Codegen: option to use BTreeMap as map representation

As of now, protobuf maps are represented with
[std::collections::HashMap](https://doc.rust-lang.org/stable/std/collections/struct.HashMap.html),
which serves as a robust default. In rarer instances, opting for a
different implementation, such as BTreeMap, might be desirable,
e.g. for deterministic serialization.

This change

* adds `btreemaps` codegen option to generate
  [std::collections::BTreeMap](https://doc.rust-lang.org/std/collections/struct.BTreeMap.html)
  for maps representation.

.github/workflows/ci.yml

@@ -8,8 +8,14 @@ jobs:
     linux-stable-default-features:
         name: linux stable (default features)
         runs-on: ubuntu-latest
+        strategy:
+            matrix:
+                map_representation:
+                    - btreemap
+                    - hashmap
         env:
             RUST_BACKTRACE: 1
+            MAP_REPRESENTATION: ${{ matrix.map_representation }}
         steps:
             - name: Checkout sources
               uses: actions/checkout@v2
@@ -53,8 +59,14 @@ jobs:
     linux-beta-default-features:
         name: linux beta (default features)
         runs-on: ubuntu-latest
+        strategy:
+            matrix:
+                map_representation:
+                    - btreemap
+                    - hashmap
         env:
             RUST_BACKTRACE: 1
+            MAP_REPRESENTATION: ${{ matrix.map_representation }}
         steps:
             - name: Checkout sources
               uses: actions/checkout@v2
@@ -98,8 +110,14 @@ jobs:
     linux-stable-with-bytes:
         name: linux stable (with-bytes)
         runs-on: ubuntu-latest
+        strategy:
+            matrix:
+                map_representation:
+                    - btreemap
+                    - hashmap
         env:
             RUST_BACKTRACE: 1
+            MAP_REPRESENTATION: ${{ matrix.map_representation }}
         steps:
             - name: Checkout sources
               uses: actions/checkout@v2
@@ -140,8 +158,14 @@ jobs:
     linux-nightly-all-features:
         name: linux nightly (all features)
         runs-on: ubuntu-latest
+        strategy:
+            matrix:
+                map_representation:
+                    - btreemap
+                    - hashmap
         env:
             RUST_BACKTRACE: 1
+            MAP_REPRESENTATION: ${{ matrix.map_representation }}
         steps:
             - name: Checkout sources
               uses: actions/checkout@v2
@@ -183,8 +207,14 @@ jobs:
     windows-stable-default-features:
         name: windows stable (default features)
         runs-on: windows-latest
+        strategy:
+            matrix:
+                map_representation:
+                    - btreemap
+                    - hashmap
         env:
             RUST_BACKTRACE: 1
+            MAP_REPRESENTATION: ${{ matrix.map_representation }}
             VCPKGRS_DYNAMIC: 1
         steps:
             - name: Checkout sources

ci-gen/src/ghwf.rs

@@ -121,6 +121,7 @@ pub struct Job {
     pub id: String,
     pub name: String,
     pub runs_on: Env,
+    pub strategy: Option<Strategy>,
     pub steps: Vec<Step>,
     pub timeout_minutes: Option<u64>,
     pub env: Vec<(String, String)>,
@@ -141,6 +142,9 @@ impl Into<(String, Yaml)> for Job {
             ("name", Yaml::string(self.name)),
             ("runs-on", Yaml::string(format!("{}", self.runs_on))),
         ];
+        if let Some(strategy) = self.strategy {
+            entries.push(("strategy", strategy.into()));
+        }
         if let Some(timeout_minutes) = self.timeout_minutes {
             entries.push((
                 "timeout-minutes",
@@ -154,3 +158,26 @@ impl Into<(String, Yaml)> for Job {
         (self.id, Yaml::map(entries))
     }
 }
+
+pub struct Strategy {
+    pub matrix: Matrix,
+}
+
+impl Into<Yaml> for Strategy {
+    fn into(self) -> Yaml {
+        Yaml::map(vec![("matrix".to_owned(), self.matrix)])
+    }
+}
+
+pub struct Matrix {
+    pub map_representation: Vec<String>,
+}
+
+impl Into<Yaml> for Matrix {
+    fn into(self) -> Yaml {
+        Yaml::map(vec![(
+            "map_representation".to_owned(),
+            Yaml::list(self.map_representation),
+        )])
+    }
+}

