[llvm-bugs] [Bug 31409] New: Fail to link instantiation of basic_regex with a custom character type

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31409

            Bug ID: 31409
           Summary: Fail to link instantiation of basic_regex with a
                    custom character type
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: karen at codesynthesis.com
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com
    Classification: Unclassified

Trying to instantiate std::basic_regex template with a custom character type
results in a linker error like this:

driver.o:(.rodata._ZTVNSt3__123__match_any_but_newlineIN6build24test6script5regex9line_charEEE[_ZTVNSt3__123__match_any_but_newlineIN6build24test6script5regex9line_charEEE]+0x20):
undefined reference to
`std::__1::__match_any_but_newline<build2::test::script::regex::line_char>::__exec(std::__1::__state<build2::test::script::regex::line_char>&)
const'

That happens as libc++ only provides specialization of
__match_any_but_newline::__exec() for char and wchar_t types, and lacks
implementation which would be available for any other instantiation of the
__match_any_but_newline template.

Probably it would be right to assume that a custom character type can have no
notion of a newline character at all. As a real life example, in build2
toolchain we develop, such a character represents a line of a program output,
or an inner level regex matching such a line, or a syntax regex character.

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