Add no_std support to prost, prost-types & make codegen `no_std…

…` compatible This PR adds a new `std` feature to the `prost` and `prost-types` crates, which is enabled by default. Additionally, the `prost-build` and `prost-derive` crates have been updated to emit no-std compatible code. This is a breaking change for edition-2015 crates, which are likely to now require an `extern crate core;` directive when including `prost`-generated code. Co-authored-by: Chris Beck <[email protected]> Co-authored-by: Dan Burkert <[email protected]> Co-authored-by: David Flemström <[email protected]>
danburkert · May 10, 2020 · fdf9fdf · fdf9fdf
1 parent 2de785a
commit fdf9fdf
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diff --git a/.github/workflows/continuous-integration-workflow.yaml b/.github/workflows/continuous-integration-workflow.yaml
@@ -12,7 +12,8 @@ jobs:
         uses: actions-rs/toolchain@v1
         with:
             toolchain: stable
-            override: true
+            default: true
+            profile: minimal
             components: rustfmt
       - name: rustfmt
         uses: actions-rs/cargo@v1
@@ -28,7 +29,8 @@ jobs:
         uses: actions-rs/toolchain@v1
         with:
             toolchain: stable
-            override: true
+            default: true
+            profile: minimal
             components: clippy
       - name: install ninja
         uses: seanmiddleditch/gha-setup-ninja@v1
@@ -45,7 +47,7 @@ jobs:
         uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
-          args: --workspace --all-targets
+          args: --workspace --all-features --all-targets
 
   test:
     runs-on: ${{ matrix.os }}
@@ -65,8 +67,8 @@ jobs:
         uses: actions-rs/toolchain@v1
         with:
             toolchain: ${{ matrix.toolchain }}
-            override: true
-            components: rustfmt
+            default: true
+            profile: minimal
       - name: install ninja
         uses: seanmiddleditch/gha-setup-ninja@v1
       - name: cache target directory
@@ -82,3 +84,35 @@ jobs:
         with:
           command: test
           args: --workspace --all-targets
+      - name: test no-default-features
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --no-default-features
+
+  no-std:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v2
+      - name: install toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: nightly
+            default: true
+            profile: minimal
+      - name: install cargo-no-std-check
+        uses: actions-rs/cargo@v1
+        with:
+          command: install
+          args: cargo-no-std-check
+      - name: prost cargo-no-std-check
+        uses: actions-rs/cargo@v1
+        with:
+          command: no-std-check
+          args: --manifest-path Cargo.toml --no-default-features
+      - name: prost-types cargo-no-std-check
+        uses: actions-rs/cargo@v1
+        with:
+          command: no-std-check
+          args: --manifest-path prost-types/Cargo.toml --no-default-features
diff --git a/Cargo.toml b/Cargo.toml
@@ -24,6 +24,7 @@ members = [
   "protobuf",
   "tests",
   "tests-2015",
+  "tests-no-std",
 ]
 exclude = [
   # The fuzz crate can't be compiled or tested without the 'cargo fuzz' command,
@@ -36,11 +37,12 @@ exclude = [
 bench = false
 
 [features]
-default = ["prost-derive"]
+default = ["prost-derive", "std"]
 no-recursion-limit = []
+std = []
 
 [dependencies]
-bytes = "0.5"
+bytes = { version = "0.5", default-features = false }
 prost-derive = { version = "0.6.1", path = "prost-derive", optional = true }
 
 [dev-dependencies]

