Allow xtask::reformat to work without rustup

Author: Veykril

xtask/src/codegen.rs

@@ -126,27 +126,35 @@ impl fmt::Display for Location {
     }
 }
 
-fn ensure_rustfmt(sh: &Shell) {
-    let version = cmd!(sh, "rustup run stable rustfmt --version").read().unwrap_or_default();
-    if !version.contains("stable") {
-        panic!(
-            "Failed to run rustfmt from toolchain 'stable'. \
-                 Please run `rustup component add rustfmt --toolchain stable` to install it.",
-        );
-    }
-}
-
 fn reformat(text: String) -> String {
     let sh = Shell::new().unwrap();
-    ensure_rustfmt(&sh);
     let rustfmt_toml = project_root().join("rustfmt.toml");
-    let mut stdout = cmd!(
-        sh,
-        "rustup run stable rustfmt --config-path {rustfmt_toml} --config fn_single_line=true"
-    )
-    .stdin(text)
-    .read()
-    .unwrap();
+    let version = cmd!(sh, "rustup run stable rustfmt --version").read().unwrap_or_default();
+
+    // First try explicitly requesting the stable channel via rustup in case nightly is being used by default,
+    // then plain rustfmt in case rustup isn't being used to manage the compiler (e.g. when using Nix).
+    let mut stdout = if !version.contains("stable") {
+        let version = cmd!(sh, "rustfmt --version").read().unwrap_or_default();
+        if !version.contains("stable") {
+            panic!(
+                "Failed to run rustfmt from toolchain 'stable'. \
+                 Please run `rustup component add rustfmt --toolchain stable` to install it.",
+            );
+        } else {
+            cmd!(sh, "rustfmt --config-path {rustfmt_toml} --config fn_single_line=true")
+                .stdin(text)
+                .read()
+                .unwrap()
+        }
+    } else {
+        cmd!(
+            sh,
+            "rustup run stable rustfmt --config-path {rustfmt_toml} --config fn_single_line=true"
+        )
+        .stdin(text)
+        .read()
+        .unwrap()
+    };
     if !stdout.ends_with('\n') {
         stdout.push('\n');
     }