deps.sh: Update rustup or inform user of env vars

Ensure rustup is up-to-date to avoid users having a version that is too
old to support the TOML format.

If rustup was just installed, tell the user to source the new env vars
to use the correct version of the toolchain.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

scripts/deps.sh

@@ -23,7 +23,7 @@ if [[ "${ID}" =~ "debian" ]] || [[ "${ID_LIKE}" =~ "debian" ]]; then
         gcc \
         gcc-avr \
         libc-dev \
-		libhidapi-dev \
+        libhidapi-dev \
         libudev-dev \
         make \
         pkgconf \
@@ -63,7 +63,12 @@ fi
 msg "Initializing submodules"
 git submodule update --init --recursive
 
-if ! which rustup &> /dev/null; then
+RUSTUP_NEW_INSTALL=0
+if which rustup &> /dev/null; then
+    msg "Updating rustup"
+    rustup self update
+else
+    RUSTUP_NEW_INSTALL=1
     msg "Installing Rust"
     curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
       | sh -s -- -y --default-toolchain none
@@ -75,4 +80,9 @@ fi
 msg "Installing pinned Rust toolchain and components"
 rustup show
 
+if [[ $RUSTUP_NEW_INSTALL = 1 ]]; then
+    msg "rustup was just installed. Ensure cargo is on the PATH with:"
+    echo -e "    source ~/.cargo/env\n"
+fi
+
 msg "\x1B[32mSuccessfully installed dependencies"