Make prost a no_std compatible library, and prost-build able to gen…

…erate `no_std` code

The alternative is to get collections types from `core` and `alloc`.
In the `no_std` mode in `prost_build`, we force it to always use BTreeMap
since HashMap was not stabilized in `alloc::collections` library.

The functionality is identical and the only incompatibilities in the interface
are that we cannot use `std::error::Error` or `std::io::Error` in `no_std` mode
because these types have not been moved to `alloc` and there is no alternative.

This also uprevs `bytes` dependency to 0.5, and fixes up breakage after IntoBuf api
is removed in `bytes` crate.

.travis.yml

@@ -14,13 +14,15 @@ os:
   - linux
   - osx
 
+# After 1.36.0 alloc crate is stable and we can avoid special handling below
 rust:
-  - 1.32.0
+  - 1.36.0
   - nightly
 
 script:
-  - cargo build --verbose --all --exclude benchmarks
-  - cargo test --verbose --all --exclude benchmarks
+  - cargo build --verbose --all --exclude benchmarks --exclude test-alloc
+  - cargo test --verbose --all --exclude benchmarks --exclude test-alloc
   - if [[ $TRAVIS_RUST_VERSION = nightly* ]]; then
+      cargo test --verbose test-alloc 
       cargo bench --verbose --no-run;
     fi

Cargo.toml

@@ -25,6 +25,7 @@ members = [
   "protobuf",
   "tests",
   "tests-2015",
+  "tests-alloc",
 ]
 exclude = [
   # The fuzz crate can't be compiled or tested without the 'cargo fuzz' command,
@@ -33,11 +34,15 @@ exclude = [
 ]
 
 [features]
-default = ["prost-derive"]
+default = ["prost-derive", "std"]
 no-recursion-limit = []
+std = []
+   # When std is disabled, we attempt to provide no_std support in prost
+   # Config::use_alloc_collections() should be set when using prost_build in your build.rs
+   # so that generated files will not have std:: either, and will use alloc crate instead
 
 [dependencies]
-bytes = "0.4.7"
+bytes = { git = "https://github.com/tokio-rs/bytes", rev = "c17e40115f5bb2a2db71ed90dceae6ec643dc024", default-features = false }
 prost-derive = { version = "0.5.0", path = "prost-derive", optional = true }
 
 [dev-dependencies]

prost-build/src/code_generator.rs

@@ -17,6 +17,7 @@ use crate::ast::{Comments, Method, Service};
 use crate::extern_paths::ExternPaths;
 use crate::ident::{match_ident, to_snake, to_upper_camel};
 use crate::message_graph::MessageGraph;
+use crate::CollectionsLib;
 use crate::Config;
 
 #[derive(PartialEq)]
@@ -366,12 +367,14 @@ impl<'a> CodeGenerator<'a> {
         self.buf.push_str(&to_snake(field.name()));
         self.buf.push_str(": ");
         if repeated {
-            self.buf.push_str("::std::vec::Vec<");
+            self.buf.push_str(self.config.collections_lib.to_str());
+            self.buf.push_str("::vec::Vec<");
         } else if optional {
-            self.buf.push_str("::std::option::Option<");
+            self.buf.push_str("::core::option::Option<");
         }
         if boxed {
-            self.buf.push_str("::std::boxed::Box<");
+            self.buf.push_str(self.config.collections_lib.to_str());
+            self.buf.push_str("::boxed::Box<");
         }
         self.buf.push_str(&ty);
         if boxed {
@@ -403,7 +406,7 @@ impl<'a> CodeGenerator<'a> {
         self.append_doc();
         self.push_indent();
 
-        let btree_map = self
+        let btree_map = (self.config.collections_lib != CollectionsLib::Std) || self
             .config
             .btree_map
             .iter()
@@ -426,8 +429,9 @@ impl<'a> CodeGenerator<'a> {
         self.append_field_attributes(msg_name, field.name());
         self.push_indent();
         self.buf.push_str(&format!(
-            "pub {}: ::std::collections::{}<{}, {}>,\n",
+            "pub {}: {}::collections::{}<{}, {}>,\n",
             to_snake(field.name()),
+            self.config.collections_lib.to_str(),
             rust_ty,
             key_ty,
             value_ty
@@ -459,7 +463,7 @@ impl<'a> CodeGenerator<'a> {
         self.append_field_attributes(fq_message_name, oneof.name());
         self.push_indent();
         self.buf.push_str(&format!(
-            "pub {}: ::std::option::Option<{}>,\n",
+            "pub {}: ::core::option::Option<{}>,\n",
             to_snake(oneof.name()),
             name
         ));
@@ -713,8 +717,8 @@ impl<'a> CodeGenerator<'a> {
             Type::Int32 | Type::Sfixed32 | Type::Sint32 | Type::Enum => String::from("i32"),
             Type::Int64 | Type::Sfixed64 | Type::Sint64 => String::from("i64"),
             Type::Bool => String::from("bool"),
-            Type::String => String::from("std::string::String"),
-            Type::Bytes => String::from("std::vec::Vec<u8>"),
+            Type::String => format!("{}::string::string", self.config.collections_lib.to_str()),
+            Type::Bytes => format!("{}::vec::Vec<u8>", self.config.collections_lib.to_str()),
             Type::Group | Type::Message => self.resolve_ident(field.type_name()),
         }
     }

