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/prost.bzl

@@ -86,6 +86,9 @@ def _compile_proto(
     additional_args.add("--additional_srcs={}".format(",".join([f.path for f in all_additional_srcs.to_list()])))
     additional_args.add_all(prost_toolchain.prost_opts + prost_opts, format_each = "--prost_opt=%s")
 
+    if prost_toolchain.is_nostd:
+        additional_args.add("--is_nostd")
+
     if prost_toolchain.tonic_plugin:
         tonic_plugin = prost_toolchain.tonic_plugin[DefaultInfo].files_to_run
         additional_args.add(prost_toolchain.tonic_plugin_flag % tonic_plugin.executable.path)
@@ -442,6 +445,7 @@ def _rust_prost_toolchain_impl(ctx):
         tonic_plugin_flag = ctx.attr.tonic_plugin_flag,
         tonic_runtime = ctx.attr.tonic_runtime,
         include_transitive_deps = ctx.attr.include_transitive_deps,
+        is_nostd = ctx.attr.is_nostd,
     )]
 
 rust_prost_toolchain = rule(
@@ -453,6 +457,10 @@ rust_prost_toolchain = rule(
             doc = "Whether to include transitive dependencies. If set to True, all transitive dependencies will directly accessible by the dependent crate.",
             default = False,
         ),
+        "is_nostd": attr.bool(
+            doc = "If a no_std tag should be put into the generated code.",
+            default = False,
+        ),
         "prost_opts": attr.string_list(
             doc = "Additional options to add to Prost.",
         ),

extensions/prost/private/protoc_wrapper.rs

@@ -156,8 +156,17 @@ fn generate_lib_rs(
     is_tonic: bool,
     direct_dep_crate_names: Vec<String>,
     additional_content: String,
+    is_nostd: bool,
 ) -> String {
-    let mut contents = vec!["// @generated".to_string(), "".to_string()];
+    let mut contents = vec![
+        if is_nostd {
+            "#![no_std]".to_string()
+        } else {
+            "".to_string()
+        },
+        "// @generated".to_string(),
+        "".to_string(),
+    ];
     for crate_name in direct_dep_crate_names {
         contents.push(format!("pub use {crate_name};"));
     }
@@ -457,6 +466,9 @@ struct Args {
     /// Whether to generate tonic code.
     is_tonic: bool,
 
+    // Whether to put a no_std tag into the generated code.
+    is_nostd: bool,
+
     /// Extra arguments to pass to protoc.
     extra_args: Vec<String>,
 }
@@ -479,6 +491,7 @@ impl Args {
         let mut tonic_or_prost_opts = Vec::new();
         let mut direct_dep_crate_names = Vec::new();
         let mut is_tonic = false;
+        let mut is_nostd = false;
 
         let mut extra_args = Vec::new();
 
@@ -501,6 +514,10 @@ impl Args {
                 is_tonic = true;
                 return;
             }
+            if arg == "--is_nostd" {
+                is_nostd = true;
+                return;
+            }
 
             if !arg.contains('=') {
                 extra_args.push(arg);
@@ -644,6 +661,7 @@ impl Args {
             proto_paths,
             direct_dep_crate_names,
             is_tonic,
+            is_nostd,
             label: label.unwrap(),
             extra_args,
         })
@@ -748,6 +766,7 @@ fn main() {
         proto_paths,
         direct_dep_crate_names,
         is_tonic,
+        is_nostd,
         extra_args,
     } = Args::parse().expect("Failed to parse args");
 
@@ -917,6 +936,7 @@ fn main() {
             is_tonic,
             direct_dep_crate_names,
             additional_content,
+            is_nostd,
         ),
     )
     .expect("Failed to write file.");
@@ -972,7 +992,6 @@ fn escape_keyword(s: String) -> String {
 
 #[cfg(test)]
 mod test {
-
     use super::*;
 
     use prost_types::{FieldDescriptorProto, ServiceDescriptorProto};