Read default annotation values from package's Cargo.toml metadata

crate_universe/src/config.rs

@@ -161,7 +161,7 @@ pub enum Checksumish {
     },
 }
 
-#[derive(Debug, Default, Deserialize, Serialize, Clone)]
+#[derive(Debug, Default, Deserialize, Serialize, Clone, PartialEq)]
 pub struct CrateAnnotations {
     /// Which subset of the crate's bins should get produced as `rust_binary` targets.
     pub gen_binaries: Option<GenBinaries>,
@@ -335,6 +335,89 @@ impl Sum for CrateAnnotations {
     }
 }
 
+/// A subset of `crate.annotation` that we allow packages to define in their
+/// free-form Cargo.toml metadata.
+///
+/// ```toml
+/// [package.metadata.bazel]
+/// additive_build_file_contents = """
+///     ...
+/// """
+/// data = ["font.woff2"]
+/// extra_aliased_targets = { ... }
+/// gen_build_script = false
+/// ```
+///
+/// These are considered default values which apply if the Bazel workspace does
+/// not specify a different value for the same annotation in their
+/// crates_repository attributes.
+#[derive(Debug, Deserialize)]
+pub struct AnnotationsProvidedByPackage {
+    pub gen_build_script: Option<bool>,
+    pub data: Option<BTreeSet<String>>,
+    pub data_glob: Option<BTreeSet<String>>,
+    pub compile_data: Option<BTreeSet<String>>,
+    pub compile_data_glob: Option<BTreeSet<String>>,
+    pub rustc_env: Option<BTreeMap<String, String>>,
+    pub rustc_env_files: Option<BTreeSet<String>>,
+    pub rustc_flags: Option<Vec<String>>,
+    pub build_script_env: Option<BTreeMap<String, String>>,
+    pub build_script_rustc_env: Option<BTreeMap<String, String>>,
+    pub additive_build_file_content: Option<String>,
+    pub extra_aliased_targets: Option<BTreeMap<String, String>>,
+}
+
+impl CrateAnnotations {
+    pub fn apply_defaults_from_package_metadata(&mut self, pkg_metadata: &serde_json::Value) {
+        #[deny(unused_variables)]
+        let AnnotationsProvidedByPackage {
+            gen_build_script,
+            data,
+            data_glob,
+            compile_data,
+            compile_data_glob,
+            rustc_env,
+            rustc_env_files,
+            rustc_flags,
+            build_script_env,
+            build_script_rustc_env,
+            additive_build_file_content,
+            extra_aliased_targets,
+        } = match AnnotationsProvidedByPackage::deserialize(&pkg_metadata["bazel"]) {
+            Ok(annotations) => annotations,
+            // Ignore bad annotations. The set of supported annotations evolves
+            // over time across different versions of crate_universe, and we
+            // don't want a library to be impossible to import into Bazel for
+            // having old or broken annotations. The Bazel workspace can specify
+            // its own correct annotations.
+            Err(_) => return,
+        };
+
+        fn default<T>(workspace_value: &mut Option<T>, default_value: Option<T>) {
+            if workspace_value.is_none() {
+                *workspace_value = default_value;
+            }
+        }
+
+        default(&mut self.gen_build_script, gen_build_script);
+        default(&mut self.gen_build_script, gen_build_script);
+        default(&mut self.data, data);
+        default(&mut self.data_glob, data_glob);
+        default(&mut self.compile_data, compile_data);
+        default(&mut self.compile_data_glob, compile_data_glob);
+        default(&mut self.rustc_env, rustc_env);
+        default(&mut self.rustc_env_files, rustc_env_files);
+        default(&mut self.rustc_flags, rustc_flags);
+        default(&mut self.build_script_env, build_script_env);
+        default(&mut self.build_script_rustc_env, build_script_rustc_env);
+        default(
+            &mut self.additive_build_file_content,
+            additive_build_file_content,
+        );
+        default(&mut self.extra_aliased_targets, extra_aliased_targets);
+    }
+}
+
 /// A unique identifier for Crates
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone)]
 pub struct CrateId {
@@ -444,7 +527,7 @@ impl std::fmt::Display for CrateId {
     }
 }
 
-#[derive(Debug, Hash, Clone)]
+#[derive(Debug, Hash, Clone, PartialEq)]
 pub enum GenBinaries {
     All,
     Some(BTreeSet<String>),

crate_universe/src/metadata/metadata_annotation.rs

@@ -383,7 +383,7 @@ impl Annotations {
             .packages
             .iter()
             .filter_map(|(pkg_id, pkg)| {
-                let extras: Vec<CrateAnnotations> = config
+                let mut crate_extra: CrateAnnotations = config
                     .annotations
                     .iter()
                     .filter(|(id, _)| id.matches(pkg))
@@ -395,18 +395,20 @@ impl Annotations {
                         extra
                     })
                     .cloned()
-                    .collect();
+                    .sum();
 
