$(location ...) expansion and runtime data support for build scripts

- rustc_env now expands $(rootpath //package:target), for passing
the location of files that are needed at compile time
- build_script_env now expands $(execpath //package:target), for
passing the location of files or tools that are needed at build
script runtime
- cargo_script_build() now passes the data argument to the build
script runner, so the data is available at runtime

cargo/cargo_build_script.bzl

@@ -4,6 +4,19 @@ load("@io_bazel_rules_rust//rust:private/rustc.bzl", "BuildInfo", "DepInfo", "ge
 load("@io_bazel_rules_rust//rust:private/utils.bzl", "find_toolchain")
 load("@io_bazel_rules_rust//rust:rust.bzl", "rust_binary")
 
+def _expand_location(ctx, env, data):
+    if env.startswith("$(execpath ") or env.startswith("$(location "):
+        # build script runner will replace with execroot
+        return "${pwd}/" + ctx.expand_location(env, data)
+    else:
+        return env
+
+def _expand_locations(ctx):
+    "Expand $(execroot ...) references in user-provided env vars."
+    env = ctx.attr.build_script_env
+    data = getattr(ctx.attr, "data", [])
+    return dict([(k, _expand_location(ctx, v, data)) for (k, v) in env.items()])
+
 def _build_script_impl(ctx):
     """The implementation for the `_build_script_run` rule.
 
@@ -88,14 +101,14 @@ def _build_script_impl(ctx):
     for f in ctx.attr.crate_features:
         env["CARGO_FEATURE_" + f.upper().replace("-", "_")] = "1"
 
-    env.update(ctx.attr.build_script_env)
+    env.update(_expand_locations(ctx))
 
     tools = depset(
         direct = [
             script,
             ctx.executable._cargo_build_script_runner,
             toolchain.rustc,
-        ],
+        ] + ctx.files.data,
         transitive = toolchain_tools,
     )
 
@@ -164,6 +177,10 @@ _build_script_run = rule(
         "build_script_env": attr.string_dict(
             doc = "Environment variables for build scripts.",
         ),
+        "data": attr.label_list(
+            doc = "Data or tools required by the build script.",
+            allow_files = True,
+        ),
         "_cc_toolchain": attr.label(
             default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
         ),
@@ -188,6 +205,7 @@ def cargo_build_script(
         version = None,
         deps = [],
         build_script_env = {},
+        data = [],
         **kwargs):
     """Compile and execute a rust build script to generate build attributes
 
@@ -220,10 +238,16 @@ def cargo_build_script(
     cargo_build_script(
         name = "build_script",
         srcs = ["build.rs"],
-        # Data are shipped during execution.
-        data = ["src/lib.rs"],
-        # Environment variables passed during build.rs execution
-        build_script_env = {"CARGO_PKG_VERSION": "0.1.2"},
+        # Optional environment variables passed during build.rs compilation
+        rustc_env = {
+           "CARGO_PKG_VERSION": "0.1.2",
+        },
+        # Optional environment variables passed during build.rs execution
+        build_script_env = {
+            "SOME_TOOL_OR_FILE": "$(execroot @tool//:binary)"
+        }
+        # Optional data/tool dependencies
+        data = ["@tool//:binary"],
     )
 
     rust_library(
@@ -245,13 +269,15 @@ def cargo_build_script(
         version (str, optional): The semantic version (semver) of the crate.
         deps (list, optional): The dependencies of the crate defined by `crate_name`.
         build_script_env (dict, optional): Environment variables for build scripts.
+        data (list, optional): Files or tools needed by the build script.
         **kwargs: Forwards to the underlying `rust_binary` rule.
     """
     rust_binary(
         name = name + "_script_",
         crate_features = crate_features,
         version = version,
         deps = deps,
+        data = data,
         **kwargs
     )
     _build_script_run(
@@ -262,4 +288,5 @@ def cargo_build_script(
         version = version,
         build_script_env = build_script_env,
         deps = deps,
+        data = data,
     )

cargo/cargo_build_script_runner/bin.rs

@@ -48,7 +48,7 @@ fn main() -> Result<(), String> {
 
             let mut command = Command::new(exec_root.join(&progname));
             command
-                .current_dir(manifest_dir.clone())
+                .current_dir(&manifest_dir)
                 .envs(target_env_vars)
                 .env("OUT_DIR", out_dir_abs)
                 .env("CARGO_MANIFEST_DIR", manifest_dir)
@@ -92,6 +92,15 @@ fn main() -> Result<(), String> {
                 }
             }
 
+            // replace env vars with a ${pwd} prefix with the exec_root
+            for (key, value) in env::vars() {
+                let exec_root_str = exec_root.to_str().expect("exec_root not in utf8");
+                if value.starts_with("${pwd}") {
+                    env::set_var(key, value.replacen("${pwd}", exec_root_str, 1));
+                }
+            }
+
+
             let output = BuildScriptOutput::from_command(&mut command).map_err(|exit_code| {
                 format!(
                     "Build script process failed{}",

