bump xargo version, and tweak xargo caching

.github/workflows/ci.yml

@@ -57,14 +57,15 @@ jobs:
             # contains package information of crates installed via `cargo install`.
             ~/.cargo/.crates.toml
             ~/.cargo/.crates2.json
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}-xargo0.3.25
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock', 'cargo-miri/version.rs') }}
           restore-keys: ${{ runner.os }}-cargo
 
       - name: Install rustup-toolchain-install-master and xargo
         shell: bash
         run: |
           cargo install rustup-toolchain-install-master
-          cargo install xargo
+          # Only install xargo if we don't have it cached
+          if ! which xargo; then cargo install xargo; fi
 
       - name: Install "master" toolchain
         shell: bash

cargo-miri/bin.rs

@@ -1,3 +1,5 @@
+mod version;
+
 use std::env;
 use std::ffi::{OsStr, OsString};
 use std::fmt::Write as _;
@@ -9,10 +11,9 @@ use std::path::{Path, PathBuf};
 use std::process::{self, Command};
 
 use serde::{Deserialize, Serialize};
-
 use rustc_version::VersionMeta;
 
-const XARGO_MIN_VERSION: (u32, u32, u32) = (0, 3, 23);
+use version::*;
 
 const CARGO_MIRI_HELP: &str = r#"Runs binary crates and tests in Miri
 

cargo-miri/version.rs

@@ -0,0 +1,2 @@
+// We put this in a separate file so that it can be hashed for GHA caching.
+pub const XARGO_MIN_VERSION: (u32, u32, u32) = (0, 3, 26);