Generate Rust files from protobuf files on each build

By generating sticker-tf-proto on the fly, we avoid being stuck to one
particular version of the protobuf dependency. The downside is that we
require `protoc` to be available.

.gitignore

@@ -3,6 +3,7 @@
 *~
 
 target/
+sticker-tf-proto/src/*.rs
 
 .eggs
 __pycache__

.travis.yml

@@ -1,11 +1,15 @@
-dist: xenial
+dist: bionic
 env:
   global:
   - PROJECT_NAME: sticker
 addons:
   apt:
     packages:
     - patchelf
+    - protobuf-compiler
+  homebrew:
+    packages:
+    - protobuf
 matrix:
   fast_finish: true
   include:

sticker-tf-proto/Cargo.toml

@@ -10,13 +10,7 @@ repository = "https://github.com/danieldk/sticker.git"
 license = "Apache-2.0"
 
 [dependencies]
-# This is annoying, but the generated protobuf contains
-# the version number in symbols and compilation fails when
-# this dependency is updated
-protobuf = "= 2.8.0"
+protobuf = "2"
 
 [build-dependencies]
-protoc-rust = { version = "2", optional = true }
-
-[features]
-proto-compile = [ "protoc-rust" ]
+protoc-rust = "2"

sticker-tf-proto/build.rs

@@ -1,5 +1,4 @@
 fn main() {
-    #[cfg(feature = "proto-compile")]
     protoc_rust::run(protoc_rust::Args {
         out_dir: "src",
         input: &[