build: support rust crates that generate sources in their build script

build_extra/rust/run.py

@@ -7,6 +7,7 @@
 import os
 import re
 
+args = sys.argv[1:]
 env = os.environ.copy()
 
 if sys.platform == 'win32':
@@ -26,9 +27,19 @@
 env["GN_OUT_DIR"] = os.path.abspath(".")
 assert os.path.isdir(env["GN_OUT_DIR"])
 
+# Some crates (e.g. 'typenum') generate source files and place them in the
+# directory indicated by the 'OUT_DIR' environment variable, which is normally
+# set by Cargo. We pre-generate these files and store them in the source repo.
+# Therefore, set 'OUT_DIR' so these crates can find their generated sources.
+for i, arg in enumerate(args):
+    match = re.search('--generated-source-dir=(.*)', arg)
+    if match:
+        env["OUT_DIR"] = os.path.abspath(match.group(1))
+        del args[i]
+        break
+
 # Set the CARGO_PKG_VERSION env variable if provided as an argument
 # When building with Cargo this variable is set automatically
-args = sys.argv[1:]
 for i, arg in enumerate(args):
     match = re.search('--cargo-pkg-version="?([^"]*)"?', arg)
     if match:

build_extra/rust/rust.gni

@@ -62,8 +62,9 @@ template("_rust_crate") {
                            "crate_version",
                            "deps",
                            "edition",
-                           "inputs",
                            "features",
+                           "generated_source_dir",
+                           "inputs",
                            "is_test",
                            "libs",
                            "source_root",
@@ -237,6 +238,17 @@ template("_rust_crate") {
       "--color=always",
     ]
 
+    if (defined(generated_source_dir)) {
+      args += [
+        # Some crates (e.g. 'typenum') generate source files and place them in
+        # the directory indicated by the 'OUT_DIR' environment variable, which
+        # is normally set by Cargo. This flag tells run.py to set 'OUT_DIR' to
+        # the path where the current crate can find its generated sources.
+        "--generated-source-dir=" +
+            rebase_path(generated_source_dir, root_build_dir),
+      ]
+    }
+
     if (defined(crate_version)) {
       args += [
         # This is used to set env variables for Cargo build compatibility