diff --git a/README.md b/README.md
@@ -251,6 +251,29 @@ pub struct AddressBook {
 }
 ```
 
+## Using `prost` in a `no_std` Crate
+
+`prost` is compatible with `no_std` crates. To enable `no_std` support, disable
+the `std` features in `prost` and `prost-types`:
+
+```
+[dependencies]
+prost = { version = "0.6", default-features = false, features = ["prost-derive"] }
+# Only necessary if using Protobuf well-known types:
+prost-types = { version = "0.6", default-features = false }
+```
+
+Additionally, configure `prost-buid` to output `BTreeMap`s instead of `HashMap`s
+for all Protobuf `map` fields in your `build.rs`:
+
+```rust
+let mut config = prost_build::Config::new();
+config.btree_map(&["."]);
+```
+
+When using edition 2015, it may be necessary to add an `extern crate core;`
+directive to the crate which includes `prost`-generated code.
+
 ## Serializing Existing Types
 
 `prost` uses a custom derive macro to handle encoding and decoding types, which

diff --git a/prost-build/Cargo.toml b/prost-build/Cargo.toml
@@ -10,14 +10,14 @@ description = "A Protocol Buffers implementation for the Rust Language."
 edition = "2018"
 
 [dependencies]
-bytes = "0.5"
+bytes = { version = "0.5", default-features = false }
 heck = "0.3"
 itertools = "0.8"
 log = "0.4"
 multimap = { version = "0.8", default-features = false }
 petgraph = { version = "0.5", default-features = false }
-prost = { version = "0.6.1", path = ".." }
-prost-types = { version = "0.6.1", path = "../prost-types" }
+prost = { version = "0.6.1", path = "..", default-features = false }
+prost-types = { version = "0.6.1", path = "../prost-types", default-features = false }
 tempfile = "3"
 
 [build-dependencies]

diff --git a/prost-build/src/code_generator.rs b/prost-build/src/code_generator.rs
@@ -369,12 +369,12 @@ 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("::prost::alloc::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("::prost::alloc::boxed::Box<");
         }
         self.buf.push_str(&ty);
         if boxed {
@@ -411,10 +411,10 @@ impl<'a> CodeGenerator<'a> {
             .btree_map
             .iter()
             .any(|matcher| match_ident(matcher, msg_name, Some(field.name())));
-        let (annotation_ty, rust_ty) = if btree_map {
-            ("btree_map", "BTreeMap")
+        let (annotation_ty, lib_name, rust_ty) = if btree_map {
+            ("btree_map", "::prost::alloc::collections", "BTreeMap")
         } else {
-            ("map", "HashMap")
+            ("map", "::std::collections", "HashMap")
         };
 
         let key_tag = self.field_type_tag(key);
@@ -429,8 +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 {}: {}::{}<{}, {}>,\n",
             to_snake(field.name()),
+            lib_name,
             rust_ty,
             key_ty,
             value_ty
@@ -462,7 +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
         ));
@@ -523,8 +524,11 @@ impl<'a> CodeGenerator<'a> {
             );
 
             if boxed {
-                self.buf
-                    .push_str(&format!("{}(Box<{}>),\n", to_upper_camel(field.name()), ty));
+                self.buf.push_str(&format!(
+                    "{}(::prost::alloc::boxed::Box<{}>),\n",
+                    to_upper_camel(field.name()),
+                    ty
+                ));
             } else {
                 self.buf
                     .push_str(&format!("{}({}),\n", to_upper_camel(field.name()), ty));
@@ -714,8 +718,8 @@ 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 => String::from("::prost::alloc::string::String"),
+            Type::Bytes => String::from("::prost::alloc::vec::Vec<u8>"),
             Type::Group | Type::Message => self.resolve_ident(field.type_name()),
         }
     }

diff --git a/prost-build/src/lib.rs b/prost-build/src/lib.rs
@@ -225,7 +225,7 @@ impl Config {
     /// // Match all map fields in a package.
     /// config.btree_map(&[".my_messages"]);
     ///
-    /// // Match all map fields.
+    /// // Match all map fields. Expecially useful in `no_std` contexts.
     /// config.btree_map(&["."]);
     ///
     /// // Match all map fields in a nested message.

diff --git a/prost-derive/src/field/group.rs b/prost-derive/src/field/group.rs
@@ -126,7 +126,7 @@ impl Field {
 
     pub fn clear(&self, ident: TokenStream) -> TokenStream {
         match self.label {
-            Label::Optional => quote!(#ident = ::std::option::Option::None),
