add SandboxBuilder image override

src/build.rs

@@ -175,7 +175,8 @@ impl BuildDirectory {
         self.workspace.builds_dir().join(&self.name)
     }
 
-    fn source_dir(&self) -> PathBuf {
+    /// Get the path to the source code on the host machine (outside the sandbox).
+    pub fn source_dir(&self) -> PathBuf {
         self.build_dir().join("source")
     }
 

src/cmd/sandbox.rs

@@ -8,6 +8,7 @@ use std::path::{Path, PathBuf};
 use std::time::Duration;
 
 /// The Docker image used for sandboxing.
+#[derive(Clone)]
 pub struct SandboxImage {
     name: String,
 }
@@ -146,6 +147,7 @@ pub struct SandboxBuilder {
     user: Option<String>,
     cmd: Vec<String>,
     enable_networking: bool,
+    image: Option<SandboxImage>,
 }
 
 impl SandboxBuilder {
@@ -160,6 +162,7 @@ impl SandboxBuilder {
             user: None,
             cmd: Vec::new(),
             enable_networking: true,
+            image: None,
         }
     }
 
@@ -203,6 +206,14 @@ impl SandboxBuilder {
         self
     }
 
+    /// Override the image used for this sandbox.
+    ///
+    /// By default rustwide will use the image from the `Workspace`.
+    pub fn image(mut self, image: SandboxImage) -> Self {
+        self.image = Some(image);
+        self
+    }
+
     pub(super) fn env<S1: Into<String>, S2: Into<String>>(mut self, key: S1, value: S2) -> Self {
         self.env.push((key.into(), value.into()));
         self
@@ -274,7 +285,11 @@ impl SandboxBuilder {
             args.push("--isolation=process".into());
         }
 
-        args.push(workspace.sandbox_image().name.clone());
+        if let Some(image) = self.image {
+            args.push(image.name);
+        } else {
+            args.push(workspace.sandbox_image().name.clone());
+        }
 
         for arg in self.cmd {
             args.push(arg);