Merge #1748

1748: Add format test to CI r=rtzoeller a=costinsin

To enforce uniformity for all PRs, the CI checks if the code
is formatted right using `cargo fmt` tool.

Results after implementing the format test in CicleCI, but before fixing the format errors: https://cirrus-ci.com/build/4684991404703744
Results after fixing the format errors: https://cirrus-ci.com/build/5423803479097344

Solves #770 

Co-authored-by: Costin-Robert Sin <sin.costinrobert@gmail.com>

Author: bors[bot]

.cirrus.yml

@@ -320,3 +320,11 @@ task:
   check_script:
     - cargo check
   before_cache_script: rm -rf $CARGO_HOME/registry/index
+
+# Tasks that checks if the code is formatted right using `cargo fmt` tool
+task:
+  name: Rust Formatter
+  container:
+    image: rust:latest
+  setup_script: rustup +$TOOLCHAIN component add rustfmt
+  test_script: $TOOL +$TOOLCHAIN fmt --all -- --check

bors.toml

@@ -33,6 +33,7 @@ status = [
   "OpenBSD x86_64",
   "Redox x86_64",
   "Rust Stable",
+  "Rust Formatter",
   "iOS aarch64",
   "iOS x86_64",
   "Illumos",

rustfmt.toml

@@ -0,0 +1 @@
+max_width = 80