prost-build/src/lib.rs

@@ -165,11 +165,32 @@ pub trait ServiceGenerator {
     fn finalize(&mut self, _buf: &mut String) {}
 }
 
+/// Configuration enum for whether to use `std` prefixes or `alloc` prefixes in generated code
+///
+/// This option also forces Btree everywhere, overriding the BtreeMap options,
+/// since HashMap is not in alloc::collections, only std (it requires randomness)
+/// 
+#[derive(PartialEq)]
+pub enum CollectionsLib {
+    Std,
+    Alloc,
+}
+
+impl CollectionsLib {
+    pub fn to_str(&self) -> &'static str {
+        match self {
+            CollectionsLib::Std => { "::std" },
+            CollectionsLib::Alloc => { "::alloc" },
+        }
+    }
+}
+
 /// Configuration options for Protobuf code generation.
 ///
 /// This configuration builder can be used to set non-default code generation options.
 pub struct Config {
     service_generator: Option<Box<dyn ServiceGenerator>>,
+    collections_lib: CollectionsLib,
     btree_map: Vec<String>,
     type_attributes: Vec<(String, String)>,
     field_attributes: Vec<(String, String)>,
@@ -460,6 +481,15 @@ impl Config {
         self
     }
 
+    /// Configure the code generator to use the `::alloc` namespace rather than `::std`, and Btree everywhere
+    /// rather than `std`.
+    ///
+    /// This allows generated code to be used in a `#![no_std]` crate
+    pub fn use_alloc_collections_lib(&mut self) -> &mut Self {
+        self.collections_lib = CollectionsLib::Alloc;
+        self
+    }
+
     /// Configures the output directory where generated Rust files will be written.
     ///
     /// If unset, defaults to the `OUT_DIR` environment variable. `OUT_DIR` is set by Cargo when
@@ -581,6 +611,7 @@ impl default::Default for Config {
     fn default() -> Config {
         Config {
             service_generator: None,
+            collections_lib: CollectionsLib::Std,
             btree_map: Vec::new(),
             type_attributes: Vec::new(),
             field_attributes: Vec::new(),

prost-types/Cargo.toml

@@ -14,6 +14,10 @@ edition = "2018"
 doctest = false
 test = false
 
+[features]
+default = ["std"]
+std = []
+
 [dependencies]
 bytes = "0.4.7"
-prost = { version = "0.5.0", path = ".." }
+prost = { version = "0.5.0", path = "..", default-features = false }

