propagate buildscript link search paths to parent crate (#1123)

Adds a new `link_search_paths: File` field to `BuildInfo` provider.

Resolves #859

I use native Windows bindings through [windows-rs](https://github.com/microsoft/windows-rs) crate and it fails to link without propagating the link search path to a platform-dependent native library. The bindings call for a native library via `#[link(name = "windows")]` and propagate search path by a buildscript from a dependency (i.e. a transitive dependency for a root crate).

Propagating link search paths seems to be what is cargo doing.

cargo/cargo_build_script.bzl

@@ -45,6 +45,7 @@ def _build_script_impl(ctx):
     dep_env_out = ctx.actions.declare_file(ctx.label.name + ".depenv")
     flags_out = ctx.actions.declare_file(ctx.label.name + ".flags")
     link_flags = ctx.actions.declare_file(ctx.label.name + ".linkflags")
+    link_search_paths = ctx.actions.declare_file(ctx.label.name + ".linksearchpaths")  # rustc-link-search, propagated from transitive dependencies
     manifest_dir = "%s.runfiles/%s/%s" % (script.path, ctx.label.workspace_name or ctx.workspace_name, ctx.label.package)
     compilation_mode_opt_level = get_compilation_mode_opts(ctx, toolchain).opt_level
 
@@ -155,6 +156,7 @@ def _build_script_impl(ctx):
         env_out.path,
         flags_out.path,
         link_flags.path,
+        link_search_paths.path,
         dep_env_out.path,
         streams.stdout.path,
         streams.stderr.path,
@@ -171,7 +173,7 @@ def _build_script_impl(ctx):
     ctx.actions.run(
         executable = ctx.executable._cargo_build_script_runner,
         arguments = [args],
-        outputs = [out_dir, env_out, flags_out, link_flags, dep_env_out, streams.stdout, streams.stderr],
+        outputs = [out_dir, env_out, flags_out, link_flags, link_search_paths, dep_env_out, streams.stdout, streams.stderr],
         tools = tools,
         inputs = build_script_inputs,
         mnemonic = "CargoBuildScriptRun",
@@ -186,6 +188,7 @@ def _build_script_impl(ctx):
             dep_env = dep_env_out,
             flags = flags_out,
             link_flags = link_flags,
+            link_search_paths = link_search_paths,
         ),
         OutputGroupInfo(streams = depset([streams.stdout, streams.stderr])),
     ]

cargo/cargo_build_script_runner/bin.rs

@@ -41,6 +41,7 @@ fn run_buildrs() -> Result<(), String> {
         env_file,
         compile_flags_file,
         link_flags_file,
+        link_search_paths_file,
         output_dep_env_path,
         stdout_path,
         stderr_path,
@@ -162,12 +163,15 @@ fn run_buildrs() -> Result<(), String> {
     let CompileAndLinkFlags {
         compile_flags,
         link_flags,
+        link_search_paths,
     } = BuildScriptOutput::outputs_to_flags(&buildrs_outputs, &exec_root.to_string_lossy());
 
     write(&compile_flags_file, compile_flags.as_bytes())
         .unwrap_or_else(|_| panic!("Unable to write file {:?}", compile_flags_file));
     write(&link_flags_file, link_flags.as_bytes())
         .unwrap_or_else(|_| panic!("Unable to write file {:?}", link_flags_file));
+    write(&link_search_paths_file, link_search_paths.as_bytes())
+        .unwrap_or_else(|_| panic!("Unable to write file {:?}", link_search_paths_file));
     Ok(())
 }
 
@@ -179,6 +183,7 @@ struct Options {
     env_file: String,
     compile_flags_file: String,
     link_flags_file: String,
+    link_search_paths_file: String,
     output_dep_env_path: String,
     stdout_path: String,
     stderr_path: String,
@@ -190,14 +195,15 @@ fn parse_args() -> Result<Options, String> {
     let mut args = env::args().skip(1);
 
