[cling] Clang is conditionally invoked with the wrong driver mode depending on the executable's name

[silverweed]

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Description

(see also llvm/llvm-project#225385 for the original report)

When ROOT is initialized it also initializes Cling, a complex process that involves invoking Clang with some predefined set of flags. When Clang is invoked this way, the ClangExecutable argument (used in Driver::BuildCompilation, which is where this bug likely originates) is not set to clang but to the name of the executable that is initializing ROOT.

One can easily reproduce this behavior by compiling this ROOT code:

// compile with: c++ -o cl thisfile.cpp $(root-config --cflags --libs) (you need to source thisroot.sh)
#include <TROOT.h>
int main() {
// this causes ROOT to be initialized
gROOT;
}

and name the resulting binary cl (or anything containing cl- or ending with cl). In this case, the errors will come from Cling, in a form similar to this:

warning: unknown argument ignored in clang-cl: '-fcxx-modules'
warning: unknown argument ignored in clang-cl: '-fmodules-cache-path=/home/user/root_build/debug/lib'
warning: unknown argument ignored in clang-cl: '-std=c++17'
warning: unknown argument ignored in clang-cl: '-fsigned-char'
warning: unknown argument ignored in clang-cl: '-fsized-deallocation'
warning: unknown argument ignored in clang-cl: '-fmodules-cache-path=/home/user/root_build/debug/lib'
warning: unknown argument ignored in clang-cl: '-fno-implicit-module-maps'
warning: unknown argument ignored in clang-cl: '-Rmodule-build'
warning: unknown argument ignored in clang-cl: '-fno-autolink'
warning: unknown argument ignored in clang-cl: '-cxx-isystem'
warning: unknown argument ignored in clang-cl: '-cxx-isystem'
warning: unknown argument ignored in clang-cl: '-cxx-isystem'
warning: unknown argument ignored in clang-cl: '-nostdinc++'
warning: unable to find a Visual Studio installation; try running Clang from a developer command prompt
cl: /home/user/root/interpreter/cling/lib/Interpreter/CIFactory.cpp:1025: bool (anonymous namespace)::SetupCompiler(CompilerInstance *, const CompilerOptions &, bool, bool): Assertion `LangOpts.CPlusPlus17 && "Language version mismatch"' failed.
fish: Job 1, './cl' terminated by signal SIGABRT (Abort)

Reproducer

Create a C++ file containing

#include <TROOT.h>
int main() { gROOT; }

Compile it to a binary named foocl and run it.

ROOT version

master

Installation method

any

Operating system

any

Additional context

No response