add --without-cargo flag to change default cargo install behavior

Author: chrissimpkins

src/main.rs

@@ -151,6 +151,12 @@ struct Opts {
         parse(from_os_str)
     )]
     script: Option<PathBuf>,
+
+    #[structopt(
+        long = "without-cargo",
+        help = "Do not install cargo [default: install cargo]"
+    )]
+    without_cargo: bool,
 }
 
 pub type GitDate = Date<Utc>;

src/toolchains.rs

@@ -231,20 +231,21 @@ impl Toolchain {
             .map_err(InstallError::Download)?;
         }
 
-        // download nightly cargo by default
-        // this behavior was changed from an
-        // optional feature with the `--with-cargo`
-        // flag as of v0.6.0
+        // download cargo by default
+        // deactivate with the `--without-cargo` flag
+        // this default behavior was changed as of v0.6.0
         // see: https://github.com/rust-lang/cargo-bisect-rustc/issues/81
-        let filename = format!("cargo-nightly-{}", self.host);
-        download_tarball(
-            &client,
-            &format!("cargo for {}", self.host),
-            &format!("{}/{}/{}.tar", dl_params.url_prefix, location, filename,),
-            Some(&PathBuf::from(&filename).join("cargo")),
-            tmpdir.path(),
-        )
-        .map_err(InstallError::Download)?;
+        if !dl_params.without_cargo {
+            let filename = format!("cargo-nightly-{}", self.host);
+            download_tarball(
+                &client,
+                &format!("cargo for {}", self.host),
+                &format!("{}/{}/{}.tar", dl_params.url_prefix, location, filename,),
+                Some(&PathBuf::from(&filename).join("cargo")),
+                tmpdir.path(),
+            )
+            .map_err(InstallError::Download)?;
+        }
 
         if dl_params.install_src {
             let filename = "rust-src-nightly";
@@ -411,6 +412,7 @@ pub(crate) struct DownloadParams {
     tmp_dir: PathBuf,
     install_dir: PathBuf,
     install_src: bool,
+    without_cargo: bool,
     force_install: bool,
 }
 
@@ -435,6 +437,7 @@ impl DownloadParams {
             tmp_dir: cfg.rustup_tmp_path.clone(),
             install_dir: cfg.toolchains_path.clone(),
             install_src: cfg.args.with_src,
+            without_cargo: cfg.args.without_cargo,
             force_install: cfg.args.force_install,
         }
     }