intel-linux toolset detection broken

[Flamefire]

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Environment and version details

• Operating System+version: RHEL 7.5
• Compiler+version: icpc 19.1.2.254
• Shell: Bash
• B2 Version: 4.4-git

notice: found boost-build.jam at /tmp/boost_1_76_0/boost-build.jam
notice: loading B2 from /tmp/boost_1_76_0/tools/build/src/bootstrap.jam
notice: Searching '/etc' '/home/s3248973' '/tmp/boost_1_76_0/tools/build/src' '/tmp/boost_1_76_0/tools/build/src/kernel' '/tmp/boost_1_76_0/tools/build/src/util' '/tmp/boost_1_76_0/tools/build/src/build' '/tmp/boost_1_76_0/tools/build/src/tools' '/tmp/boost_1_76_0/tools/build/src/contrib' '/tmp/boost_1_76_0/tools/build/src/.' for site-config configuration file 'site-config.jam'.
notice: Configuration file 'site-config.jam' not found in '/etc' '/home/s3248973' '/tmp/boost_1_76_0/tools/build/src' '/tmp/boost_1_76_0/tools/build/src/kernel' '/tmp/boost_1_76_0/tools/build/src/util' '/tmp/boost_1_76_0/tools/build/src/build' '/tmp/boost_1_76_0/tools/build/src/tools' '/tmp/boost_1_76_0/tools/build/src/contrib' '/tmp/boost_1_76_0/tools/build/src/.'.
notice: Searching '/home/s3248973' '/tmp/boost_1_76_0/tools/build/src' '/tmp/boost_1_76_0/tools/build/src/kernel' '/tmp/boost_1_76_0/tools/build/src/util' '/tmp/boost_1_76_0/tools/build/src/build' '/tmp/boost_1_76_0/tools/build/src/tools' '/tmp/boost_1_76_0/tools/build/src/contrib' '/tmp/boost_1_76_0/tools/build/src/.' for user-config configuration file 'user-config.jam'.
notice: Configuration file 'user-config.jam' not found in '/home/s3248973' '/tmp/boost_1_76_0/tools/build/src' '/tmp/boost_1_76_0/tools/build/src/kernel' '/tmp/boost_1_76_0/tools/build/src/util' '/tmp/boost_1_76_0/tools/build/src/build' '/tmp/boost_1_76_0/tools/build/src/tools' '/tmp/boost_1_76_0/tools/build/src/contrib' '/tmp/boost_1_76_0/tools/build/src/.'.
notice: Searching '.' for project-config configuration file 'project-config.jam'.
notice: Loading project-config configuration file 'project-config.jam' from '.'.
notice: intel-linux command is icpc
notice: intel-linux version is 19.1.2.254
notice: will use 'icpc' for intel-linux, condition <toolset>intel-linux-19.1.2.254
notice: using intel libraries :: <toolset>intel-linux-19.1.2.254 :: /../lib/x86_64
notice: [zlib] Using pre-installed library
notice: [zlib] Condition
notice: [bzip2] Using pre-installed library
notice: [bzip2] Condition
notice: [lzma] Using pre-installed library
notice: [lzma] Condition
notice: [zstd] Using pre-installed library
notice: [zstd] Condition
notice: [python-cfg] Configuring python...

Brief problem description

Since 5ede4e8#diff-080a16b9c3fe0d92a5fc4bce7f4fe42dbdb2f33bac84510f8a50101ce81ed097 the intel-linux detection is broken making it impossible to use the intel compilers when installed in a non-standard location and relying on auto-detection via $PATH

Steps to reproduce the issue

• Set up $PATH, $CXX, $CC so that icpc is found
• ./bootstrap.sh --with-toolset=intel-linux
• ./b2 --debug-configuration

Actual behavior summary

What happens is that

b2/src/tools/intel-linux.jam

Line 100 in 5ede4e8

detected_command = [ common.find-tool icpc : $(bin_paths) : path-last ] ;

searches for icpc, finds it in $PATH but returns only the command, not the full path as per

b2/src/tools/common.jam

Line 343 in 5ede4e8

# If found in PATH, returns 'name' and if found in additional paths, returns

Furthermore the current behavior does not match the description where $PATH is searched for the intel tools:

b2/src/tools/intel.jam

Lines 22 to 23 in b4e1a65

	If compiler command is not specified, then B2 will look in PATH
	for an executable `icpc` (on Linux), or `icl.exe` (on Windows).

I find this quite worrying: Choosing the tool currently in $PATH should always be preferred over hard-coded guesses

When running b2 as above it will then fail to run properly seemingly using an empty string to invoke the compiler unless b2 is invoked with toolset=intel-linux explicitely.
Furthermore putting the full path to the compiler into project-config.jam will lead to an empty command_lib_path used at

b2/src/tools/intel-linux.jam

Lines 231 to 232 in 5ede4e8

	flags intel-linux.compile RUN_PATH $(condition) : $(command_lib_path) ;
	flags intel-linux.link RUN_PATH $(condition) : $(command_lib_path) ;

which I'm not sure is correct. It is also not enough to use the default toolset specified in project-config.cam by the bootstrap process