Implements VOLTA_FEATURE_YARN=0

crates/volta-core/src/lib.rs

@@ -1,5 +1,7 @@
 //! The main implementation crate for the core of Volta.
 
+use std::{env, ffi::OsString};
+
 mod command;
 pub mod error;
 pub mod event;
@@ -22,3 +24,8 @@ pub mod toolchain;
 pub mod version;
 
 const VOLTA_FEATURE_PNPM: &str = "VOLTA_FEATURE_PNPM";
+const VOLTA_FEATURE_YARN: &str = "VOLTA_FEATURE_YARN";
+
+pub fn is_yarn_enabled() -> bool {
+    env::var_os(VOLTA_FEATURE_YARN) != Some(OsString::from("0"))
+}

crates/volta-core/src/platform/image.rs

@@ -3,6 +3,7 @@ use std::path::PathBuf;
 
 use super::{build_path_error, Sourced};
 use crate::error::{Context, Fallible};
+use crate::is_yarn_enabled;
 use crate::layout::volta_home;
 use crate::tool::load_default_npm_version;
 use node_semver::Version;
@@ -34,9 +35,11 @@ impl Image {
             bins.push(home.pnpm_image_bin_dir(&pnpm_str));
         }
 
-        if let Some(yarn) = &self.yarn {
-            let yarn_str = yarn.value.to_string();
-            bins.push(home.yarn_image_bin_dir(&yarn_str));
+        if is_yarn_enabled() {
+            if let Some(yarn) = &self.yarn {
+                let yarn_str = yarn.value.to_string();
+                bins.push(home.yarn_image_bin_dir(&yarn_str));
+            }
         }
 
         // Add Node path to the bins last, so that any custom version of npm will be earlier in the PATH

crates/volta-core/src/platform/mod.rs

@@ -4,7 +4,7 @@ use std::fmt;
 use crate::error::{ErrorKind, Fallible};
 use crate::session::Session;
 use crate::tool::{Node, Npm, Pnpm, Yarn};
-use crate::VOLTA_FEATURE_PNPM;
+use crate::{is_yarn_enabled, VOLTA_FEATURE_PNPM};
 use node_semver::Version;
 
 mod image;
@@ -290,8 +290,10 @@ impl Platform {
             }
         }
 
-        if let Some(Sourced { value: version, .. }) = &self.yarn {
-            Yarn::new(version.clone()).ensure_fetched(session)?;
+        if is_yarn_enabled() {
+            if let Some(Sourced { value: version, .. }) = &self.yarn {
+                Yarn::new(version.clone()).ensure_fetched(session)?;
+            }
         }
 
         Ok(Image {

crates/volta-core/src/run/mod.rs

@@ -7,7 +7,7 @@ use std::process::ExitStatus;
 use crate::error::{ErrorKind, Fallible};
 use crate::platform::{CliPlatform, Image, Sourced};
 use crate::session::Session;
-use crate::VOLTA_FEATURE_PNPM;
+use crate::{is_yarn_enabled, VOLTA_FEATURE_PNPM};
 use log::debug;
 use node_semver::Version;
 
@@ -86,6 +86,7 @@ fn get_executor(
             Some("node") => node::command(args, session),
             Some("npm") => npm::command(args, session),
             Some("npx") => npx::command(args, session),
+
             Some("pnpm") => {
                 // If the pnpm feature flag variable is set, delegate to the pnpm handler
                 // If not, use the binary handler as a fallback (prior to pnpm support, installing
@@ -96,7 +97,17 @@ fn get_executor(
                     binary::command(exe, args, session)
                 }
             }
-            Some("yarn") | Some("yarnpkg") => yarn::command(args, session),
+
+            Some("yarn") | Some("yarnpkg") => {
+                println!("is_yarn_enabled: {:?}", is_yarn_enabled());
+                if is_yarn_enabled() {
+                    yarn::command(args, session)
+                } else {
+                    println!("using binary");
+                    binary::command(exe, args, session)
+                }
+            }
+
             _ => binary::command(exe, args, session),
         }
     }

crates/volta-core/src/tool/mod.rs

@@ -8,7 +8,7 @@ use crate::session::Session;
 use crate::style::{note_prefix, success_prefix, tool_version};
 use crate::sync::VoltaLock;
 use crate::version::VersionSpec;
-use crate::VOLTA_FEATURE_PNPM;
+use crate::{is_yarn_enabled, VOLTA_FEATURE_PNPM};
 use cfg_if::cfg_if;
 use log::{debug, info};
 
@@ -104,8 +104,13 @@ impl Spec {
                 }
             }
             Spec::Yarn(version) => {
-                let version = yarn::resolve(version, session)?;
-                Ok(Box::new(Yarn::new(version)))
+                if is_yarn_enabled() {
+                    let version = yarn::resolve(version, session)?;
+                    Ok(Box::new(Yarn::new(version)))
+                } else {
+                    let package = Package::new("yarn".to_owned(), version)?;
+                    Ok(Box::new(package))
+                }
             }
             // When using global package install, we allow the package manager to perform the version resolution
             Spec::Package(name, version) => {