Support sys-crates build script dependencies.

cargo/cargo_build_script.bzl

@@ -1,14 +1,24 @@
-load("@io_bazel_rules_rust//rust:private/rustc.bzl", "BuildInfo", "get_compilation_mode_opts")
+load("@io_bazel_rules_rust//rust:private/rustc.bzl", "BuildInfo", "DepInfo", "get_compilation_mode_opts")
 load("@io_bazel_rules_rust//rust:private/utils.bzl", "find_toolchain")
 load("@io_bazel_rules_rust//rust:rust.bzl", "rust_binary")
 
 def _cargo_build_script_run(ctx, script):
     toolchain = find_toolchain(ctx)
     out_dir = ctx.actions.declare_directory(ctx.label.name + ".out_dir")
     env_out = ctx.actions.declare_file(ctx.label.name + ".env")
+    dep_env_out = ctx.actions.declare_file(ctx.label.name + ".depenv")
     flags_out = ctx.actions.declare_file(ctx.label.name + ".flags")
     manifest_dir = "%s.runfiles/%s" % (script.path, ctx.label.workspace_name or ctx.workspace_name)
     compilation_mode_opt_level = get_compilation_mode_opts(ctx, toolchain).opt_level
+
+    crate_name = ctx.attr.crate_name
+    # Derive crate name from the rule label which is <crate_name>_build_script if not provided.
+    if not crate_name:
+        crate_name = ctx.label.name
+        if crate_name.endswith("_build_script"):
+            crate_name = crate_name.replace("_build_script", "")
+        crate_name = crate_name.replace("_", "-")
+
     env = {
         "CARGO_CFG_TARGET_ARCH": toolchain.target_arch,
         "CARGO_MANIFEST_DIR": manifest_dir,
@@ -36,11 +46,26 @@ def _cargo_build_script_run(ctx, script):
         ],
     )
 
-    ctx.actions.run(
-        executable = ctx.executable._cargo_build_script_runner,
-        arguments = [script.path, env_out.path, flags_out.path],
-        outputs = [out_dir, env_out, flags_out],
+    # dep_env_file contains additional environment variables coming from
+    # direct dependency sys-crates' build scripts. These need to be made
+    # available to the current crate build script.
+    # See https://doc.rust-lang.org/cargo/reference/build-scripts.html#-sys-packages
+    # for details.
+    cmd = ""
+    dep_env_files = []
+    for dep in ctx.attr.deps:
+        if DepInfo in dep and dep[DepInfo].dep_env:
+            dep_env_file = dep[DepInfo].dep_env
+            cmd += "export $(cat %s); " % dep_env_file.path
+            dep_env_files.append(dep_env_file)
+    cmd += "$@"
+
+    ctx.actions.run_shell(
+        command = cmd,
+        arguments = [ctx.executable._cargo_build_script_runner.path, script.path, crate_name, env_out.path, flags_out.path, dep_env_out.path],
+        outputs = [out_dir, env_out, flags_out, dep_env_out],
         tools = tools,
+        inputs = dep_env_files,
         mnemonic = "CargoBuildScriptRun",
         env = env,
     )
@@ -49,6 +74,7 @@ def _cargo_build_script_run(ctx, script):
         BuildInfo(
             out_dir = out_dir,
             rustc_env = env_out,
+            dep_env = dep_env_out,
             flags = flags_out,
         ),
     ]
@@ -66,20 +92,22 @@ _build_script_run = rule(
             cfg = "host",
             doc = "The binary script to run, generally a rust_binary target. ",
         ),
+        "crate_name": attr.string(),
         "crate_features": attr.string_list(doc = "The list of rust features that the build script should consider activated."),
         "_cargo_build_script_runner": attr.label(
             executable = True,
             allow_files = True,
             default = Label("//cargo/cargo_build_script_runner:cargo_build_script_runner"),
             cfg = "host",
         ),
+        "deps": attr.label_list(),
     },
     toolchains = [
         "@io_bazel_rules_rust//rust:toolchain",
     ],
 )
 
-def cargo_build_script(name, crate_features=[], **kwargs):
+def cargo_build_script(name, crate_name="", crate_features=[], deps=[], **kwargs):
     """
     Compile and execute a rust build script to generate build attributes
 