     // TODO: we should consider an alternative to positional arguments.
-    match (args.next(), args.next(), args.next(), args.next(), args.next(), args.next(), args.next(), args.next(), args.next()) {
+    match (args.next(), args.next(), args.next(), args.next(), args.next(), args.next(), args.next(), args.next(), args.next(), args.next()) {
         (
             Some(progname),
             Some(crate_links),
             Some(out_dir),
             Some(env_file),
             Some(compile_flags_file),
             Some(link_flags_file),
+            Some(link_search_paths_file),
             Some(output_dep_env_path),
             Some(stdout_path),
             Some(stderr_path),
@@ -209,14 +215,15 @@ fn parse_args() -> Result<Options, String> {
                 env_file,
                 compile_flags_file,
                 link_flags_file,
+                link_search_paths_file,
                 output_dep_env_path,
                 stdout_path,
                 stderr_path,
                 input_dep_env_paths: args.collect(),
             })
         }
         _ => {
-            Err(format!("Usage: $0 progname crate_links out_dir env_file compile_flags_file link_flags_file output_dep_env_path stdout_path stderr_path input_dep_env_paths[arg1...argn]\nArguments passed: {:?}", args.collect::<Vec<String>>()))
+            Err(format!("Usage: $0 progname crate_links out_dir env_file compile_flags_file link_flags_file link_search_paths_file output_dep_env_path stdout_path stderr_path input_dep_env_paths[arg1...argn]\nArguments passed: {:?}", args.collect::<Vec<String>>()))
         }
     }
 }

cargo/cargo_build_script_runner/lib.rs

@@ -21,6 +21,7 @@ use std::process::{Command, Output};
 pub struct CompileAndLinkFlags {
     pub compile_flags: String,
     pub link_flags: String,
+    pub link_search_paths: String,
 }
 
 /// Enum containing all the considered return value from the script
@@ -171,20 +172,23 @@ impl BuildScriptOutput {
     pub fn outputs_to_flags(outputs: &[BuildScriptOutput], exec_root: &str) -> CompileAndLinkFlags {
         let mut compile_flags = Vec::new();
         let mut link_flags = Vec::new();
+        let mut link_search_paths = Vec::new();
 
         for flag in outputs {
             match flag {
                 BuildScriptOutput::Cfg(e) => compile_flags.push(format!("--cfg={}", e)),
                 BuildScriptOutput::Flags(e) => compile_flags.push(e.to_owned()),
                 BuildScriptOutput::LinkArg(e) => compile_flags.push(format!("-Clink-arg={}", e)),
                 BuildScriptOutput::LinkLib(e) => link_flags.push(format!("-l{}", e)),
-                BuildScriptOutput::LinkSearch(e) => link_flags.push(format!("-L{}", e)),
+                BuildScriptOutput::LinkSearch(e) => link_search_paths.push(format!("-L{}", e)),
                 _ => {}
             }
         }
+
         CompileAndLinkFlags {
             compile_flags: compile_flags.join("\n"),
             link_flags: Self::redact_exec_root(&link_flags.join("\n"), exec_root),
+            link_search_paths: Self::redact_exec_root(&link_search_paths.join("\n"), exec_root),
         }
     }
 
@@ -279,7 +283,8 @@ cargo:rustc-link-arg=Metal
                 compile_flags:
                     "-Lblah\n--cfg=feature=awesome\n-Clink-arg=-weak_framework\n-Clink-arg=Metal"
                         .to_owned(),
-                link_flags: "-lsdfsdf\n-L${pwd}/bleh".to_owned(),
+                link_flags: "-lsdfsdf".to_owned(),
+                link_search_paths: "-L${pwd}/bleh".to_owned(),
             }
         );
     }

docs/flatten.md

@@ -1386,8 +1386,8 @@ A provider containing general Crate information.
 ## DepInfo
 
