1:5: error: Expected a compound or the end of the string, found a parenthesis.
	on expression: MIT ()
	^)");
	parse_spdx_license_expression("MIT +", messages);
	REQUIRE(messages.error);
	CHECK(
	messages.error->to_string() ==
	R"(<license string>:1:5: error: SPDX license expression contains an extra '+'. These are only allowed directly after a license identifier.
	on expression: MIT +
	^)");
	parse_spdx_license_expression("MIT AND", messages);
	REQUIRE(messages.error);
	CHECK(messages.error->to_string() ==
	R"(<license string>:1:8: error: Expected a license name, found the end of the string.
	on expression: MIT AND
	^)");
	parse_spdx_license_expression("MIT AND unknownlicense", messages);
	CHECK(!messages.error);
	REQUIRE(messages.warnings.size() == 1);
	CHECK(
	test_format_parse_warning(messages.warnings[0]) ==
	R"(<license string>:1:9: warning: Unknown license identifier 'unknownlicense'. Known values are listed at https://spdx.org/licenses/
	on expression: MIT AND unknownlicense
	^)");
	}

I haven't duplicated the tests because the same deserializer was used

[BillyONeal]

I mean showing that parse_spdx_license_expression is correctly hooked up with any example, not the full blown mess that is every edge case there.

But this has waited long enough, thanks!

[vicroms]

We need to update the manifests reference documentation.

[autoantwort]

I have created MicrosoftDocs/vcpkg-docs#93