False warning in C++ .hpp file about micro HOT 2 OPEN

Micro does not include a C++ compiler, the warning is coming from a linter or a language server you have set up. You should open the issue in their repository.

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I think @teodor256 did not "set up" anything. The issue is with micro's built-in linter plugin. It uses these commands for checking C or C++ files:

    makeLinter("gcc", "c", "gcc", {"-fsyntax-only", "-Wall", "-Wextra", "%f"}, "%f:%l:%c:.+: %m")
    makeLinter("g++", "c++", "gcc", {"-fsyntax-only","-std=c++14", "-Wall", "-Wextra", "%f"}, "%f:%l:%c:.+: %m")

So the problem is with gcc: it always throws #pragma once in main file if a file containing #pragma once is passed to the gcc command line, i.e. it assumes that header files should never be passed to it on the command line. Which is reasonable in normal case when compiling, but it also happens when gcc is run with -fsyntax-only. So gcc with -fsyntax-only cannot be quite reliably used for checking syntax of header files. And gcc doesn't even provide an explicit option to suppress this warning.

I see it is reported in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89808. See in particular comment https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89808#c11.

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