@@ -128,12 +156,16 @@ def cargo_build_script(name, crate_features=[], **kwargs):
     The `hello_lib` target will be build with the flags and the environment variables declared by the
     build script in addition to the file generated by it.
     """
-    rust_binary(name = name + "_script_",
+    rust_binary(
+        name = name + "_script_",
         crate_features = crate_features,
+        deps = deps,
         **kwargs,
     )
     _build_script_run(
         name = name,
         script = ":%s_script_" % name,
+        crate_name = crate_name,
         crate_features = crate_features,
+        deps = deps,
     )

cargo/cargo_build_script_runner/bin.rs

@@ -33,8 +33,8 @@ fn main() {
     let manifest_dir = canonicalize(&manifest_dir_env).expect(&format!("Failed to canonicalize '{}'", manifest_dir_env));
     let out_dir = canonicalize(&out_dir_env).expect(&format!("Failed to canonicalize '{}'", out_dir_env));
     let rustc = canonicalize(&rustc_env).expect(&format!("Failed to canonicalize '{}'", rustc_env));
-    match (args.next(), args.next(), args.next()) {
-        (Some(progname), Some(envfile), Some(flagfile)) => {
+    match (args.next(), args.next(), args.next(), args.next(), args.next()) {
+        (Some(progname), Some(crate_name), Some(envfile), Some(flagfile), Some(depenvfile)) => {
             let output = BuildScriptOutput::from_command(
                     Command::new(
                         canonicalize(&progname).expect(&format!("Failed to canonicalize '{}'", progname)))
@@ -47,13 +47,17 @@ fn main() {
                 File::create(&envfile).expect(&format!("Unable to create file {}", envfile));
             f.write_all(BuildScriptOutput::to_env(&output).as_bytes())
                 .expect(&format!("Unable to write file {}", envfile));
+            let mut f =
+                File::create(&depenvfile).expect(&format!("Unable to create file {}", depenvfile));
+            f.write_all(BuildScriptOutput::to_dep_env(&output, &crate_name).as_bytes())
+                .expect(&format!("Unable to write file {}", depenvfile));
             let mut f =
                 File::create(&flagfile).expect(&format!("Unable to create file {}", flagfile));
             f.write_all(BuildScriptOutput::to_flags(&output).as_bytes())
                 .expect(&format!("Unable to write file {}", flagfile));
         }
         _ => {
-            eprintln!("Usage: $0 progname envfile flagfile [arg1...argn]");
+            eprintln!("Usage: $0 progname crate_name envfile flagfile depenvfile [arg1...argn]");
             exit(1);
         }
     }

cargo/cargo_build_script_runner/lib.rs

@@ -30,6 +30,8 @@ pub enum BuildScriptOutput {
     Flags(String),
     /// cargo:rustc-env
     Env(String),
+    /// cargo:VAR=VALUE
+    DepEnv(String),
 }
 
 impl BuildScriptOutput {
@@ -45,26 +47,33 @@ impl BuildScriptOutput {
             return None;
         }
         let param = split[1].trim().to_owned();
-        match split[0] {
-            "cargo:rustc-link-lib" => Some(BuildScriptOutput::LinkLib(param)),
-            "cargo:rustc-link-search" => Some(BuildScriptOutput::LinkSearch(param)),
-            "cargo:rustc-cfg" => Some(BuildScriptOutput::Cfg(param)),
-            "cargo:rustc-flags" => Some(BuildScriptOutput::Flags(param)),
-            "cargo:rustc-env" => Some(BuildScriptOutput::Env(param)),
-            "cargo:rerun-if-changed" | "cargo:rerun-if-env-changed" =>
+        let key_split = split[0].splitn(2, ':').collect::<Vec<_>>();
+        if key_split.len() <= 1 || key_split[0] != "cargo" {
+            // Not a cargo directive.
+            return None
+        }
+        match key_split[1] {
+            "rustc-link-lib" => Some(BuildScriptOutput::LinkLib(param)),
+            "rustc-link-search" => Some(BuildScriptOutput::LinkSearch(param)),
+            "rustc-cfg" => Some(BuildScriptOutput::Cfg(param)),
+            "rustc-flags" => Some(BuildScriptOutput::Flags(param)),
+            "rustc-env" => Some(BuildScriptOutput::Env(param)),
+            "rerun-if-changed" | "rerun-if-env-changed" =>
                 // Ignored because Bazel will re-run if those change all the time.
                 None,
-            "cargo:warning" => {
+            "warning" => {
                 eprintln!("Build Script Warning: {}", split[1]);
                 None
             },
-            _ => {
-                // Not yet supported:
-                // cargo:KEY=VALUE — Metadata, used by links scripts.
+            "rustc-cdylib-link-arg" => {
                 // cargo:rustc-cdylib-link-arg=FLAG — Passes custom flags to a linker for cdylib crates.
                 eprintln!("Warning: build script returned unsupported directive `{}`", split[0]);
                 None
             },
+            _ => {
+                // cargo:KEY=VALUE — Metadata, used by links scripts.
+                Some(BuildScriptOutput::DepEnv(format!("{}={}", key_split[1].to_uppercase(), param)))
+            },
         }
     }
 