 <pre>
-DepInfo(<a href="#DepInfo-dep_env">dep_env</a>, <a href="#DepInfo-direct_crates">direct_crates</a>, <a href="#DepInfo-transitive_build_infos">transitive_build_infos</a>, <a href="#DepInfo-transitive_crate_outputs">transitive_crate_outputs</a>, <a href="#DepInfo-transitive_crates">transitive_crates</a>,
-        <a href="#DepInfo-transitive_noncrates">transitive_noncrates</a>)
+DepInfo(<a href="#DepInfo-dep_env">dep_env</a>, <a href="#DepInfo-direct_crates">direct_crates</a>, <a href="#DepInfo-link_search_path_files">link_search_path_files</a>, <a href="#DepInfo-transitive_build_infos">transitive_build_infos</a>,
+        <a href="#DepInfo-transitive_crate_outputs">transitive_crate_outputs</a>, <a href="#DepInfo-transitive_crates">transitive_crates</a>, <a href="#DepInfo-transitive_noncrates">transitive_noncrates</a>)
 </pre>
 
 A provider containing information about a Crate's dependencies.
@@ -1399,6 +1399,7 @@ A provider containing information about a Crate's dependencies.
 | :------------- | :------------- |
 | <a id="DepInfo-dep_env"></a>dep_env |  File: File with environment variables direct dependencies build scripts rely upon.    |
 | <a id="DepInfo-direct_crates"></a>direct_crates |  depset[AliasableDepInfo]    |
+| <a id="DepInfo-link_search_path_files"></a>link_search_path_files |  depset[File]: All transitive files containing search paths to pass to the linker    |
 | <a id="DepInfo-transitive_build_infos"></a>transitive_build_infos |  depset[BuildInfo]    |
 | <a id="DepInfo-transitive_crate_outputs"></a>transitive_crate_outputs |  depset[File]: All transitive crate outputs.    |
 | <a id="DepInfo-transitive_crates"></a>transitive_crates |  depset[CrateInfo]    |

docs/providers.md

@@ -42,8 +42,8 @@ A provider containing general Crate information.
 ## DepInfo
 
 <pre>
-DepInfo(<a href="#DepInfo-dep_env">dep_env</a>, <a href="#DepInfo-direct_crates">direct_crates</a>, <a href="#DepInfo-transitive_build_infos">transitive_build_infos</a>, <a href="#DepInfo-transitive_crate_outputs">transitive_crate_outputs</a>, <a href="#DepInfo-transitive_crates">transitive_crates</a>,
-        <a href="#DepInfo-transitive_noncrates">transitive_noncrates</a>)
+DepInfo(<a href="#DepInfo-dep_env">dep_env</a>, <a href="#DepInfo-direct_crates">direct_crates</a>, <a href="#DepInfo-link_search_path_files">link_search_path_files</a>, <a href="#DepInfo-transitive_build_infos">transitive_build_infos</a>,
+        <a href="#DepInfo-transitive_crate_outputs">transitive_crate_outputs</a>, <a href="#DepInfo-transitive_crates">transitive_crates</a>, <a href="#DepInfo-transitive_noncrates">transitive_noncrates</a>)
 </pre>
 
 A provider containing information about a Crate's dependencies.
@@ -55,6 +55,7 @@ A provider containing information about a Crate's dependencies.
 | :------------- | :------------- |
 | <a id="DepInfo-dep_env"></a>dep_env |  File: File with environment variables direct dependencies build scripts rely upon.    |
 | <a id="DepInfo-direct_crates"></a>direct_crates |  depset[AliasableDepInfo]    |
+| <a id="DepInfo-link_search_path_files"></a>link_search_path_files |  depset[File]: All transitive files containing search paths to pass to the linker    |
 | <a id="DepInfo-transitive_build_infos"></a>transitive_build_infos |  depset[BuildInfo]    |
 | <a id="DepInfo-transitive_crate_outputs"></a>transitive_crate_outputs |  depset[File]: All transitive crate outputs.    |
 | <a id="DepInfo-transitive_crates"></a>transitive_crates |  depset[CrateInfo]    |

