Debugging C++ code does not work when built with Bazel on MacOS

Question

I have started a C++ project in Visual Studio Code with Bazel build system. But debugging does not work in the IDE when the binary is built using Bazel.

I can debug application when built with clang++ -g main.cpp -o sample.

My setup: OS: MacOS, Bazel: release 0.17.2-homebrew, VS Code: 1.27.2

Which is caused by the way Bazel compiles. Is there any workaround to make debugging work?

Here is a minimal example. Just put a breakpoint in the editor, run debugging, and observe a breakpoint not being hit:

├── .vscode
│   ├── launch.json
│   └── tasks.json
├── BUILD
├── WORKSPACE
├── main.cpp
└── sample.code-workspace

.vscode/launch.json

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "(lldb) Launch",
            "type": "cppdbg",
            "request": "launch",
            "program": "${workspaceRoot}/bazel-bin/sample",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${workspaceFolder}",
            "externalConsole": false,
            "MIMode": "lldb",
            "preLaunchTask": "bazel build",
        }
    ]
}

.vscode/tasks.json

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "bazel build",
            "type": "shell",
            "command": "bazel",
            "args": [
                "build",
                "--compilation_mode=dbg",
                "sample"
            ],
            "group": {
                "kind": "build",
                "isDefault": true
            }
        }
    ]
}

BUILD

cc_binary(
    name = "sample",
    srcs = ["main.cpp"],
    visibility = ["//main:__pkg__"],
)

main.cpp

#include <iostream>

int main() {
    std::cout << "tests" << std::endl;
    return 0;
}

sample.code-workspace

{
    "folders": [ {"path": "."} ],
    "settings": {}
}

---

Upd. 1

Tried debugging bazel-built executable and manually-built directly with lldb:

Bazel-built binary bazel build --compilation_mode=dbg sample

lldb bazel-bin/sample
(lldb) breakpoint set -n main
Breakpoint 1: 13 locations.
(lldb) r
Process 24391 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x00000001000021b0 sample`main
sample`main:
->  0x1000021b0 <+0>: pushq  %rbp
    0x1000021b1 <+1>: movq   %rsp, %rbp
    0x1000021b4 <+4>: subq   $0x20, %rsp
    0x1000021b8 <+8>: movq   0xe51(%rip), %rdi         ; (void *)0x00007fff9c93a660: std::__1::cout
Target 0: (sample) stopped.

Manually-built binary clang++ -g main.cpp -o sample

lldb sample
(lldb) breakpoint set -n main
Breakpoint 1: where = sample`main + 29 at main.cpp:4, address = 0x0000000100000f9d
(lldb) r
Process 24410 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100000f9d sample`main at main.cpp:4
   1    #include <iostream>
   2    
   3    int main() {
-> 4        std::cout << "tests" << std::endl;
   5        return 0;
   6    }
Target 0: (sample) stopped.

After looking up the "debug notes" in the executable (thanks to this answer)

nm -pa bazel-bin/sample | grep OSO
000000005bb7c96b - 03 0001   OSO /private/var/tmp/_bazel_teivaz/1e731ee5ae5a3ce6177976984318ec76/bazel-sandbox/1688134534644271312/execroot/__main__/bazel-out/darwin-dbg/bin/_objs/sample/main.o

I figured out that these paths point to the sandbox environment that Bazel used to build. And this path is no longer accessible.

This is likely caused by a known issue in Bazel #5545

---

Upd. 2

After updating Bazel to version 0.17.2 (where the issue #5545 is already fixed) this issue still occurs.

---

Upd. 3

In the end it turns out to be the Bazel problem. I have created an issue here #6327

Answer 1

(Promoting updates to answer): Looks like a known issue: #6327

Answer 2

For anyone else stumbling upon this issue, the following worked for me (March 2022):

.bazelrc:

build:debug -c dbg
build:debug --features=oso_prefix_is_pwd

Then build using:

bazel build --config debug //project/path:name

The .bazelrc can be either in your home directory, or in the same directory as bazel's WORKSPACE file