Add MCP server for AI agent integration with Buck2

Implements a Model Context Protocol (MCP) server that allows AI agents
to interact with Buck2 through a JSON-RPC interface over stdio. Features:

- MCP protocol implementation with JSON-RPC 2.0 transport
- Daemon client for connecting to running Buck2 daemon
- Tools: buck2_build, buck2_query (cquery/uquery), buck2_targets
- Async build support with operation polling for long-running builds
- Operation manager for tracking and cancelling async operations

Signed-off-by: Daniel Hodges <hodgesd@meta.com>

Author: hodgesds

Cargo.toml

@@ -48,6 +48,7 @@ members = [
     "app/buck2_grpc",
     "app/buck2_health_check",
     "app/buck2_health_check_proto",
+    "app/buck2_mcp",
     "app/buck2_http",
     "app/buck2_install_proto",
     "app/buck2_interpreter",
@@ -434,6 +435,7 @@ buck2_host_sharing_proto = { path = "app/buck2_host_sharing_proto" }
 buck2_http = { path = "app/buck2_http" }
 buck2_install_proto = { path = "app/buck2_install_proto" }
 buck2_interpreter = { path = "app/buck2_interpreter" }
+buck2_mcp = { path = "app/buck2_mcp" }
 buck2_interpreter_for_build = { path = "app/buck2_interpreter_for_build" }
 buck2_interpreter_for_build_tests = { path = "app/buck2_interpreter_for_build_tests" }
 buck2_miniperf = { path = "app/buck2_miniperf" }

app/buck2_mcp/BUCK

@@ -0,0 +1,49 @@
+load("@fbcode//buck2:buck_rust_binary.bzl", "buck_rust_binary")
+load("@fbsource//tools/build_defs:rust_library.bzl", "rust_library")
+
+oncall("build_infra")
+
+rust_library(
+    name = "buck2_mcp",
+    srcs = glob([
+        "src/**/*.rs",
+    ]),
+    test_deps = [
+        "fbsource//third-party/rust:tempfile",
+    ],
+    deps = [
+        "fbsource//third-party/rust:async-trait",
+        "fbsource//third-party/rust:chrono",
+        "fbsource//third-party/rust:dirs",
+        "fbsource//third-party/rust:futures",
+        "fbsource//third-party/rust:prost-0-13-4",
+        "fbsource//third-party/rust:serde",
+        "fbsource//third-party/rust:serde_json",
+        "fbsource//third-party/rust:tokio",
+        "fbsource//third-party/rust:tonic-0-12-3",
+        "fbsource//third-party/rust:tracing",
+        "fbsource//third-party/rust:tracing-subscriber",
+        "fbsource//third-party/rust:uuid",
+        "//buck2/app/buck2_cli_proto:buck2_cli_proto",
+        "//buck2/app/buck2_common:buck2_common",
+        "//buck2/app/buck2_core:buck2_core",
+        "//buck2/app/buck2_error:buck2_error",
+        "//buck2/app/buck2_fs:buck2_fs",
+        "//buck2/app/buck2_util:buck2_util",
+    ],
+)
+
+buck_rust_binary(
+    name = "buck2-mcp",
+    srcs = ["src/bin/buck2-mcp.rs"],
+    crate = "buck2_mcp_bin",
+    crate_root = "src/bin/buck2-mcp.rs",
+    deps = [
+        ":buck2_mcp",
+        "fbsource//third-party/rust:tokio",
+        "fbsource//third-party/rust:tracing",
+        "fbsource//third-party/rust:tracing-subscriber",
+        "//buck2/app/buck2_error:buck2_error",
+        "//buck2/app/buck2_fs:buck2_fs",
+    ],
+)

app/buck2_mcp/Cargo.toml

@@ -0,0 +1,35 @@
+[package]
+name = "buck2_mcp"
+description = "Buck2 MCP (Model Context Protocol) server for AI agent integration"
+edition = "2024"
+license = { workspace = true }
+repository = { workspace = true }
+version = "0.1.0"
+
+[[bin]]
+name = "buck2-mcp"
+path = "src/bin/buck2-mcp.rs"
+
+[dependencies]
+async-trait = { workspace = true }
+chrono = { workspace = true }
+dirs = { workspace = true }
+futures = { workspace = true }
+prost = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
+tokio = { workspace = true }
+tonic = { workspace = true }
+tracing = { workspace = true }
+tracing-subscriber = { workspace = true }
+uuid = { workspace = true }
+
+buck2_cli_proto = { workspace = true }
+buck2_common = { workspace = true }
+buck2_core = { workspace = true }
+buck2_error = { workspace = true }
+buck2_fs = { workspace = true }
+buck2_util = { workspace = true }
+
+[dev-dependencies]
+tempfile = { workspace = true }

app/buck2_mcp/src/bin/buck2-mcp.rs

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is dual-licensed under either the MIT license found in the
+ * LICENSE-MIT file in the root directory of this source tree or the Apache
+ * License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+ * of this source tree. You may select, at your option, one of the
+ * above-listed licenses.
+ */
+
+//! Buck2 MCP server binary entry point.
+
+use std::env;
+
+use tracing::info;
+use tracing_subscriber::EnvFilter;
+
+#[tokio::main]
+async fn main() -> buck2_error::Result<()> {
+    // Initialize tracing to stderr (stdout is used for MCP protocol)
+    tracing_subscriber::fmt()
+        .with_env_filter(EnvFilter::from_default_env())
+        .with_writer(std::io::stderr)
+        .init();
+
+    info!("Starting Buck2 MCP server");
+
+    let working_dir = env::current_dir()
+        .map_err(|e| {
+            buck2_error::buck2_error!(
+                buck2_error::ErrorTag::Environment,
+                "Failed to get current directory: {}",
+                e
+            )
+        })?
+        .to_string_lossy()
+        .to_string();
+
+    info!("Working directory: {}", working_dir);
+
+    let mut server = buck2_mcp::mcp::server::McpServer::new(working_dir);
+    server.run().await
+}

app/buck2_mcp/src/daemon.rs

@@ -0,0 +1,13 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is dual-licensed under either the MIT license found in the
+ * LICENSE-MIT file in the root directory of this source tree or the Apache
+ * License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+ * of this source tree. You may select, at your option, one of the
+ * above-listed licenses.
+ */
+
+//! Buck2 daemon client wrapper.
+
+pub mod client;