remove provide-image, replace with arg

README.md

@@ -134,7 +134,14 @@ RUN dpkg --add-architecture arm64 && \
     apt-get install --assume-yes libfoo:arm64
 ```
 
-If you want cross to provide the `FROM` instruction, use `target.{{TARGET}}.dockerfile.provide-base`.
+If you want cross to provide the `FROM` instruction, you can do the following
+
+``` Dockerfile
+ARG CROSS_BASE_IMAGE
+FROM $CROSS_BASE_IMAGE
+
+RUN ...
+```
 
 #### Pre-build hook
 

docs/cross_toml.md

@@ -52,5 +52,4 @@ passthrough = ["IMPORTANT_ENV_VARIABLES"]
 file = "./Dockerfile"
 context = "."
 build-args = { ARG1 = "foo" }
-provide-base = false # tell cross to insert a `FROM` instruction
 ```

src/config.rs

@@ -64,11 +64,6 @@ impl Environment {
         self.get_target_var(target, "DOCKERFILE")
     }
 
-    fn dockerfile_provide_base(&self, target: &Target) -> Option<bool> {
-        self.get_target_var(target, "DOCKERFILE_PROVIDE_BASE")
-            .map(|s| bool_from_envvar(&s))
-    }
-
     fn dockerfile_context(&self, target: &Target) -> Option<String> {
         self.get_target_var(target, "DOCKERFILE_CONTEXT")
     }
@@ -248,14 +243,6 @@ impl Config {
         self.string_from_config(target, Environment::dockerfile, CrossToml::dockerfile)
     }
 
-    pub fn dockerfile_provide_base(&self, target: &Target) -> Option<bool> {
-        self.bool_from_config(
-            target,
-            |s, t| (None, s.dockerfile_provide_base(t)),
-            |s, t| (None, s.dockerfile_provide_base(t)),
-        )
-    }
-
     pub fn dockerfile_context(&self, target: &Target) -> Result<Option<String>> {
         self.string_from_config(
             target,

src/cross_toml.rs

@@ -45,8 +45,6 @@ pub struct CrossTargetConfig {
 #[serde(rename_all = "kebab-case")]
 pub struct CrossTargetDockerfileConfig {
     file: String,
-    #[serde(default)]
-    provide_base: bool,
     context: Option<String>,
     build_args: Option<HashMap<String, String>>,
 }
@@ -57,7 +55,6 @@ impl FromStr for CrossTargetDockerfileConfig {
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         Ok(CrossTargetDockerfileConfig {
             file: s.to_string(),
-            provide_base: false,
             context: None,
             build_args: None,
         })
@@ -104,16 +101,6 @@ impl CrossToml {
         self.get_string(target, |t| t.dockerfile.as_ref().map(|c| &c.file))
     }
 
-    /// Returns the `target.{}.dockerfile.provide_base` part of `Cross.toml`
-    pub fn dockerfile_provide_base(&self, target: &Target) -> Option<bool> {
-        self.get_bool(
-            target,
-            |_| None,
-            |t| t.dockerfile.as_ref().map(|c| c.provide_base),
-        )
-        .1
-    }
-
     /// Returns the `target.{}.dockerfile.context` part of `Cross.toml`
     pub fn dockerfile_context(&self, target: &Target) -> Option<String> {
         self.get_string(target, |t| {

src/docker.rs

@@ -360,23 +360,15 @@ pub fn run(
         let context = config.dockerfile_context(target)?;
         let name = config.image(target)?;
 
-        let mut build = Dockerfile::File {
+        let build = Dockerfile::File {
             path: &path,
             context: context.as_deref(),
             name: name.as_deref(),
         };
 
-        if config.dockerfile_provide_base(target).unwrap_or_default() {
-            let mut content = format!("FROM {image}\n");
-            content.push_str(&crate::file::read(&path)?);
-            build = Dockerfile::Custom {
-                content,
-                from_file: true,
-            };
-        }
-
         image = build
             .build(
+                config,
                 &engine,
                 &host_root,
                 config.dockerfile_build_args(target)?.unwrap_or_default(),
@@ -397,10 +389,10 @@ ARG CROSS_DEB_ARCH=
 ARG CROSS_CMD
 RUN eval "${{CROSS_CMD}}""#
             ),
-            from_file: false,
         };
         custom
             .build(
+                config,
                 &engine,
                 &host_root,
                 Some(("CROSS_CMD", pre_build.join("\n"))),
@@ -428,14 +420,14 @@ pub enum Dockerfile<'a> {
     },
     Custom {
         content: String,
-        /// if `true`, the name of the file will be slightly different
-        from_file: bool,
     },
 }
 
 impl<'a> Dockerfile<'a> {
+    #[allow(clippy::too_many_arguments)]
     pub fn build(
         &self,
+        config: &Config,
         engine: &Path,
         host_root: &Path,
         build_args: impl IntoIterator<Item = (impl AsRef<str>, impl AsRef<str>)>,
@@ -454,20 +446,23 @@ impl<'a> Dockerfile<'a> {
         }
 
         if let Some(arch) = target_triple.deb_arch() {
-            docker_build.args(["--build-arg", &format!("CROSS_DEB_ARCH={}", arch)]);
+            docker_build.args(["--build-arg", &format!("CROSS_DEB_ARCH={arch}")]);
+        }
+
+        if let Ok(cross_base_image) = image(config, target_triple) {
+            docker_build.args([
+                "--build-arg",
+                &format!("CROSS_BASE_IMAGE={cross_base_image}"),
+            ]);
         }
 
         let path = match self {
             Dockerfile::File { path, .. } => PathBuf::from(path),
-            Dockerfile::Custom { content, from_file } => {
+            Dockerfile::Custom { content } => {
                 let path = host_root
                     .join("target")
                     .join(target_triple.to_string())
-                    .join(format!(
-                        "Dockerfile.{}{}",
-                        target_triple,
-                        if !from_file { "-custom" } else { "" }
-                    ));
+                    .join(format!("Dockerfile.{}", target_triple,));
                 {
                     let mut file = file::write_file(&path, true)?;
                     file.write_all(content.as_bytes())?;

src/lib.rs

@@ -238,9 +238,9 @@ impl Target {
     }
 
     /// Returns the architecture name according to `dpkg` naming convention
-    /// 
+    ///
     /// # Notes
-    /// 
+    ///
     /// Some of these make no sense to use in our standard images
     pub fn deb_arch(&self) -> Option<&'static str> {
         match self.triple() {