ci-gen/src/main.rs

@@ -16,7 +16,9 @@ use crate::actions::RustToolchain;
 use crate::cargo_sync_readme::cargo_sync_readme_job;
 use crate::ghwf::Env;
 use crate::ghwf::Job;
+use crate::ghwf::Matrix;
 use crate::ghwf::Step;
+use crate::ghwf::Strategy;
 use crate::yaml::Yaml;
 use crate::yaml::YamlWriter;
 
@@ -155,7 +157,13 @@ fn job(channel: RustToolchain, os: Os, features: Features) -> Job {
         }
     }
 
-    let mut env = vec![("RUST_BACKTRACE".to_owned(), "1".to_owned())];
+    let mut env = vec![
+        ("RUST_BACKTRACE".to_owned(), "1".to_owned()),
+        (
+            "MAP_REPRESENTATION".to_owned(),
+            "${{ matrix.map_representation }}".to_owned(),
+        ),
+    ];
     if os == WINDOWS {
         env.push(("VCPKGRS_DYNAMIC".to_owned(), "1".to_owned()));
     };
@@ -167,6 +175,11 @@ fn job(channel: RustToolchain, os: Os, features: Features) -> Job {
         runs_on: os.ghwf.to_owned(),
         steps,
         env,
+        strategy: Some(Strategy {
+            matrix: Matrix {
+                map_representation: vec!["btreemap".to_owned(), "hashmap".to_owned()],
+            },
+        }),
         ..Default::default()
     }
 }

protobuf-codegen/src/customize/mod.rs

@@ -109,6 +109,8 @@ pub struct Customize {
     /// Used internally to generate protos bundled in protobuf crate
     /// like `descriptor.proto`
     pub(crate) inside_protobuf: Option<bool>,
+    /// When true, protobuf maps are represented with `std::collections::BTreeMap`
+    pub(crate) btreemaps: Option<bool>,
 }
 
 #[derive(Debug, thiserror::Error)]
@@ -171,6 +173,14 @@ impl Customize {
         self
     }
 
+    /// Use btreemaps for maps representation
+    pub fn btreemaps(self, use_btreemaps: bool) -> Self {
+        Self {
+            btreemaps: Some(use_btreemaps),
+            ..self
+        }
+    }
+
     /// Update fields of self with fields defined in other customize
     pub fn update_with(&mut self, that: &Customize) {
         if let Some(v) = &that.before {
@@ -197,6 +207,9 @@ impl Customize {
         if let Some(v) = that.inside_protobuf {
             self.inside_protobuf = Some(v);
         }
+        if let Some(v) = that.btreemaps {
+            self.btreemaps = Some(v);
+        }
     }
 
     /// Update unset fields of self with fields from other customize

protobuf-codegen/src/customize/rustproto_proto.rs

@@ -15,6 +15,7 @@ pub(crate) fn customize_from_rustproto_for_message(source: &MessageOptions) -> C
     let lite_runtime = None;
     let gen_mod_rs = None;
     let inside_protobuf = None;
+    let btreemaps = None;
     Customize {
         before,
         generate_accessors,
@@ -24,6 +25,7 @@ pub(crate) fn customize_from_rustproto_for_message(source: &MessageOptions) -> C
         lite_runtime,
         gen_mod_rs,
         inside_protobuf,
+        btreemaps,
     }
 }
 
@@ -40,6 +42,7 @@ pub(crate) fn customize_from_rustproto_for_field(source: &FieldOptions) -> Custo
     let lite_runtime = None;
     let gen_mod_rs = None;
     let inside_protobuf = None;
+    let btreemaps = None;
     Customize {
         before,
         generate_accessors,
@@ -49,6 +52,7 @@ pub(crate) fn customize_from_rustproto_for_field(source: &FieldOptions) -> Custo
         lite_runtime,
         gen_mod_rs,
         inside_protobuf,
+        btreemaps,
     }
 }
 
