Support no_std in Prost toolchain

Author: lorenz

docs/src/rust_prost.md

@@ -166,9 +166,9 @@ A rule for generating a Rust library using Prost.
 ## rust_prost_toolchain
 
 <pre>
-rust_prost_toolchain(<a href="#rust_prost_toolchain-name">name</a>, <a href="#rust_prost_toolchain-include_transitive_deps">include_transitive_deps</a>, <a href="#rust_prost_toolchain-prost_opts">prost_opts</a>, <a href="#rust_prost_toolchain-prost_plugin">prost_plugin</a>, <a href="#rust_prost_toolchain-prost_plugin_flag">prost_plugin_flag</a>,
-                     <a href="#rust_prost_toolchain-prost_runtime">prost_runtime</a>, <a href="#rust_prost_toolchain-prost_types">prost_types</a>, <a href="#rust_prost_toolchain-proto_compiler">proto_compiler</a>, <a href="#rust_prost_toolchain-tonic_opts">tonic_opts</a>, <a href="#rust_prost_toolchain-tonic_plugin">tonic_plugin</a>,
-                     <a href="#rust_prost_toolchain-tonic_plugin_flag">tonic_plugin_flag</a>, <a href="#rust_prost_toolchain-tonic_runtime">tonic_runtime</a>)
+rust_prost_toolchain(<a href="#rust_prost_toolchain-name">name</a>, <a href="#rust_prost_toolchain-include_transitive_deps">include_transitive_deps</a>, <a href="#rust_prost_toolchain-is_nostd">is_nostd</a>, <a href="#rust_prost_toolchain-prost_opts">prost_opts</a>, <a href="#rust_prost_toolchain-prost_plugin">prost_plugin</a>,
+                     <a href="#rust_prost_toolchain-prost_plugin_flag">prost_plugin_flag</a>, <a href="#rust_prost_toolchain-prost_runtime">prost_runtime</a>, <a href="#rust_prost_toolchain-prost_types">prost_types</a>, <a href="#rust_prost_toolchain-proto_compiler">proto_compiler</a>, <a href="#rust_prost_toolchain-tonic_opts">tonic_opts</a>,
+                     <a href="#rust_prost_toolchain-tonic_plugin">tonic_plugin</a>, <a href="#rust_prost_toolchain-tonic_plugin_flag">tonic_plugin_flag</a>, <a href="#rust_prost_toolchain-tonic_runtime">tonic_runtime</a>)
 </pre>
 
 Rust Prost toolchain rule.
@@ -180,6 +180,7 @@ Rust Prost toolchain rule.
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="rust_prost_toolchain-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
 | <a id="rust_prost_toolchain-include_transitive_deps"></a>include_transitive_deps |  Whether to include transitive dependencies. If set to True, all transitive dependencies will directly accessible by the dependent crate.   | Boolean | optional |  `False`  |
+| <a id="rust_prost_toolchain-is_nostd"></a>is_nostd |  If a no_std tag should be put into the generated code.   | Boolean | optional |  `False`  |
 | <a id="rust_prost_toolchain-prost_opts"></a>prost_opts |  Additional options to add to Prost.   | List of strings | optional |  `[]`  |
 | <a id="rust_prost_toolchain-prost_plugin"></a>prost_plugin |  Additional plugins to add to Prost.   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
 | <a id="rust_prost_toolchain-prost_plugin_flag"></a>prost_plugin_flag |  Prost plugin flag format. (e.g. `--plugin=protoc-gen-prost=%s`)   | String | optional |  `"--plugin=protoc-gen-prost=%s"`  |

extensions/prost/private/protoc_wrapper.rs

@@ -159,7 +159,11 @@ fn generate_lib_rs(
     is_nostd: bool,
 ) -> String {
     let mut contents = vec![
-        if is_nostd { "#![no_std]".to_string() } else { "".to_string() },
+        if is_nostd {
+            "#![no_std]".to_string()
+        } else {
+            "".to_string()
+        },
         "// @generated".to_string(),
         "".to_string(),
     ];
@@ -988,7 +992,6 @@ fn escape_keyword(s: String) -> String {
 
 #[cfg(test)]
 mod test {
-
     use super::*;
 
     use prost_types::{FieldDescriptorProto, ServiceDescriptorProto};