Enable colors when compiling foreign stubs.

[MisterDA]

Hi!
I’m compiling C++ foreign stubs, and there are errors in it. I noticed that the G++ output doesn’t have colors, so I added the -fdiagnostics-color=always of G++ flag in the dune configuration. However, ansi escape codes are not interpreted and are outputted raw (the output is also messed up):

required fro;01;K
error: static assertion failed: co;01;31;Kis_invocable_v<const _Compare&, const _Key&, const _Key&>

I’d suggest to find a work-around to let processes in foreign stubs output ansi escape code that are correctly interpreted by the terminal, especially when using the --verbose option of Dune.

[ghost]

Dune is parsing the ansi sequences in the output of commands and re-printing them. In this case it seems that it doesn't understand the output of G++. Can you pipe the output of G++ into hexdump -C and report the result here? I'd like to see what the ansi sequences G++ produces look like.

[MisterDA]

Sorry, I should have added means to reproduce the bug. In this particular case, I get a compilation error when enabling C++17. Theses are the steps I took, but one could craft a smaller example.
Using dune version 2.4.0, g++ version (Arch Linux 9.3.0-1) 9.3.0

git clone git@github.com:AltGr/ocaml-mccs.git
cd ocaml-mccs
git checkout 93cd3b25878c1a2bde5cab0a5c85a376936dc183

patch -p1 << EOF
diff --git a/src/dune b/src/dune
index dde1111..b495213 100644
--- a/src/dune
+++ b/src/dune
@@ -9,6 +9,7 @@
   :standard
   -I
   .
+  -std=c++17
   (:include cxxflags.sexp))
  (c_library_flags
   :standard
EOF
dune build	# output is correct, but uncoloured

patch -p1 << EOF
diff --git a/src/dune b/src/dune
index b495213..ff4c528 100644
--- a/src/dune
+++ b/src/dune
@@ -10,6 +10,7 @@
   -I
   .
   -std=c++17
+  -fdiagnostics-color=always
   (:include cxxflags.sexp))
  (c_library_flags
   :standard
EOF
dune build	# output is not correct, and uncoloured

dune build 2>&1 | hexdump -C

I have the feeling that the two last outputs differ, maybe it has something to do with the piping?

[ghost]

Piping the output of dune won't tell us much, we need to capture the output of G++ directly if we want to see what it sends to stdout. What you can do is look in _build/log the exact g++ command emitted by dune, copy&paste this command in your terminal, add the relevant argument and pipe its output.

[MisterDA]

Ran into this issue again, and you were right, GCC emits a special ANSI code that Dune does not seem to understand. clang doesn't emit this code.

From https://invisible-island.net/xterm/ctlseqs/ctlseqs.html#h2-VT52-Mode:

ESC K Erase from the cursor to the end of the line.

$ echo '#warning "this is a warning"' > warning.c
$ gcc -fdiagnostics-color=always -c warning.c -o warning.o 2>&1 | hexdump -C 
00000000  1b 5b 30 31 6d 1b 5b 4b  77 61 72 6e 69 6e 67 2e  |.[01m.[Kwarning.|
00000010  63 3a 31 3a 32 3a 1b 5b  6d 1b 5b 4b 20 1b 5b 30  |c:1:2:.[m.[K .[0|
00000020  31 3b 33 35 6d 1b 5b 4b  61 74 74 65 6e 74 69 6f  |1;35m.[Kattentio|
00000030  6e 3a 20 1b 5b 6d 1b 5b  4b 23 77 61 72 6e 69 6e  |n: .[m.[K#warnin|
00000040  67 20 22 74 68 69 73 20  69 73 20 61 20 77 61 72  |g "this is a war|
00000050  6e 69 6e 67 22 20 5b 1b  5b 30 31 3b 33 35 6d 1b  |ning" [.[01;35m.|
00000060  5b 4b 2d 57 63 70 70 1b  5b 6d 1b 5b 4b 5d 0a 20  |[K-Wcpp.[m.[K]. |
00000070  20 20 20 31 20 7c 20 23  1b 5b 30 31 3b 33 35 6d  |   1 | #.[01;35m|
00000080  1b 5b 4b 77 61 72 6e 69  6e 67 1b 5b 6d 1b 5b 4b  |.[Kwarning.[m.[K|
00000090  20 22 74 68 69 73 20 69  73 20 61 20 77 61 72 6e  | "this is a warn|
000000a0  69 6e 67 22 0a 20 20 20  20 20 20 7c 20 20 1b 5b  |ing".      |  .[|
000000b0  30 31 3b 33 35 6d 1b 5b  4b 5e 7e 7e 7e 7e 7e 7e  |01;35m.[K^~~~~~~|
000000c0  1b 5b 6d 1b 5b 4b 0a                              |.[m.[K.|
000000c7

[MisterDA]

The issue with the K escape code was fixed in #6214 and colors support for C/C++ stubs was added in #4083.