-                if !extras.is_empty() {
+                crate_extra.apply_defaults_from_package_metadata(&pkg.metadata);
+
+                if crate_extra == CrateAnnotations::default() {
+                    None
+                } else {
                     Some((
                         CrateId::new(pkg.name.clone(), pkg.version.to_string()),
                         PairredExtras {
                             package_id: pkg_id.clone(),
-                            crate_extra: extras.into_iter().sum(),
+                            crate_extra,
                         },
                     ))
-                } else {
-                    None
                 }
             })
             .collect();
@@ -560,4 +562,42 @@ mod test {
         assert!(result_str.contains("Unused annotations were provided. Please remove them"));
         assert!(result_str.contains("mock-crate"));
     }
+
+    #[test]
+    fn defaults_from_package_metadata() {
+        let crate_id = CrateId::new("has_package_metadata".to_owned(), "0.0.0".to_owned());
+        let annotations = CrateAnnotations {
+            rustc_env: Some({
+                let mut rustc_env = BTreeMap::new();
+                rustc_env.insert("BAR".to_owned(), "bar is set".to_owned());
+                rustc_env
+            }),
+            ..CrateAnnotations::default()
+        };
+
+        let mut config = Config::default();
+        config
+            .annotations
+            .insert(crate_id.clone(), annotations.clone());
+
+        // Combine the above annotations with default values provided by the
+        // crate author in package metadata.
+        let combined_annotations = Annotations::new(
+            test::metadata::has_package_metadata(),
+            test::lockfile::has_package_metadata(),
+            config,
+        )
+        .unwrap();
+
+        let extras = &combined_annotations.pairred_extras[&crate_id].crate_extra;
+        let expected = CrateAnnotations {
+            // This comes from has_package_metadata's [package.metadata.bazel].
+            additive_build_file_content: Some("genrule(**kwargs)\n".to_owned()),
+            // The package metadata defines a default rustc_env containing FOO,
+            // but it is superseded by a rustc_env annotation containing only
+            // BAR. These dictionaries are intentionally not merged together.
+            ..annotations
+        };
+        assert_eq!(*extras, expected);
+    }
 }

crate_universe/src/test.rs

@@ -114,6 +114,14 @@ pub mod metadata {
         )))
         .unwrap()
     }
+
+    pub fn has_package_metadata() -> cargo_metadata::Metadata {
+        serde_json::from_str(include_str!(concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/test_data/metadata/has_package_metadata/metadata.json"
+        )))
+        .unwrap()
+    }
 }
 
 pub mod lockfile {
@@ -174,4 +182,12 @@ pub mod lockfile {
         )))
         .unwrap()
     }
+
+    pub fn has_package_metadata() -> cargo_lock::Lockfile {
+        cargo_lock::Lockfile::from_str(include_str!(concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/test_data/metadata/has_package_metadata/Cargo.lock"
+        )))
+        .unwrap()
+    }
 }

crate_universe/test_data/metadata/has_package_metadata/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "has_package_metadata"
+version = "0.0.0"
+edition = "2021"
+
+# Required to satisfy cargo but no `lib.rs` is expected to
+# exist within test data.
+[lib]
+path = "lib.rs"
+
+[package.metadata.bazel]
+additive_build_file_content = """
+genrule(**kwargs)
+"""
+rustc_env = { "FOO" = "foo is set" }

examples/crate_universe/WORKSPACE.bazel

@@ -277,35 +277,14 @@ no_cargo_crate_repositories()
 
 crates_repository(
     name = "using_cxx",
-    annotations = {
-        # CXX provides a header file that should be used in C++ sources that depend on cxx.
-        "cxx": [
-            crate.annotation(
-                additive_build_file_content = """
-                # This file is included in the BUILD for the cxx crate, to export its header
-                # file for C++ code to depend on.
-                cc_library(
-                    name = "cxx_cc",
-                    visibility = ["//visibility:public"],
-                    hdrs = ["include/cxx.h"],
-                    srcs = ["src/cxx.cc"],
-                    includes = ["include"],
-                    linkstatic = True,
-                )
-            """,
-                extra_aliased_targets = {"cxx_cc": "cxx_cc"},
-                gen_build_script = False,
-            ),
-        ],
-    },
     cargo_lockfile = "//using_cxx:Cargo.Bazel.lock",
     # `generator` is not necessary in official releases.
     # See load satement for `cargo_bazel_bootstrap`.
     generator = "@cargo_bazel_bootstrap//:cargo-bazel",
     lockfile = "//using_cxx:cargo-bazel-lock.json",
     packages = {
         "cxx": crate.spec(
-            version = "1.0.0",
+            version = "1.0.105",
         ),
     },
     splicing_config = splicing_config(
@@ -341,10 +320,10 @@ rust_binary(
     ),
 )
     """,
-    sha256 = "df13eece12ed9e7bd4fb071a6af4c44421bb9024d339d029f5333bcdaca00000",
-    strip_prefix = "cxxbridge-cmd-1.0.100",
+    sha256 = "0b3eea393dbcbc1e875302846de4e4f9a31bf2e57ad3657bc83d61d00293b0fe",
+    strip_prefix = "cxxbridge-cmd-1.0.105",
     type = "tar.gz",
-    urls = ["https://crates.io/api/v1/crates/cxxbridge-cmd/1.0.100/download"],
+    urls = ["https://crates.io/api/v1/crates/cxxbridge-cmd/1.0.105/download"],
 )
 
 crates_repository(