prost-types/src/compiler.rs

@@ -2,15 +2,15 @@
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct Version {
     #[prost(int32, optional, tag="1")]
-    pub major: ::std::option::Option<i32>,
+    pub major: ::core::option::Option<i32>,
     #[prost(int32, optional, tag="2")]
-    pub minor: ::std::option::Option<i32>,
+    pub minor: ::core::option::Option<i32>,
     #[prost(int32, optional, tag="3")]
-    pub patch: ::std::option::Option<i32>,
+    pub patch: ::core::option::Option<i32>,
     /// A suffix for alpha, beta or rc release, e.g., "alpha-1", "rc2". It should
     /// be empty for mainline stable releases.
     #[prost(string, optional, tag="4")]
-    pub suffix: ::std::option::Option<std::string::String>,
+    pub suffix: ::core::option::Option<alloc::string::String>,
 }
 /// An encoded CodeGeneratorRequest is written to the plugin's stdin.
 #[derive(Clone, PartialEq, ::prost::Message)]
@@ -19,10 +19,10 @@ pub struct CodeGeneratorRequest {
     /// code generator should generate code only for these files.  Each file's
     /// descriptor will be included in proto_file, below.
     #[prost(string, repeated, tag="1")]
-    pub file_to_generate: ::std::vec::Vec<std::string::String>,
+    pub file_to_generate: ::std::vec::Vec<alloc::string::String>,
     /// The generator parameter passed on the command-line.
     #[prost(string, optional, tag="2")]
-    pub parameter: ::std::option::Option<std::string::String>,
+    pub parameter: ::core::option::Option<alloc::string::String>,
     /// FileDescriptorProtos for all files in files_to_generate and everything
     /// they import.  The files will appear in topological order, so each file
     /// appears before any file that imports it.
@@ -41,7 +41,7 @@ pub struct CodeGeneratorRequest {
     pub proto_file: ::std::vec::Vec<super::FileDescriptorProto>,
     /// The version number of protocol compiler.
     #[prost(message, optional, tag="3")]
-    pub compiler_version: ::std::option::Option<Version>,
+    pub compiler_version: ::core::option::Option<Version>,
 }
 /// The plugin writes an encoded CodeGeneratorResponse to stdout.
 #[derive(Clone, PartialEq, ::prost::Message)]
@@ -55,7 +55,7 @@ pub struct CodeGeneratorResponse {
     /// unparseable -- should be reported by writing a message to stderr and
     /// exiting with a non-zero status code.
     #[prost(string, optional, tag="1")]
-    pub error: ::std::option::Option<std::string::String>,
+    pub error: ::core::option::Option<alloc::string::String>,
     #[prost(message, repeated, tag="15")]
     pub file: ::std::vec::Vec<code_generator_response::File>,
 }
@@ -75,7 +75,7 @@ pub mod code_generator_response {
         /// this writing protoc does not optimize for this -- it will read the entire
         /// CodeGeneratorResponse before writing files to disk.
         #[prost(string, optional, tag="1")]
-        pub name: ::std::option::Option<std::string::String>,
+        pub name: ::core::option::Option<alloc::string::String>,
         /// If non-empty, indicates that the named file should already exist, and the
         /// content here is to be inserted into that file at a defined insertion
         /// point.  This feature allows a code generator to extend the output
@@ -114,9 +114,9 @@ pub mod code_generator_response {
         ///
         /// If |insertion_point| is present, |name| must also be present.
         #[prost(string, optional, tag="2")]
-        pub insertion_point: ::std::option::Option<std::string::String>,
+        pub insertion_point: ::core::option::Option<alloc::string::String>,
         /// The file contents.
         #[prost(string, optional, tag="15")]
-        pub content: ::std::option::Option<std::string::String>,
+        pub content: ::core::option::Option<alloc::string::String>,
     }
 }

prost-types/src/lib.rs

@@ -9,8 +9,15 @@
 //!
 //! [1]: https://developers.google.com/protocol-buffers/docs/reference/google.protobuf
 
-use std::i32;
-use std::i64;
+#![no_std]
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std;
+
+use core::i32;
+use core::i64;
+
+#[cfg(feature = "std")]
 use std::time;
 
 include!("protobuf.rs");
@@ -51,6 +58,7 @@ impl Duration {
 }
 
 /// Converts a `std::time::Duration` to a `Duration`.
+#[cfg(feature = "std")]
 impl From<time::Duration> for Duration {
     fn from(duration: time::Duration) -> Duration {
         let seconds = duration.as_secs();
@@ -74,6 +82,7 @@ impl From<time::Duration> for Duration {
 /// Converts a `Duration` to a result containing a positive (`Ok`) or negative (`Err`)
 /// `std::time::Duration`.
 // TODO: convert this to TryFrom when it's stable.
+#[cfg(feature = "std")]
 impl From<Duration> for Result<time::Duration, time::Duration> {
     fn from(mut duration: Duration) -> Result<time::Duration, time::Duration> {
         duration.normalize();
@@ -116,6 +125,7 @@ impl Timestamp {
 }
 
 /// Converts a `std::time::SystemTime` to a `Timestamp`.
+#[cfg(feature = "std")]
 impl From<time::SystemTime> for Timestamp {
     fn from(time: time::SystemTime) -> Timestamp {
         let duration = Duration::from(time.duration_since(time::UNIX_EPOCH).unwrap());
@@ -129,6 +139,7 @@ impl From<time::SystemTime> for Timestamp {
 /// Converts a `Timestamp` to a `SystemTime`, or if the timestamp falls before the Unix epoch, a
 /// duration containing the difference.
 // TODO: convert this to TryFrom when it's stable.
+#[cfg(feature = "std")]
 impl From<Timestamp> for Result<time::SystemTime, time::Duration> {
     fn from(mut timestamp: Timestamp) -> Result<time::SystemTime, time::Duration> {
         timestamp.normalize();