rust-lang/rust · warning · anyhow::Error

Please set `rust-analyzer.profiling.memoryProfile` to the pa

Error message

Please set `rust-analyzer.profiling.memoryProfile` to the path where you want to save the profile.

What it means

Returned by handle_memory_usage in the dhat-enabled arm when the server has no output path configured (config.dhat_output_file() returns None). Even on a profiling build the user must tell rust-analyzer where to write the profile, via the rust-analyzer.profiling.memoryProfile setting.

Source

Thrown at src/tools/rust-analyzer/crates/rust-analyzer/src/handlers/request.rs:153

            "Memory profiling is not enabled for this build of rust-analyzer.\n\n\
            To build rust-analyzer with profiling support, pass `--features dhat --profile dev-rel` to `cargo build`
            when building from source, or pass `--enable-profiling` to `cargo xtask`."
        ))
    }
    #[cfg(feature = "dhat")]
    {
        if let Some(dhat_output_file) = _state.config.dhat_output_file() {
            let mut profiler = crate::DHAT_PROFILER.lock().unwrap();
            let old_profiler = profiler.take();
            // Need to drop the old profiler before creating a new one.
            drop(old_profiler);
            *profiler = Some(dhat::Profiler::builder().file_name(&dhat_output_file).build());
            Ok(format!(
                "Memory profile was saved successfully to {dhat_output_file}.\n\n\
                See https://docs.rs/dhat/latest/dhat/#viewing for how to inspect the profile."
            ))
        } else {
            Err(anyhow::anyhow!(
                "Please set `rust-analyzer.profiling.memoryProfile` to the path where you want to save the profile."
            ))
        }
    }
}

pub(crate) fn handle_view_syntax_tree(
    snap: GlobalStateSnapshot,
    params: lsp_ext::ViewSyntaxTreeParams,
) -> anyhow::Result<String> {
    let _p = tracing::info_span!("handle_view_syntax_tree").entered();
    let id = try_default!(from_proto::file_id(&snap, &params.text_document.uri)?);
    let res = snap.analysis.view_syntax_tree(id)?;
    Ok(res)
}

pub(crate) fn handle_view_hir(
    snap: GlobalStateSnapshot,

View on GitHub (pinned to 7088e4b63a)

Solutions

Set rust-analyzer.profiling.memoryProfile to an absolute writable file path in the client/extension settings.
Ensure the directory portion of that path exists and is writable by the server process.
Re-trigger the profiling request after saving the setting.

Example fix

// settings.json (VS Code) — before: no setting
{}

// after
{
  "rust-analyzer.profiling.memoryProfile": "/home/me/ra-dhat.json"
}

Defensive patterns

Strategy: validation

Validate before calling

// Validate the memoryProfile setting is a writable path before sending the request:
fn profile_path_ok(p: &str) -> bool {
    let path = std::path::Path::new(p);
    path.is_absolute() && path.parent().map(|d| d.exists() && std::fs::metadata(d).map(|m| !m.permissions().readonly()).unwrap_or(false)).unwrap_or(false)
}

Type guard

null

Try / catch

match ra.handle_memory_usage() {
    Ok(msg) => Ok(msg),
    Err(e) if e.to_string().contains("memoryProfile") => {
        eprintln!("set rust-analyzer.profiling.memoryProfile to a writable file path, then retry");
        Err(e)
    }
    Err(e) => Err(e),
}

Prevention

Always configure rust-analyzer.profiling.memoryProfile before triggering profiling.
Use an absolute path in a directory the server can write.
Re-verify the setting after extension updates in case it was renamed.

When it happens

Trigger: Invoking the memory profiling request on a correctly-built (dhat) rust-analyzer while the client has not set rust-analyzer.profiling.memoryProfile to a writable path.

Common situations: Enabling the profiling command for the first time without configuring the output path; the setting being cleared/renamed after an extension update; pointing at an unwritable directory (handled separately at write time).

Related errors

AI-assisted analysis of rust-lang/rust@7088e4b63a (2026-08-10). Data as JSON: /api/errors/e109de1369801591. Report an issue: GitHub.