rust-lang/rust · critical

command did not execute successfully: {:?} expected success,

Error message

command did not execute successfully: {:?}
expected success, got: {}

What it means

Thrown by execute() (build.rs:92-109) — the shared command runner for rustc_llvm's build script — when an invoked command exits with a non-success status. It panics with the full command (`{:?}`) and its ExitStatus. The commands run through execute()/output()/stderr() are almost always `llvm-config` invocations (e.g. `--components`, `--help`, `--link-shared --libs`, `--cxxflags`, `--ldflags`), so a failure here means llvm-config itself errored.

Source

Thrown at compiler/rustc_llvm/build.rs:102

        if entry.file_type().unwrap().is_dir() {
            stack.extend(path.read_dir().unwrap().map(|e| e.unwrap()));
        } else {
            println!("cargo:rerun-if-changed={}", path.display());
        }
    }
}

#[track_caller]
fn execute(cmd: &mut Command) -> Output {
    let output = match cmd.output() {
        Ok(status) => status,
        Err(e) => {
            println!("\n\nfailed to execute command: {cmd:?}\nerror: {e}\n\n");
            std::process::exit(1);
        }
    };
    if !output.status.success() {
        panic!(
            "command did not execute successfully: {:?}\n\
             expected success, got: {}",
            cmd, output.status
        );
    }
    output
}

#[track_caller]
fn output(cmd: &mut Command) -> String {
    String::from_utf8(execute(cmd.stderr(Stdio::inherit())).stdout).unwrap()
}
#[track_caller]
fn stderr(cmd: &mut Command) -> String {
    String::from_utf8(execute(cmd).stderr).unwrap()
}

enum LlvmConfigOutput {

View on GitHub (pinned to 22057b88b0)

Solutions

1. Reproduce the exact failing command shown in the panic (the `{:?}` Command debug output) by running it manually in a shell, then read llvm-config's stderr to find the real cause.
2. Ensure LLVM_CONFIG points to a working llvm-config matching the LLVM version rustc expects; rebuild/reinstall LLVM if its install is corrupt.
3. Prefer building LLVM through bootstrap (`./x.py build` with the default src/llvm-project) so the toolchain and llvm-config stay consistent.
4. If cross-compiling, verify you are using the host-side llvm-config as bootstrap intends and that host/target LLVM are configured identically.

# Dry-run every external tool the build script can invoke before the real build
for tool in llvm-config cmake ninja clang cc; do
  command -v "$tool" >/dev/null 2>&1 || { echo "missing required tool: $tool"; exit 1; }
done
"$LLVM_CONFIG" --version >/dev/null 2>&1 || { echo "llvm-config not runnable"; exit 1; }

# Wrap the cargo/x.py build so transient external-command failures are retried
n=0
until ./x.py build compiler/rustc_llvm; do
  n=$((n+1)); [ "$n" -lt 3 ] || { echo "build failed after $n attempts"; exit 1; }
  echo "retrying build (attempt $n)..."
done

When it happens

Trigger: llvm-config exits non-zero: the configured LLVM_CONFIG path points at a broken or mismatched LLVM build; the LLVM installation is missing libraries llvm-config expects; `llvm-config --help` (build.rs:193), `--components` (build.rs:228), `--cxxflags`, `--libs`, or `--ldflags` fails. Any execute()/output()/stderr() call in main() can surface it.

Common situations: Building rustc against a hand-built or system LLVM that is incomplete, corrupted, or the wrong version; LLVM_CONFIG pointing to a stale binary after an LLVM rebuild; cross-compiling where the host llvm-config cannot run on the target; missing system libraries that llvm-config tries to report.

Related errors

• REAL_LIBRARY_PATH_VAR
• LLVM_CONFIG was not set
• require llvm component {component} but wasn't found
• TARGET was not set
• HOST was not set

AI-assisted analysis of rust-lang/rust@22057b88b0 (2026-08-03). Data as JSON: /data/errors/f4cb778433bdb77d.json. Report an issue: GitHub.