Firstly, my apologies. The test.cpp I supplied was an attempt at a quick simplification, and as you said it doesn't produce "enough" syntax errors actually.

I am pasting below a test.cpp that I have verified on my setup does hang the tramp window.

I'm afraid that there is another complication for reproducability. I cannot get the issue to reproduce when I do "M-x compile" then invoking "gcc test.cpp". It appears to reproduce only when doing "make" on a larger / more complex project containing test.cpp. This is true even when test.cpp is the first file that compiles in the project upon "make".

I attempted to make a small autotools project containing test.cpp, but even that doesn't seem to reproduce the tramp hang. Only by including test.cpp in a large preexisting project does the hang occur, at least for me.

I would suggest that you take a favorite large C++ autotools project, add test.cpp to the source tree and Makefile.am, and see if the hang reproduces for you.

For your reference, I am also pasting the output from the hung tramp window when I added test.cpp to a library within one of my own larger projects.

Regards,

D.

======= Hung Tramp Window ==========

-*- mode: compilation; default-directory: "/ssh:username@TWR1HM:/home/username/Dropbox/progs/thisprog/sbshared/src/" -*-
Compilation started at Sun Jan  3 11:02:36

make -k
make  all-am
make[1]: Entering directory '/home/username/Dropbox/progs/thisprog/sbshared/src'
/bin/bash ../libtool  --tag=CXX   --mode=compile g++ -DHAVE_CONFIG_H -I.    -std=c++11 -Wall -Werror -Wclobbered -Wempty-body -Wignored-qualifiers -Wmissing-field-initializers -Wsign-compare -Wtype-limits -Wuninitialized -Winit-self -Wcast-align -Wfloat-equal -Wformat=2 -Wno-psabi  -I/usr/include/libxml2 -I../../../kilo  -I../../../rapidxml  -g3 -Og -DDEBUG=1 -MT test.lo -MD -MP -MF .deps/test.Tpo -c -o test.lo test.cpp
libtool: compile:  g++ -DHAVE_CONFIG_H -I. -std=c++11 -Wall -Werror -Wclobbered -Wempty-body -Wignored-qualifiers -Wmissing-field-initializers -Wsign-compare -Wtype-limits -Wuninitialized -Winit-self -Wcast-align -Wfloat-equal -Wformat=2 -Wno-psabi -I/usr/include/libxml2 -I../../../kilo -I../../../rapidxml -g3 -Og -DDEBUG=1 -MT test.lo -MD -MP -MF .deps/test.Tpo -c test.cpp  -fPIC -DPIC -o .libs/test.o

==================================

// test.cpp - for lots of syntax errors

#include <mutex>
#include <string>
#include <vector>
#include <memory>        
 
class A1
{
    int f1();
    int f2();
    int f3();
    int f4();
    int f5();
    int f6();
    int f7();
    int f8();
    int f9();
};

class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
class Nested
{
    A1 m1;
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};
};


class A2
{
    std::shared_ptr<A1> a1ptr;
    A2() {A1 a1; a1ptr = &a1;}
};

#define AN_BODY                                                    \
    A1 x1;                                                         \
    A1 x2;                                                         \
    std::string s1(x1);                                            \
    std::string s2(x2);                                            \
Nested n1;                                                              \
const std::vector<std::string> v1(1, a1);                               \
const std::vector<std::string> v1(1, n1);                               \
std::vector<std::string> * v1_cptr(&v1);                                \
return(s1+s2);

int A1::f1()
{
    AN_BODY;
}

int A1::f2()
{
    AN_BODY;
}

int A1::f3()
{
    AN_BODY;
}

int A1::f4()
{
    AN_BODY;
}

int A1::f5()
{
    AN_BODY;
}

int A1::f6()
{
    AN_BODY;
}

int A1::f7()
{
    AN_BODY;
}

int A1::f8()
{
    AN_BODY;
}

int A1::f9()
{
    AN_BODY;
}

int A1::f10()
{
    AN_BODY;
}


int main(int argc, char* argv[])
{
    AN_BODY;
}
// end test.cpp

==================================

On Sun, Jan 3, 2021 at 2:27 AM Michael Albinus <michael.albinus@gmx.de> wrote: