[llvm-bugs] [Bug 47252] New: clang-scan-deps doesn't change directory to compilation database "directory" folder

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47252

            Bug ID: 47252
           Summary: clang-scan-deps doesn't change directory to
                    compilation database "directory" folder
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Tooling
          Assignee: unassignedclangbugs at nondot.org
          Reporter: romain.geissler at amadeus.com
                CC: llvm-bugs at lists.llvm.org

Hi,

I meet a problem when using a clang-scan-deps with a compilation database
generated with a given current working directory, but then later
clang-scan-deps is run with another different working directory.

Full example:

> cat include/A.h
#ifndef _A_h_
#define _A_h_

class A
{
    public:
        void f();
};

#endif

> cat src/A.cpp
#include "A.h"

void A::f() {}

> cat Makefile
all:src/A.o compile_commands.json run_scan_deps

src/%.o:src/%.cpp
        clang -MJ $<.d.json -I include -o $@ -c $<

compile_commands.json:src/A.cpp.d.json src/A.o
        sed -e '1i[' -e '$$s/,$$//' -e '$$a]' src/*.d.json > $@

run_scan_deps:compile_commands.json
        cat $<
        clang-scan-deps --compilation-database=$<
        (cd src && clang-scan-deps --compilation-database=../$<)

clean:  
        ${RM} src/*.o src/*.d.json compile_commands.json

.PHONY:all clean run_scan_deps


And if I run this:

> make
clang -MJ src/A.cpp.d.json -I include -o src/A.o -c src/A.cpp
sed -e '1i[' -e '$s/,$//' -e '$a]' src/*.d.json > compile_commands.json
cat compile_commands.json
[
{ "directory": "/remote/users/rgeissler/wk/tmp/clang-scan-deps", "file":
"src/A.cpp", "output": "src/A.o", "arguments":
["/remote/tools/Linux/2.6/1A/toolchain/x86_64-v21.0.4/bin/clang-12", "-xc++",
"src/A.cpp", "-I", "include", "-o", "src/A.o", "-c",
"--target=x86_64-1a-linux-gnu"]}                                                
]

# First invocation of clang-scan-deps with the same current working directory
works:
clang-scan-deps --compilation-database=compile_commands.json
src/A.o: /remote/users/rgeissler/wk/tmp/clang-scan-deps/src/A.cpp \
  /remote/users/rgeissler/wk/tmp/clang-scan-deps/include/A.h


# While if I change directory, it doesn't work anymore
(cd src && clang-scan-deps --compilation-database=../compile_commands.json)
Error while scanning dependencies for src/A.cpp:
error: no such file or directory: 'src/A.cpp'
error: no input files 
error: unable to handle compilation, expected exactly one compiler job in ''
Makefile:12: recipe for target 'run_scan_deps' failed
make: *** [run_scan_deps] Error 1

I would have hoped that since in the compilation database is an absolute path
"/remote/users/rgeissler/wk/tmp/clang-scan-deps" then clang would change the
current directory to this folder (and do the same for each entry of the
database), before running the scan, but apparently it doesn't (or it doesn't
work as expected). It's a bit strange, since in the code, it looks like you try
to do that:
https://github.com/llvm/llvm-project/blob/master/clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp#L208

llvm::Error DependencyScanningWorker::computeDependencies(
    const std::string &Input, StringRef WorkingDirectory,
    const CompilationDatabase &CDB, DependencyConsumer &Consumer) {
  RealFS->setCurrentWorkingDirectory(WorkingDirectory);
  ...

where normally "WorkingDirectory" is the "directory" entry of the compilation
database.

Is it expected ?

Cheers,
Romain

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