update rust version to 1.48

[nilslice]

Not currently in this PR, but I would also like to change the compile and run entries to support using cargo, the default Rust toolchain instead of interacting with rustc directly. cargo is already available in the distribution downloaded in the setup stage.

I believe the only changes needed would be:

name = "rust"
- entrypoint = "main.rs"
+ entrypoint = "src/main.rs"
extensions = [
  "rs"
]
packages = [
  "rust-gdb"
]
setup = [
  "curl --proto '=https' --tlsv1.2 -Sf https://static.rust-lang.org/dist/rust-1.48.0-x86_64-unknown-linux-gnu.tar.gz | tar xz -C /tmp",
  "/tmp/rust-1.48.0-x86_64-unknown-linux-gnu/install.sh",
  "rm -rf /tmp/rust-1.48.0-x86_64-unknown-linux-gnu"
]

[compile]
command = [
-  "rustc",
-  "-o",
-  "main"
+  "cargo",
+  "build"
]

[run]
command = [
-  "./main"
+  "cargo",
+  "run"
]

[tests]

  [tests.hello]
  code = "fn main() {\n  println!(\"hello\");\n}"
  output = "hello\n"

I'm not sure where the repl initialization happens, but cargo new ${REPL_NAME} would be necessary, along with one additional environment variable, $USER set to the existing $REPL_OWNER value would suffice.

Thanks!

[alexapostolu]

I think the reason the CI is failing is because on the Ubuntu Bionic packages list, they only have Rust for 1.47.0+

rust-doc (1.47.0+dfsg1+llvm-1ubuntu1~18.04.1)
rust-gdb (1.47.0+dfsg1+llvm-1ubuntu1~18.04.1)
rust-lldb (1.47.0+dfsg1+llvm-1ubuntu1~18.04.1)
rust-src (1.47.0+dfsg1+llvm-1ubuntu1~18.04.1)
rustc (1.47.0+dfsg1+llvm-1ubuntu1~18.04.1 [amd64, i386], 1.24.1+dfsg1+llvm-0ubuntu2 [arm64, armhf, ppc64el, s390x]