examples/env_locations/BUILD

@@ -0,0 +1,51 @@
+load(
+    "@io_bazel_rules_rust//rust:rust.bzl",
+    "rust_test",
+)
+load("@io_bazel_rules_rust//cargo:cargo_build_script.bzl", "cargo_build_script")
+
+# generate a file
+genrule(
+    name = "data_generator",
+    outs = ["generated.data"],
+    cmd = "echo hello > $@",
+)
+
+_data = [
+    # we should be able to read non-generated source/data files
+    "source.file",
+    # and generated files as well
+    "generated.data",
+    # we should also be able to access external binaries
+    # such as protoc.
+    "@com_google_protobuf//:protoc",
+]
+
+cargo_build_script(
+    name = "build",
+    srcs = ["build.rs"],
+    build_script_env = {
+        # both execpath and location should work
+        "SOURCE_FILE": "$(execpath source.file)",
+        "GENERATED_DATA": "$(location generated.data)",
+        "SOME_TOOL": "$(execpath @com_google_protobuf//:protoc)",
+    },
+    data = _data,
+)
+
+rust_test(
+    name = "test",
+    srcs = [
+        "main.rs",
+    ],
+    data = _data,
+    edition = "2018",
+    rustc_env = {
+        "SOURCE_FILE": "$(rootpath source.file)",
+        "GENERATED_DATA": "$(rootpath generated.data)",
+        "SOME_TOOL": "$(rootpath @com_google_protobuf//:protoc)",
+    },
+    deps = [
+        ":build",
+    ],
+)

examples/env_locations/build.rs

@@ -0,0 +1,17 @@
+use std::{fs,env};
+
+fn main() {
+    // our source file should be readable
+    let path = env::var("SOURCE_FILE").unwrap();
+    let generated_data = fs::read_to_string(&path).unwrap();
+    assert_eq!(generated_data, "source\n");
+
+    // our generated data file should be readable
+    let path = env::var("GENERATED_DATA").unwrap();
+    let generated_data = fs::read_to_string(&path).unwrap();
+    assert_eq!(generated_data, "hello\n");
+
+    // and we should be able to read (and thus execute) our tool
+    let path = env::var("SOME_TOOL").unwrap();
+    assert_eq!(fs::read(&path).unwrap().is_empty(), false);
+}

examples/env_locations/main.rs

@@ -0,0 +1,11 @@
+#[test]
+fn test() {
+    // our source file should be readable
+    let source_file = std::fs::read_to_string(env!("SOURCE_FILE")).unwrap();
+    assert_eq!(source_file, "source\n");
+    // our generated data file should be readable
+    let generated_data = std::fs::read_to_string(env!("GENERATED_DATA")).unwrap();
+    assert_eq!(generated_data, "hello\n");
+    // and we should be able to read (and thus execute) our tool
+    assert_eq!(std::fs::read(env!("SOME_TOOL")).unwrap().is_empty(), false);
+}

examples/env_locations/source.file

@@ -0,0 +1 @@
+source

rust/private/clippy.bzl

@@ -92,6 +92,7 @@ def _clippy_aspect_impl(target, ctx):
         build_env_file = build_env_file,
         build_flags_files = build_flags_files,
         maker_path = clippy_marker.path,
+        aspect = True,
     )
 
     # Deny the default-on clippy warning levels.

rust/private/rust.bzl

@@ -417,6 +417,12 @@ _rust_common_attrs = {
     "rustc_env": attr.string_dict(
         doc = _tidy("""
             Dictionary of additional `"key": "value"` environment variables to set for rustc.
+
+            rust_test()/rust_binary() rules can use $(rootpath //package:target) to pass in the
+            location of a generated file or external tool. Cargo build scripts that wish to
+            expand locations should use cargo_build_script()'s build_script_env argument instead,
+            as build scripts are run in a different environment - see cargo_build_script()'s
+            documentation for more.
         """),
     ),
     "crate_features": attr.string_list(

rust/private/rustc.bzl

@@ -311,6 +311,15 @@ def get_linker_and_args(ctx, cc_toolchain, feature_configuration, rpaths):
 
     return ld, link_args, link_env
 
+def _expand_locations(ctx, env, aspect):
+    "Expand $(rootpath ...) references in user-provided env vars."
+    if aspect:
+        data = getattr(ctx.rule.attr, "data", [])
+    else:
+        data = getattr(ctx.attr, "data", [])
+
+    return dict([(k, ctx.expand_location(v, data)) for (k, v) in env.items()])
+
 def _process_build_scripts(
         ctx,
         file,
@@ -400,7 +409,8 @@ def construct_arguments(
         out_dir,
         build_env_file,
         build_flags_files,
-        maker_path = None):
+        maker_path = None,
+        aspect = False):
     """Builds an Args object containing common rustc flags
 
     Args:
@@ -418,6 +428,7 @@ def construct_arguments(
         build_env_file (str): The output file of a `cargo_build_script` action containing rustc environment variables
         build_flags_files (list): The output files of a `cargo_build_script` actions containing rustc build flags
         maker_path (File): An optional clippy marker file
+        aspect (bool): True if called in an aspect context.
 
     Returns:
         tuple: A tuple of the following items
@@ -549,7 +560,7 @@ def construct_arguments(
                 env["CARGO_BIN_EXE_" + dep_crate_info.output.basename] = dep_crate_info.output.short_path
 
     # Update environment with user provided variables.
-    env.update(crate_info.rustc_env)
+    env.update(_expand_locations(ctx, crate_info.rustc_env, aspect))
 
     # This empty value satisfies Clippy, which otherwise complains about the
     # sysroot being undefined.