Upgrade to Rust 1.42 (#8836)

* Upgrade to Rust 1.42

* deref

* parens

Co-authored-by: Trent Nelson <trent@solana.com>

ci/docker-rust-nightly/Dockerfile

@@ -1,4 +1,4 @@
-FROM solanalabs/rust:1.41.1
+FROM solanalabs/rust:1.42.0
 ARG date
 
 RUN set -x \

ci/docker-rust-nightly/README.md

@@ -15,6 +15,8 @@ To update the pinned version:
 1. Run `ci/docker-rust-nightly/build.sh` to rebuild the nightly image locally,
    or potentially `ci/docker-rust-nightly/build.sh YYYY-MM-DD` if there's a
    specific YYYY-MM-DD that is desired (default is today's build).
+   Check https://rust-lang.github.io/rustup-components-history/ for build
+   status
 1. Update `ci/rust-version.sh` to reflect the new nightly `YYY-MM-DD`
 1. Run `SOLANA_DOCKER_RUN_NOSETUID=1 ci/docker-run.sh --nopull solanalabs/rust-nightly:YYYY-MM-DD ci/test-coverage.sh`
    to confirm the new nightly image builds.  Fix any issues as needed

ci/docker-rust/Dockerfile

@@ -1,6 +1,6 @@
 # Note: when the rust version is changed also modify
 # ci/rust-version.sh to pick up the new image tag
-FROM rust:1.41.1
+FROM rust:1.42.0
 
 # Add Google Protocol Buffers for Libra's metrics library.
 ENV PROTOC_VERSION 3.8.0

ci/rust-version.sh

@@ -16,13 +16,13 @@
 if [[ -n $RUST_STABLE_VERSION ]]; then
   stable_version="$RUST_STABLE_VERSION"
 else
-  stable_version=1.41.1
+  stable_version=1.42.0
 fi
 
 if [[ -n $RUST_NIGHTLY_VERSION ]]; then
   nightly_version="$RUST_NIGHTLY_VERSION"
 else
-  nightly_version=2020-02-27
+  nightly_version=2020-03-12
 fi