ci: check for common Rust mistakes via Clippy

Introduce a CI check that uses Clippy to perform checks for common
mistakes and suggested code improvements. Clippy is the official static
analyser of the Rust project and thus the de-facto standard.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

ci/install-dependencies.sh

@@ -129,7 +129,7 @@ StaticAnalysis)
 RustAnalysis)
 	sudo apt-get -q -y install rustup
 	rustup default stable
-	rustup component add rustfmt
+	rustup component add clippy rustfmt
 	;;
 sparse)
 	sudo apt-get -q -y install libssl-dev libcurl4-openssl-dev \

ci/run-rust-checks.sh

@@ -9,4 +9,9 @@ then
 	RET=1
 fi
 
+if ! group "Check for common Rust mistakes" cargo clippy --all-targets --all-features -- -Dwarnings
+then
+	RET=1
+fi
+
 exit $RET