Add example usage of third party crates.

examples/bzlmod/hello_world/BUILD.bazel

@@ -2,9 +2,18 @@ load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_doc")
 
 package(default_visibility = ["//visibility:public"])
 
+rust_binary(
+    name = "hello_log",
+    srcs = ["hello_log.rs"],
+    deps = [
+        "@crates//:env_logger",
+        "@crates//:log",
+    ],
+)
+
 rust_binary(
     name = "hello_world",
-    srcs = ["src/main.rs"],
+    srcs = ["hello_world.rs"],
 )
 
 rust_doc(

examples/bzlmod/hello_world/Cargo.toml

@@ -0,0 +1,15 @@
+# This package is not used. It's a dummy package that declares dependencies that
+# you can then access from @crates//:<dep>.
+[package]
+name = "dummy"
+version = "0.1.0"
+edition = "2021"
+
+[[bin]]
+name = "dummy"
+# Some arbitrary .rs file that exists.
+path = "hello_world.rs"
+
+[dependencies]
+env_logger = "0.9.2"
+log = "0.4.17"

examples/bzlmod/hello_world/MODULE.bazel

@@ -17,3 +17,17 @@ use_repo(
 )
 
 register_toolchains("@rust_toolchains//:all")
+
+# Use a toml file to generate your dependencies like so:
+crate = use_extension(
+    "@rules_rust//crate_universe:extension.bzl",
+    "crate",
+)
+crate.from_cargo(
+    # This is optional, but if you need crate.annotation, then this is the
+    # bzlmod equivalent.
+    annotation_files = ["//:annotations.json"],
+    cargo_lockfile = "//:Cargo.lock",
+    manifests = ["//:Cargo.toml"],
+)
+use_repo(crate, "crates")

examples/bzlmod/hello_world/annotations.json

@@ -0,0 +1,13 @@
+{
+  "env_logger": [
+    {
+      "version": "0.9.2",
+      "additive_build_file_content": "\n# Extra stuff here"
+    }
+  ],
+  "log": [
+    {
+      "additive_build_file_content": "\n# Extra stuff here"
+    }
+  ]
+}

examples/bzlmod/hello_world/hello_log.rs

@@ -0,0 +1,22 @@
+// Copyright 2023 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+fn main() {
+    env_logger::init();
+    if log::log_enabled!(log::Level::Info) {
+        log::info!("Hello log!");
+    } else {
+        println!("Logging disabled");
+    }
+}