Rust: Update version requirements and CI

The #[global_allocator] attribute is not available in versions prior to
1.28.0, the default-linker-libraries feature requires rust 1.31.0.

Adapt the CI to prevent accidental increases in Rust version by testing
against 1.31.0, beta and nightly.

.travis.yml

@@ -29,6 +29,8 @@ env:
     - HARDENING_OPTIONS="--enable-expensive-hardening"
     ## We turn off asciidoc by default, because it's slow
     - ASCIIDOC_OPTIONS="--disable-asciidoc"
+    ## Our default rust version is the minimum supported version
+    - RUST_VERSION="1.31.0"
   matrix:
     ## We want to use each build option at least once
     ##
@@ -55,9 +57,9 @@ matrix:
     # We clone our stem repo and run `make test-stem`
     - env: TEST_STEM="yes" SKIP_MAKE_CHECK="yes"
     ## Check rust online with distcheck, to make sure we remove rust products
-    - env: DISTCHECK="yes" RUST_OPTIONS="--enable-rust --enable-cargo-online-mode"
+    - env: DISTCHECK="yes" RUST_VERSION="beta" RUST_OPTIONS="--enable-rust --enable-cargo-online-mode"
     ## Check disable module dirauth with and without rust
-    - env: MODULES_OPTIONS="--disable-module-dirauth" RUST_OPTIONS="--enable-rust" TOR_RUST_DEPENDENCIES=true
+    - env: MODULES_OPTIONS="--disable-module-dirauth" RUST_VERSION="nightly" RUST_OPTIONS="--enable-rust" TOR_RUST_DEPENDENCIES=true
     - env: MODULES_OPTIONS="--disable-module-dirauth"
     ## Check NSS
     - env: NSS_OPTIONS="--enable-nss"
@@ -173,8 +175,8 @@ install:
   - if [[ "$ASCIIDOC_OPTIONS" == "" ]] && [[ "$TRAVIS_OS_NAME" == "osx" ]]; then export XML_CATALOG_FILES="/usr/local/etc/xml/catalog"; fi
   ## If we're using Rust, download rustup
   - if [[ "$RUST_OPTIONS" != "" ]]; then curl -Ssf -o rustup.sh https://sh.rustup.rs; fi
-  ## Install the nightly channels of rustc and cargo and setup our toolchain environment
-  - if [[ "$RUST_OPTIONS" != "" ]]; then sh rustup.sh -y --default-toolchain nightly; fi
+  ## Install the stable channels of rustc and cargo and setup our toolchain environment
+  - if [[ "$RUST_OPTIONS" != "" ]]; then sh rustup.sh -y --default-toolchain $RUST_VERSION; fi
   - if [[ "$RUST_OPTIONS" != "" ]]; then source $HOME/.cargo/env; fi
   ## If we're testing rust builds in offline-mode, then set up our vendored dependencies
   - if [[ "$TOR_RUST_DEPENDENCIES" == "true" ]]; then export TOR_RUST_DEPENDENCIES=$PWD/src/ext/rust/crates; fi

changes/bug31442

@@ -0,0 +1,3 @@
+  o Minor bugfixes (rust):
+    - Raise the minimum rustc version to 1.31.0, as checked by configure
+      and CI. Fixes bug 31442; bugfix on 0.3.5.4-alpha.

configure.ac

@@ -558,8 +558,8 @@ if test "x$enable_rust" = "xyes"; then
   if test "x$RUSTC_VERSION_MAJOR" = "x" -o "x$RUSTC_VERSION_MINOR" = "x"; then
     AC_MSG_ERROR([rustc version couldn't be identified])
   fi
-  if test "$RUSTC_VERSION_MAJOR" -lt 2 -a "$RUSTC_VERSION_MINOR" -lt 14; then
-    AC_MSG_ERROR([rustc must be at least version 1.14])
+  if test "$RUSTC_VERSION_MAJOR" -lt 2 -a "$RUSTC_VERSION_MINOR" -lt 31; then
+    AC_MSG_ERROR([rustc must be at least version 1.31.0])
   fi
   AC_MSG_RESULT([$RUSTC_VERSION])
 fi