Merge #1057

1057: suggest that buildx needs to be available r=Alexhuszagh a=Emilgardis

touches on #1055

```
❯ cross build --target x86_64-unknown-linux-gnu
unknown flag: --label
See 'docker buildx build --help'.
Error: 
   0: could not run container
   1: when building custom image
   2: when pre-building
   3: `docker buildx build --platform linux/amd64 --labela 'org.cross-rs.for-cross-target=x86_64-unknown-linux-gnu' --label 'org.cross-rs.runs-with=x86_64-unknown-linux-gnu' --label 'org.cross-rs.workspace_root=/Users/emil/workspace/cross' --tag localhost/cross-rs/cross-custom-cross:x86_64-unknown-linux-gnu-b0dac-pre-build --build-arg 'CROSS_CMD=hello world' --build-arg 'CROSS_DEB_ARCH=amd64' --file /Users/emil/workspace/cross/target/x86_64-unknown-linux-gnu/Dockerfile.x86_64-unknown-linux-gnu-custom --output 'type=docker' /Users/emil/workspace/cross` failed with exit status: 125

Warning: call to docker failed
Suggestion: is `buildx` available for the container engine?
Note: disable the `buildkit` dependency optionally with `CROSS_CONTAINER_ENGINE_NO_BUILDKIT=1`
Note: CROSS_CMD=hello world
```

Co-authored-by: Emil Gardström <[email protected]>

Author: bors[bot]

src/bin/commands/images.rs

@@ -276,7 +276,7 @@ pub fn list_images(
             map.get_mut(&target).expect("map must have key").push(image);
         }
     }
-    let mut keys: Vec<&str> = map.iter().map(|(k, _)| k.as_ref()).collect();
+    let mut keys: Vec<&str> = map.keys().map(|k| k.as_ref()).collect();
     keys.sort_unstable();
 
     let print_string =

src/docker/custom.rs

@@ -163,7 +163,32 @@ impl<'a> Dockerfile<'a> {
             docker_build.arg(paths.host_root());
         }
 
-        docker_build.run(msg_info, true)?;
+        let mut res = docker_build.run(msg_info, true).with_warning(|| {
+            format!(
+                "call to {} failed",
+                options
+                    .engine
+                    .path
+                    .file_name()
+                    .and_then(|s| s.to_str())
+                    .map_or_else(|| "container engine", |s| s)
+            )
+        });
+
+        // FIXME: Inspect the error message, while still inheriting stdout on verbose mode to
+        // conditionally apply this suggestion and note. This could then inspect if a help string is emitted,
+        // if the daemon is not running, etc.
+        if docker::Engine::has_buildkit() {
+            res = res
+                .suggestion("is `buildx` available for the container engine?")
+                .with_note(|| {
+                    format!(
+                        "disable the `buildkit` dependency optionally with `{}=1`",
+                        docker::Engine::CROSS_CONTAINER_ENGINE_NO_BUILDKIT_ENV
+                    )
+                });
+        }
+        res?;
         Ok(image_name)
     }
 

src/docker/engine.rs

@@ -69,6 +69,8 @@ pub struct Engine {
 }
 
 impl Engine {
+    pub const CROSS_CONTAINER_ENGINE_NO_BUILDKIT_ENV: &'static str =
+        "CROSS_CONTAINER_ENGINE_NO_BUILDKIT";
     pub fn new(
         in_docker: Option<bool>,
         is_remote: Option<bool>,
@@ -135,7 +137,7 @@ impl Engine {
 
     #[must_use]
     pub fn has_buildkit() -> bool {
-        !env::var("CROSS_CONTAINER_ENGINE_NO_BUILDKIT")
+        !env::var(Self::CROSS_CONTAINER_ENGINE_NO_BUILDKIT_ENV)
             .map(|x| bool_from_envvar(&x))
             .unwrap_or_default()
     }