Add support for additional-targets in docs.rs config

Author: GuillaumeGomez

crates/metadata/lib.rs

@@ -1,4 +1,5 @@
 #![warn(missing_docs)]
+
 //! Collect information that allows you to build a crate the same way that docs.rs would.
 //!
 //! This library is intended for use in docs.rs and crater, but might be helpful to others.
@@ -138,6 +139,10 @@ pub struct Metadata {
     /// These cannot be a subcommand, they may only be options.
     #[serde(default)]
     cargo_args: Vec<String>,
+
+    /// List of additional targets to be generated. See [`BuildTargets`].
+    #[serde(default)]
+    additional_targets: Vec<String>,
 }
 
 /// The targets that should be built for a crate.
@@ -220,13 +225,22 @@ impl Metadata {
             })
             .unwrap_or(HOST_TARGET);
 
-        let crate_targets = self
-            .targets
-            .as_ref()
-            .map(|targets| targets.iter().map(String::as_str).collect());
+        let crate_targets = self.targets.as_ref().map(|targets| {
+            targets
+                .iter()
+                .chain(self.additional_targets.iter())
+                .map(String::as_str)
+                .collect()
+        });
         // Let people opt-in to only having specific targets
         let mut targets: HashSet<_> = if include_default_targets {
-            crate_targets.unwrap_or_else(|| DEFAULT_TARGETS.iter().copied().collect())
+            crate_targets.unwrap_or_else(|| {
+                DEFAULT_TARGETS
+                    .iter()
+                    .copied()
+                    .chain(self.additional_targets.iter().map(String::as_str))
+                    .collect()
+            })
         } else {
             crate_targets.unwrap_or_default()
         };
@@ -525,8 +539,6 @@ mod test_targets {
 
     #[test]
     fn test_select_targets() {
-        use super::BuildTargets;
-
         let mut metadata = Metadata::default();
 
         // unchanged default_target, targets not specified
@@ -637,6 +649,42 @@ mod test_targets {
         assert_eq!(others, tier_one_targets_no_default);
     }
 
+    #[test]
+    fn test_additional_targets() {
+        let mut metadata = Metadata {
+            targets: Some(
+                DEFAULT_TARGETS
+                    .iter()
+                    .map(|s| s.to_string())
+                    .collect::<Vec<_>>(),
+            ),
+            ..Default::default()
+        };
+
+        let additional_target = "i686-apple-darwin";
+        metadata.additional_targets = vec![additional_target.to_string()];
+        let BuildTargets {
+            other_targets: others,
+            ..
+        } = metadata.targets(true);
+
+        assert!(others.contains(additional_target), "no additional target");
+        for target in DEFAULT_TARGETS.iter().skip(1) {
+            assert!(others.contains(target), "missing {target}");
+        }
+
+        // Now we check that `additional_targets` also works if `targets` is set.
+        let target = "i686-pc-windows-msvc";
+        metadata.targets = Some(vec![target.to_string()]);
+        let BuildTargets {
+            other_targets: others,
+            default_target: default,
+        } = metadata.targets(true);
+        assert_eq!(others.len(), 1);
+        assert!(others.contains(additional_target));
+        assert_eq!(default, target);
+    }
+
     #[test]
     fn no_default_targets() {
         // if `targets` is unset, `other_targets` should be empty

templates/core/Cargo.toml.example

@@ -36,6 +36,9 @@ default-target = "x86_64-unknown-linux-gnu"
 #   all tier-one targets will be built and `x86_64-unknown-linux-gnu` will be used as the default target.
 targets = ["aarch64-apple-darwin", "x86_64-pc-windows-msvc"]
 
+# If you want to instead add another target without overwriting the default ones:
+additional-targets = ["i686-apple-darwin"]
+
 # Additional `RUSTFLAGS` to set (default: [])
 rustc-args = ["--example-rustc-arg"]