+            Label::Optional => quote!(#ident = ::core::option::Option::None),
             Label::Required => quote!(#ident.clear()),
             Label::Repeated => quote!(#ident.clear()),
         }

diff --git a/prost-derive/src/field/map.rs b/prost-derive/src/field/map.rs
@@ -26,6 +26,13 @@ impl MapTy {
             MapTy::BTreeMap => Ident::new("btree_map", Span::call_site()),
         }
     }
+
+    fn lib(&self) -> TokenStream {
+        match self {
+            MapTy::HashMap => quote! { std },
+            MapTy::BTreeMap => quote! { prost::alloc },
+        }
+    }
 }
 
 fn fake_scalar(ty: scalar::Ty) -> scalar::Field {
@@ -271,11 +278,11 @@ impl Field {
             let insert_doc = format!("Inserts a key value pair into `{}`.", ident);
             Some(quote! {
                 #[doc=#get_doc]
-                pub fn #get(&self, key: #key_ref_ty) -> ::std::option::Option<#ty> {
+                pub fn #get(&self, key: #key_ref_ty) -> ::core::option::Option<#ty> {
                     self.#ident.get(#take_ref key).cloned().and_then(#ty::from_i32)
                 }
                 #[doc=#insert_doc]
-                pub fn #insert(&mut self, key: #key_ty, value: #ty) -> ::std::option::Option<#ty> {
+                pub fn #insert(&mut self, key: #key_ty, value: #ty) -> ::core::option::Option<#ty> {
                     self.#ident.insert(key, value as i32).and_then(#ty::from_i32)
                 }
             })
@@ -293,12 +300,14 @@ impl Field {
             MapTy::HashMap => Ident::new("HashMap", Span::call_site()),
             MapTy::BTreeMap => Ident::new("BTreeMap", Span::call_site()),
         };
+
         // A fake field for generating the debug wrapper
         let key_wrapper = fake_scalar(self.key_ty.clone()).debug(quote!(KeyWrapper));
         let key = self.key_ty.rust_type();
         let value_wrapper = self.value_ty.debug();
+        let libname = self.map_ty.lib();
         let fmt = quote! {
-            fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
                 #key_wrapper
                 #value_wrapper
                 let mut builder = f.debug_map();
@@ -312,17 +321,17 @@ impl Field {
             ValueTy::Scalar(ty) => {
                 let value = ty.rust_type();
                 quote! {
-                    struct #wrapper_name<'a>(&'a ::std::collections::#type_name<#key, #value>);
-                    impl<'a> ::std::fmt::Debug for #wrapper_name<'a> {
+                    struct #wrapper_name<'a>(&'a ::#libname::collections::#type_name<#key, #value>);
+                    impl<'a> ::core::fmt::Debug for #wrapper_name<'a> {
                         #fmt
                     }
                 }
             }
             ValueTy::Message => quote! {
-                struct #wrapper_name<'a, V: 'a>(&'a ::std::collections::#type_name<#key, V>);
-                impl<'a, V> ::std::fmt::Debug for #wrapper_name<'a, V>
+                struct #wrapper_name<'a, V: 'a>(&'a ::#libname::collections::#type_name<#key, V>);
+                impl<'a, V> ::core::fmt::Debug for #wrapper_name<'a, V>
                 where
-                    V: ::std::fmt::Debug + 'a,
+                    V: ::core::fmt::Debug + 'a,
                 {
                     #fmt
                 }

diff --git a/prost-derive/src/field/message.rs b/prost-derive/src/field/message.rs
@@ -126,7 +126,7 @@ impl Field {
 
     pub fn clear(&self, ident: TokenStream) -> TokenStream {
         match self.label {
-            Label::Optional => quote!(#ident = ::std::option::Option::None),
+            Label::Optional => quote!(#ident = ::core::option::Option::None),
             Label::Required => quote!(#ident.clear()),
             Label::Repeated => quote!(#ident.clear()),
         }

diff --git a/prost-derive/src/field/mod.rs b/prost-derive/src/field/mod.rs
@@ -135,7 +135,7 @@ impl Field {
     pub fn default(&self) -> TokenStream {
         match *self {
             Field::Scalar(ref scalar) => scalar.default(),
-            _ => quote!(::std::default::Default::default()),
+            _ => quote!(::core::default::Default::default()),
         }
     }
 

diff --git a/prost-derive/src/field/oneof.rs b/prost-derive/src/field/oneof.rs
@@ -94,6 +94,6 @@ impl Field {
     }
 
     pub fn clear(&self, ident: TokenStream) -> TokenStream {
-        quote!(#ident = ::std::option::Option::None)
+        quote!(#ident = ::core::option::Option::None)
     }
 }