@@ -109,6 +118,28 @@ impl BuildScriptOutput {
             .join(" ")
     }
 
+    /// Convert a vector of [BuildScriptOutput] into a list of dependencies environment variables.
+    pub fn to_dep_env(v: &Vec<BuildScriptOutput>, crate_name: &str) -> String {
+        // TODO: make use of `strip_suffix`.
+        const SYS_CRATE_SUFFIX: &str = "-sys";
+        let name = if crate_name.ends_with(SYS_CRATE_SUFFIX) {
+            crate_name.split_at(crate_name.rfind(SYS_CRATE_SUFFIX).unwrap()).0
+        } else {
+            crate_name
+        };
+        let prefix = format!("DEP_{}_", name.replace("-", "_").to_uppercase());
+        v.iter()
+            .filter_map(|x| {
+                if let BuildScriptOutput::DepEnv(env) = x {
+                    Some(format!("{}{}", prefix, env.to_owned()))
+                } else {
+                    None
+                }
+            })
+            .collect::<Vec<_>>()
+            .join(" ")
+    }
+
     /// Convert a vector of [BuildScriptOutput] into a flagfile.
     pub fn to_flags(v: &Vec<BuildScriptOutput>) -> String {
         v.iter()
@@ -138,14 +169,15 @@ cargo:rustc-env=FOO=BAR
 cargo:rustc-link-search=bleh
 cargo:rustc-env=BAR=FOO
 cargo:rustc-flags=-Lblah
-cargo:invalid=ignored
 cargo:rerun-if-changed=ignored
 cargo:rustc-cfg=feature=awesome
+cargo:version=123
+cargo:version_number=1010107f
 ",
         );
         let reader = BufReader::new(buff);
         let result = BuildScriptOutput::from_reader(reader);
-        assert_eq!(result.len(), 6);
+        assert_eq!(result.len(), 8);
         assert_eq!(result[0], BuildScriptOutput::LinkLib("sdfsdf".to_owned()));
         assert_eq!(result[1], BuildScriptOutput::Env("FOO=BAR".to_owned()));
         assert_eq!(result[2], BuildScriptOutput::LinkSearch("bleh".to_owned()));
@@ -155,7 +187,13 @@ cargo:rustc-cfg=feature=awesome
             result[5],
             BuildScriptOutput::Cfg("feature=awesome".to_owned())
         );
+        assert_eq!(result[6], BuildScriptOutput::DepEnv("VERSION=123".to_owned()));
+        assert_eq!(result[7], BuildScriptOutput::DepEnv("VERSION_NUMBER=1010107f".to_owned()));
 
+        assert_eq!(
+            BuildScriptOutput::to_dep_env(&result, "my-crate-sys"),
+            "DEP_MY_CRATE_VERSION=123 DEP_MY_CRATE_VERSION_NUMBER=1010107f".to_owned()
+        );
         assert_eq!(
             BuildScriptOutput::to_env(&result),
             "FOO=BAR BAR=FOO".to_owned()

rust/private/rustc.bzl

@@ -45,6 +45,7 @@ BuildInfo = provider(
         "flags": """File: file containing additional flags to pass to rustc""",
         "out_dir": """File: directory containing the result of a build script""",
         "rustc_env": """File: file containing additional environment variables to set for rustc.""",
+        "dep_env": """File: extra build script environment varibles to be set to direct dependencies.""",
     },
 )
 
@@ -62,6 +63,7 @@ DepInfo = provider(
         "transitive_dylibs": "depset[File]",
         "transitive_staticlibs": "depset[File]",
         "transitive_libs": "List[File]: All transitive dependencies, not filtered by type.",
+        "dep_env": """File: File with environment variables direct dependencies build scripts rely upon.""",
     },
 )
 
@@ -185,6 +187,7 @@ def collect_deps(label, deps, proc_macro_deps, aliases, toolchain):
             transitive_dylibs = transitive_dylibs,
             transitive_staticlibs = transitive_staticlibs,
             transitive_libs = transitive_libs.to_list(),
+            dep_env = build_info.dep_env if build_info else None,
         ),
         build_info,
     )