Fix docker_read_mount_paths to support podman.

Used to hard-code a search for docker, which is now removed to use the
path of the located engine. Also adds the `CROSS_CONTAINER_IN_CONTAINER`
environment variables, which overrides the `CROSS_DOCKER_IN_DOCKER`
variable.

README.md

@@ -144,15 +144,15 @@ container used for cross compilation. This includes the original project directo
 well as the root path of the parent container to give access to the rust build
 tools.
 
-To inform `cross` that it is running inside a container set `CROSS_DOCKER_IN_DOCKER=true`.
+To inform `cross` that it is running inside a container set `CROSS_CONTAINER_IN_CONTAINER=true`.
 
 A development or CI container can be created like this:
 
 ```
 FROM rust:1
 
-# set CROSS_DOCKER_IN_DOCKER to inform `cross` that it is executed from within a container
-ENV CROSS_DOCKER_IN_DOCKER=true
+# set CROSS_CONTAINER_IN_CONTAINER to inform `cross` that it is executed from within a container
+ENV CROSS_CONTAINER_IN_CONTAINER=true
 
 # install `cross`
 RUN cargo install cross

src/cli.rs

@@ -133,9 +133,20 @@ pub fn parse(target_list: &TargetList) -> Result<Args> {
         }
     }
 
-    let docker_in_docker = env::var("CROSS_DOCKER_IN_DOCKER")
-        .map(|s| bool_from_envvar(&s))
-        .unwrap_or_default();
+    let docker_in_docker = if let Ok(value) = env::var("CROSS_CONTAINER_IN_CONTAINER") {
+        if env::var("CROSS_DOCKER_IN_DOCKER").is_ok() {
+            eprintln!(
+                "Warning: using both `CROSS_CONTAINER_IN_CONTAINER` and `CROSS_DOCKER_IN_DOCKER`."
+            );
+        }
+        bool_from_envvar(&value)
+    } else if let Ok(value) = env::var("CROSS_DOCKER_IN_DOCKER") {
+        // FIXME: remove this when we deprecate CROSS_DOCKER_IN_DOCKER.
+        bool_from_envvar(&value)
+    } else {
+        false
+    };
+
     let enable_doctests = env::var("CROSS_UNSTABLE_ENABLE_DOCTESTS")
         .map(|s| bool_from_envvar(&s))
         .unwrap_or_default();

src/docker.rs

@@ -131,8 +131,13 @@ pub fn run(
     docker_in_docker: bool,
     cwd: &Path,
 ) -> Result<ExitStatus> {
+    let engine = get_container_engine()
+        .map_err(|_| eyre::eyre!("no container engine found"))
+        .with_suggestion(|| "is docker or podman installed?")?;
+    let engine_type = get_engine_type(&engine, verbose)?;
+
     let mount_finder = if docker_in_docker {
-        MountFinder::new(docker_read_mount_paths()?)
+        MountFinder::new(docker_read_mount_paths(&engine)?)
     } else {
         MountFinder::default()
     };
@@ -193,11 +198,6 @@ pub fn run(
 
     let runner = config.runner(target)?;
 
-    let engine = get_container_engine()
-        .map_err(|_| eyre::eyre!("no container engine found"))
-        .with_suggestion(|| "is docker or podman installed?")?;
-    let engine_type = get_engine_type(&engine, verbose)?;
-
     let mut docker = docker_command(&engine, "run")?;
 
     for ref var in config.env_passthrough(target)? {
@@ -408,13 +408,11 @@ fn wslpath(path: &Path, verbose: bool) -> Result<PathBuf> {
         .map(|s| s.trim().into())
 }
 
-fn docker_read_mount_paths() -> Result<Vec<MountDetail>> {
+fn docker_read_mount_paths(engine: &Path) -> Result<Vec<MountDetail>> {
     let hostname = env::var("HOSTNAME").wrap_err("HOSTNAME environment variable not found")?;
 
-    let docker_path = which::which(DOCKER)?;
     let mut docker: Command = {
-        let mut command = Command::new(docker_path);
-        command.arg("inspect");
+        let mut command = docker_command(engine, "inspect")?;
         command.arg(hostname);
         command
     };