[dejagnu] When the compilation result is normal, default_{target_compile,target_assemble,link} may return unexpected ANSI escape sequences.

[Fourish]

Description / Steps to reproduce the issue

When running the testsuite of gcc libstdc++ in windows, dejagnu reports an error

cd /PATH_TO_PACKAGE/src/build-UCRT
runtest --tool libstdc++ --srcdir=/PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite

Expected behavior

Running /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-abi/abi.exp ...
...
Running /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-dg/conformance.exp ...
...
Running /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-xmethods/xmethods.exp.
...

Actual behavior

Running /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-abi/abi.exp ...
ERROR: tcl error sourcing /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-abi/abi.exp.
ERROR: tcl error code NONE
ERROR: could not compile testsuite_abi.cc 
while executing
"error "could not compile $f"" 
(procedure "v3-build_support" line 63) 
invoked from within
"v3-build_support" 
(file "/PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-abi/abi.exp" line 34) 
invoked from within
"source /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-abi/abi.exp" 
("uplevel" body line 1) 
invoked from within
"uplevel #0 source /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-abi/abi.exp" 
invoked from within
"catch "uplevel #0 source $test_file_name" msg"
Running /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-dg/conformance.exp ...
ERROR: tcl error sourcing /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-dg/conformance.exp.
ERROR: tcl error code NONE
ERROR: could not compile testsuite_abi.cc
    while executing
"error "could not compile $f""
    (procedure "v3-build_support" line 63)
    invoked from within
"v3-build_support"
    (file "/PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-dg/conformance.exp" line 26)
    invoked from within
"source /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-dg/conformance.exp"
    ("uplevel" body line 1)
    invoked from within
"uplevel #0 source /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-dg/conformance.exp"
    invoked from within
"catch "uplevel #0 source $test_file_name" msg"
Running /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-prettyprinters/prettyprinters.exp ...
ERROR: tcl error sourcing /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-xmethods/xmethods.exp.
ERROR: tcl error code NONE
ERROR: could not compile testsuite_abi.cc
    while executing
"error "could not compile $f""
    (procedure "v3-build_support" line 63)
    invoked from within
"v3-build_support"
    (file "/PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-xmethods/xmethods.exp" line 26)
    invoked from within
"source /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-xmethods/xmethods.exp"
    ("uplevel" body line 1)
    invoked from within
"uplevel #0 source /PATH-TO-PACKAGE/src/gcc-15.2.0/libstdc++-v3/testsuite/libstdc++-xmethods/xmethods.exp"
    invoked from within
"catch "uplevel #0 source $test_file_name" msg"

Verification

• I have verified that my MSYS2 is up-to-date before submitting the report (see https://www.msys2.org/docs/updating/)

Windows Version

MINGW64_NT-10.0-26200

Are you willing to submit a PR?

yes

[Fourish]

This is likely because the v3-build_support function in /PATH-TO-GCC/libstdc++-v3/testsuite/lib/libstdc++.exp on line 800 returns the following error:

	if { [v3_target_compile $srcdir/util/$f $object_file "object" \
		  [list "incdir=$srcdir" "additional_flags=-w -fno-lto -fno-freestanding"]]
	     != "" } {
	    error "could not compile $f"
	}
...

v3_target_compile returns a non-empty string containing \033\[6n, making the boolean condition true.The return value of v3_target_compile comes from the default_target_compile function in /usr/share/dejagnu/target.exp. default_target_compile returns /033/[6n, causing all code that performs boolean checks on dependencies and "" to determine whether compilation was successful to throw an exception.
Adding a check before return $comp_output from default_target_compile, default_target_assemble, and default_link in /msys64/usr/share/dejagnu/target.exp

	binary scan $comp_output H* hex_content ;#jdbg
	;#jdbg puts "$hex_content" ;#jdbg
	if { $hex_content == "1b5b366e"} { ;#jdbg
	    set comp_output "" ;#jdbg
	} ;#jdbg

can alleviate this problem.