@@ -61,6 +65,7 @@ pub(crate) fn customize_from_rustproto_for_file(source: &FileOptions) -> Customi
     let lite_runtime = rustproto::exts::lite_runtime_all.get(source);
     let gen_mod_rs = None;
     let inside_protobuf = None;
+    let btreemaps = None;
     Customize {
         before,
         generate_accessors,
@@ -70,5 +75,6 @@ pub(crate) fn customize_from_rustproto_for_file(source: &FileOptions) -> Customi
         lite_runtime,
         inside_protobuf,
         gen_mod_rs,
+        btreemaps,
     }
 }

protobuf-codegen/src/gen/field/accessor.rs

@@ -66,7 +66,7 @@ impl FieldGen<'_> {
         let MapField { .. } = map_field;
         AccessorFn {
             name: "make_map_simpler_accessor".to_owned(),
-            type_params: vec![format!("_"), format!("_")],
+            type_params: vec![format!("_")],
             callback_params: self.make_accessor_fns_lambda(),
         }
     }

protobuf-codegen/src/gen/field/mod.rs

@@ -276,7 +276,7 @@ impl<'a> FieldGen<'a> {
             FieldKind::Repeated(ref repeated) => repeated.rust_type(reference),
             FieldKind::Map(MapField {
                 ref key, ref value, ..
-            }) => RustType::HashMap(
+            }) => RustType::Map(
                 Box::new(key.rust_storage_elem_type(reference)),
                 Box::new(value.rust_storage_elem_type(reference)),
             ),

protobuf-codegen/src/gen/rust_types_values.rs

@@ -33,7 +33,7 @@ pub(crate) enum RustType {
     Float(u32),
     Bool,
     Vec(Box<RustType>),
-    HashMap(Box<RustType>, Box<RustType>),
+    Map(Box<RustType>, Box<RustType>),
     String,
     // [T], not &[T]
     Slice(Box<RustType>),
@@ -70,11 +70,19 @@ impl RustType {
             RustType::Float(bits) => format!("f{}", bits),
             RustType::Bool => format!("bool"),
             RustType::Vec(ref param) => format!("::std::vec::Vec<{}>", param.to_code(customize)),
-            RustType::HashMap(ref key, ref value) => format!(
-                "::std::collections::HashMap<{}, {}>",
-                key.to_code(customize),
-                value.to_code(customize)
-            ),
+            RustType::Map(ref key, ref value) => {
+                let ty = if let Some(true) = customize.btreemaps {
+                    "::std::collections::BTreeMap"
+                } else {
+                    "::std::collections::HashMap"
+                };
+                format!(
+                    "{}<{}, {}>",
+                    ty,
+                    key.to_code(customize),
+                    value.to_code(customize)
+                )
+            }
             RustType::String => format!("::std::string::String"),
             RustType::Slice(ref param) => format!("[{}]", param.to_code(customize)),
             RustType::Str => format!("str"),
@@ -220,7 +228,14 @@ impl RustType {
             RustType::Float(..) => "0.".to_string(),
             RustType::Bool => "false".to_string(),
             RustType::Vec(..) => EXPR_VEC_NEW.to_string(),
-            RustType::HashMap(..) => "::std::collections::HashMap::new()".to_string(),
+            RustType::Map(..) => {
+                let ty = if let Some(true) = customize.btreemaps {
+                    "::std::collections::BTreeMap"
+                } else {
+                    "::std::collections::HashMap"
+                };
+                format!("{}::new()", ty)
+            }
             RustType::String => "::std::string::String::new()".to_string(),
             RustType::Bytes => "::bytes::Bytes::new()".to_string(),
             RustType::Chars => format!("{}::Chars::new()", protobuf_crate_path(customize)),
@@ -266,7 +281,7 @@ impl RustType {
             | RustType::Chars
             | RustType::String
             | RustType::MessageField(..)
-            | RustType::HashMap(..) => format!("{}.clear()", v),
+            | RustType::Map(..) => format!("{}.clear()", v),
             RustType::Bool
             | RustType::Float(..)
             | RustType::Int(..)