Merge cross-rs#312

312: Fall back to using `cargo` on the host when no image is found. r=reitermarkus a=reitermarkus



Co-authored-by: Markus Reiter <me@reitermark.us>

src/docker.rs

@@ -171,7 +171,7 @@ pub fn run(target: &Target,
         .run_and_get_status(verbose)
 }
 
-fn image(toml: Option<&Toml>, target: &Target) -> Result<String> {
+pub fn image(toml: Option<&Toml>, target: &Target) -> Result<String> {
     if let Some(toml) = toml {
         if let Some(image) = toml.image(target)?.map(|s| s.to_owned()) {
             return Ok(image)
@@ -181,8 +181,8 @@ fn image(toml: Option<&Toml>, target: &Target) -> Result<String> {
     let triple = target.triple();
 
     if !DOCKER_IMAGES.contains(&triple) {
-        bail!("cross does not provide docker image for {} target, \
-               specify a custom image in Cross.toml", triple);
+        bail!("`cross` does not provide a Docker image for target {}, \
+               specify a custom image in `Cross.toml`.", triple);
     }
 
     let version = env!("CARGO_PKG_VERSION");

src/main.rs

@@ -277,7 +277,15 @@ fn run() -> Result<ExitStatus> {
 
             let needs_interpreter = args.subcommand.map(|sc| sc.needs_interpreter()).unwrap_or(false);
 
-            if target.needs_docker() &&
+            let image_exists = match docker::image(toml.as_ref(), &target) {
+                Ok(_) => true,
+                Err(err) => {
+                    eprintln!("Warning: {} Falling back to `cargo` on the host.", err);
+                    false
+                },
+            };
+
+            if image_exists && target.needs_docker() &&
                args.subcommand.map(|sc| sc.needs_docker()).unwrap_or(false) {
                 if version_meta.needs_interpreter() &&
                     needs_interpreter &&