rust/private/providers.bzl

@@ -45,6 +45,7 @@ DepInfo = provider(
     fields = {
         "dep_env": "File: File with environment variables direct dependencies build scripts rely upon.",
         "direct_crates": "depset[AliasableDepInfo]",
+        "link_search_path_files": "depset[File]: All transitive files containing search paths to pass to the linker",
         "transitive_build_infos": "depset[BuildInfo]",
         "transitive_crate_outputs": "depset[File]: All transitive crate outputs.",
         "transitive_crates": "depset[CrateInfo]",
@@ -58,6 +59,7 @@ BuildInfo = provider(
         "dep_env": "File: extra build script environment varibles to be set to direct dependencies.",
         "flags": "File: file containing additional flags to pass to rustc",
         "link_flags": "File: file containing flags to pass to the linker",
+        "link_search_paths": "File: file containing search paths to pass to the linker",
         "out_dir": "File: directory containing the result of a build script",
         "rustc_env": "File: file containing additional environment variables to set for rustc.",
     },

rust/private/rustc.bzl

@@ -141,6 +141,7 @@ def collect_deps(
     transitive_crates = []
     transitive_noncrates = []
     transitive_build_infos = []
+    transitive_link_search_paths = []
     build_info = None
     linkstamps = []
     transitive_crate_outputs = []
@@ -175,6 +176,8 @@ def collect_deps(
             )
             transitive_noncrates.append(dep_info.transitive_noncrates)
             transitive_build_infos.append(dep_info.transitive_build_infos)
+            transitive_link_search_paths.append(dep_info.link_search_path_files)
+
         elif cc_info:
             # This dependency is a cc_library
             transitive_noncrates.append(cc_info.linking_context.linker_inputs)
@@ -184,6 +187,7 @@ def collect_deps(
                      "only one is allowed in the dependencies")
             build_info = dep_build_info
             transitive_build_infos.append(depset([build_info]))
+            transitive_link_search_paths.append(depset([build_info.link_search_paths]))
         else:
             fail("rust targets can only depend on rust_library, rust_*_library or cc_library " +
                  "targets.")
@@ -200,6 +204,7 @@ def collect_deps(
             ),
             transitive_crate_outputs = depset(transitive = transitive_crate_outputs),
             transitive_build_infos = depset(transitive = transitive_build_infos),
+            link_search_path_files = depset(transitive = transitive_link_search_paths),
             dep_env = build_info.dep_env if build_info else None,
         ),
         build_info,
@@ -298,23 +303,24 @@ def get_linker_and_args(ctx, attr, cc_toolchain, feature_configuration, rpaths):
 
 def _process_build_scripts(
         build_info,
+        dep_info,
         compile_inputs):
     """Gathers the outputs from a target's `cargo_build_script` action.
 
     Args:
         build_info (BuildInfo): The target Build's dependency info.
+        dep_info (DepInfo): The Depinfo provider form the target Crate's set of inputs.
         compile_inputs (depset): A set of all files that will participate in the build.
 
     Returns:
         tuple: A tuple: A tuple of the following items:
-            - (list): A list of all build info `OUT_DIR` File objects
+            - (depset[File]): A list of all build info `OUT_DIR` File objects
             - (str): The `OUT_DIR` of the current build info
             - (File): An optional path to a generated environment file from a `cargo_build_script` target
-            - (list): All direct and transitive build flags from the current build info.
+            - (depset[File]): All direct and transitive build flags from the current build info.
     """
-    extra_inputs, out_dir, build_env_file, build_flags_files = _create_extra_input_args(build_info)
-    if extra_inputs:
-        compile_inputs = depset(extra_inputs, transitive = [compile_inputs])
+    extra_inputs, out_dir, build_env_file, build_flags_files = _create_extra_input_args(build_info, dep_info)
+    compile_inputs = depset(transitive = [extra_inputs, compile_inputs])
     return compile_inputs, out_dir, build_env_file, build_flags_files
 
