Exfiltrate more linker flags with get_rust_ldflags.py

BUILD.gn

@@ -20,6 +20,12 @@ config("deno_config") {
   if (is_debug) {
     defines = [ "DEBUG" ]
   }
+  if (is_mac) {
+    libs = [ "resolv" ]
+  }
+  if (is_win) {
+    libs = [ "userenv.lib" ]
+  }
 }
 
 rust_executable("deno") {

build_extra/rust/get_rustc_default_libs.py → build_extra/rust/get_rust_ldflags.py

@@ -64,13 +64,51 @@ def main():
         os.close(argsfile_fd)
         os.unlink(argsfile_path)
 
-    # Write all linker inputs that are dependencies to stdout.
-    # Note that in addition to all .rlib files, we also capture a file named
-    # `crate_name.crate.allocator.rcgu.o`, which contains the implementation
-    # of `__rust_malloc()`, `__rust_free()` etc.
+    # From the list of captured linker arguments, build a list of ldflags that
+    # we actually need.
+    ldflags = []
+    next_arg_is_flag_value = False
     for arg in args:
-        if arg.endswith(".rlib") or arg.endswith(".crate.allocator.rcgu.o"):
-            print(arg)
+        # Note that within the following if/elif blocks, `pass` means `arg`
+        # gets included in `ldflags`. The final `else` clause filters out
+        # unrecognized/unwanted flags.
+        if next_arg_is_flag_value:
+            # We're looking at a value that follows certain parametric flags,
+            # e.g. the path in '-L <path>'.
+            next_arg_is_flag_value = False
+        elif arg.endswith(".rlib"):
+            # Built-in Rust library, e.g. `libstd-8524caae8408aac2.rlib`.
+            pass
+        elif arg.endswith(".crate.allocator.rcgu.o"):
+            # This file is needed because it contains certain allocator
+            # related symbols (e.g. `__rust_alloc`, `__rust_oom`).
+            # The Rust compiler normally generates this file just before
+            # linking an executable. We pass `-Csave-temps` to rustc so it
+            # doesn't delete the file when it's done linking.
+            pass
+        elif arg.endswith(".lib") and not arg.startswith("msvcrt"):
+            # Include most Windows static/import libraries (e.g. `ws2_32.lib`).
+            # However we exclude Rusts choice of C runtime (mvcrt*.lib), since
+            # it makes poor choices.
+            pass
+        elif arg == "-l" or arg == "-L":
+            # `-l <name>`: Link with library (GCC style).
+            # `-L <path>`: Linker search path (GCC style).
+            next_arg_is_flag_value = True  # Ensure flag argument is captured.
+        elif arg == "-Wl,--start-group" or arg == "-Wl,--end-group":
+            # Start or end of an archive group (GCC style).
+            pass
+        elif arg.upper().startswith("/LIBPATH:"):
+            # `/LIBPATH:<path>`: Linker search path (Microsoft style).
+            pass
+        else:
+            # No matches -- don't add this flag to ldflags.
+            continue
+
+        ldflags += [arg]
+
+    # Write the filtered ldflags to stdout, separated by newline characters.
+    sys.stdout.write("\n".join(ldflags))
 
 
 if __name__ == '__main__':

build_extra/rust/rust.gni

@@ -1,20 +1,12 @@
 empty_rs_path = rebase_path("empty.rs", root_build_dir)
-rust_default_libs_bin =
-    exec_script("get_rustc_default_libs.py", [ empty_rs_path ], "list lines")
-rust_default_libs_test = exec_script("get_rustc_default_libs.py",
-                                     [
-                                       empty_rs_path,
-                                       "--test",
-                                     ],
-                                     "list lines")
-
-rust_required_system_libs = []
-if (current_os == "mac") {
-  rust_required_system_libs += [ "resolv" ]
-}
-if (current_os == "win") {
-  rust_required_system_libs += [ "userenv.lib" ]
-}
+rust_bin_ldflags =
+    exec_script("get_rust_ldflags.py", [ empty_rs_path ], "list lines")
+rust_test_ldflags = exec_script("get_rust_ldflags.py",
+                                [
+                                  empty_rs_path,
+                                  "--test",
+                                ],
+                                "list lines")
 
 declare_args() {
   # Absolute path of rust build files.
@@ -186,7 +178,6 @@ template("rust_staticlib") {
                              "testonly",
                            ])
     crate_type = "staticlib"
-    libs = rust_required_system_libs
   }
 }
 
@@ -203,13 +194,11 @@ template("rust_executable") {
     forward_variables_from(invoker, "*")
 
     if (defined(is_test) && is_test) {
-      ldflags = rust_default_libs_test
+      ldflags = rust_test_ldflags
     } else {
-      ldflags = rust_default_libs_bin
+      ldflags = rust_bin_ldflags
     }
 
-    libs = rust_required_system_libs
-
     if (!defined(deps)) {
       deps = []
     }