 def collect_inputs(
@@ -350,7 +356,7 @@ def collect_inputs(
             - (list): A list of all build info `OUT_DIR` File objects
             - (str): The `OUT_DIR` of the current build info
             - (File): An optional path to a generated environment file from a `cargo_build_script` target
-            - (list): All direct and transitive build flags from the current build info
+            - (depset[File]): All direct and transitive build flag files from the current build info
             - (list[File]): Linkstamp outputs.
     """
     linker_script = getattr(file, "linker_script") if hasattr(file, "linker_script") else None
@@ -432,7 +438,7 @@ def collect_inputs(
     )
 
     build_env_files = getattr(files, "rustc_env_files", [])
-    compile_inputs, out_dir, build_env_file, build_flags_files = _process_build_scripts(build_info, compile_inputs)
+    compile_inputs, out_dir, build_env_file, build_flags_files = _process_build_scripts(build_info, dep_info, compile_inputs)
     if build_env_file:
         build_env_files = [f for f in build_env_files] + [build_env_file]
     compile_inputs = depset(build_env_files, transitive = [compile_inputs])
@@ -477,7 +483,7 @@ def construct_arguments(
         rust_flags (list): Additional flags to pass to rustc
         out_dir (str): The path to the output directory for the target Crate.
         build_env_files (list): Files containing rustc environment variables, for instance from `cargo_build_script` actions.
-        build_flags_files (list): The output files of a `cargo_build_script` actions containing rustc build flags
+        build_flags_files (depset): The output files of a `cargo_build_script` actions containing rustc build flags
         emit (list): Values for the --emit flag to rustc.
         force_all_deps_direct (bool, optional): Whether to pass the transitive rlibs with --extern
             to the commandline as opposed to -L.
@@ -925,18 +931,19 @@ def add_edition_flags(args, crate):
     if crate.edition != "2015":
         args.add("--edition={}".format(crate.edition))
 
-def _create_extra_input_args(build_info):
+def _create_extra_input_args(build_info, dep_info):
     """Gather additional input arguments from transitive dependencies
 
     Args:
         build_info (BuildInfo): The BuildInfo provider from the target Crate's set of inputs.
+        dep_info (DepInfo): The Depinfo provider form the target Crate's set of inputs.
 
     Returns:
         tuple: A tuple of the following items:
-            - (list): A list of all build info `OUT_DIR` File objects
+            - (depset[File]): A list of all build info `OUT_DIR` File objects
             - (str): The `OUT_DIR` of the current build info
             - (File): An optional generated environment file from a `cargo_build_script` target
-            - (list): All direct and transitive build flags from the current build info.
+            - (depset[File]): All direct and transitive build flag files from the current build info.
     """
     input_files = []
 
@@ -949,12 +956,17 @@ def _create_extra_input_args(build_info):
     if build_info:
         out_dir = build_info.out_dir.path
         build_env_file = build_info.rustc_env
-        build_flags_files.append(build_info.flags.path)
-        build_flags_files.append(build_info.link_flags.path)
+        build_flags_files.append(build_info.flags)
+        build_flags_files.append(build_info.link_flags)
         input_files.append(build_info.out_dir)
         input_files.append(build_info.link_flags)
 
-    return input_files, out_dir, build_env_file, build_flags_files
+    return (
+        depset(input_files, transitive = [dep_info.link_search_path_files]),
+        out_dir,
+        build_env_file,
+        depset(build_flags_files, transitive = [dep_info.link_search_path_files]),
+    )
 
 def _compute_rpaths(toolchain, output_dir, dep_info):
     """Determine the artifact's rpaths relative to the bazel root for runtime linking of shared libraries.