7 files changed, 33 insertions, 12 deletions
diff --git a/lib/rubygems/ext/cargo_builder.rb b/lib/rubygems/ext/cargo_builder.rb
index 7c1d4a72cd..2a9e72fdfe 100644
--- a/lib/rubygems/ext/cargo_builder.rb
+++ b/lib/rubygems/ext/cargo_builder.rb
@@ -14,7 +14,7 @@ class Gem::Ext::CargoBuilder < Gem::Ext::Builder
     @profile = :release
   end
 
-  def build(_extension, dest_path, results, args = [], lib_dir = nil, cargo_dir = Dir.pwd)
+  def build(extension, dest_path, results, args = [], lib_dir = nil, cargo_dir = Dir.pwd)
     require "tempfile"
     require "fileutils"
 
@@ -43,16 +43,19 @@ class Gem::Ext::CargoBuilder < Gem::Ext::Builder
       dlext_path = File.join(File.dirname(dylib_path), dlext_name)
       FileUtils.cp(dylib_path, dlext_path)
 
+      nesting = extension_nesting(extension)
+
       # TODO: remove in RubyGems 4
       if Gem.install_extension_in_lib && lib_dir
-        FileUtils.mkdir_p lib_dir
-        p [dlext_path, lib_dir]
-        FileUtils.cp_r dlext_path, lib_dir, remove_destination: true
+        nested_lib_dir = File.join(lib_dir, nesting)
+        FileUtils.mkdir_p nested_lib_dir
+        FileUtils.cp_r dlext_path, nested_lib_dir, remove_destination: true
       end
 
       # move to final destination
-      FileUtils.mkdir_p dest_path
-      FileUtils.cp_r dlext_path, dest_path, remove_destination: true
+      nested_dest_path = File.join(dest_path, nesting)
+      FileUtils.mkdir_p nested_dest_path
+      FileUtils.cp_r dlext_path, nested_dest_path, remove_destination: true
     ensure
       # clean up intermediary build artifacts
       FileUtils.rm_rf tmp_dest if tmp_dest
@@ -94,6 +97,23 @@ class Gem::Ext::CargoBuilder < Gem::Ext::Builder
     ENV.fetch("CARGO", "cargo")
   end
 
+  # returns the directory nesting of the extension, ignoring the first part, so
+  # "ext/foo/bar/Cargo.toml" becomes "foo/bar"
+  def extension_nesting(extension)
+    parts = extension.to_s.split(Regexp.union([File::SEPARATOR, File::ALT_SEPARATOR].compact))
+
+    parts = parts.each_with_object([]) do |segment, final|
+      next if segment == "."
+      if segment == ".."
+        raise Gem::InstallError, "extension outside of gem root" if final.empty?
+        next final.pop
+      end
+      final << segment
+    end
+
+    File.join(parts[1...-1])
+  end
+
   def rb_config_env
     result = {}
     RbConfig::CONFIG.each {|k, v| result["RBCONFIG_#{k}"] = v }
diff --git a/test/rubygems/test_gem_ext_cargo_builder.rb b/test/rubygems/test_gem_ext_cargo_builder.rb
index 5ffe5f0b6f..df50150d50 100644
--- a/test/rubygems/test_gem_ext_cargo_builder.rb
+++ b/test/rubygems/test_gem_ext_cargo_builder.rb
@@ -32,7 +32,7 @@ class TestGemExtCargoBuilder < Gem::TestCase
     Dir.chdir @ext do
       ENV.update(@rust_envs)
       builder = Gem::Ext::CargoBuilder.new
-      builder.build nil, @dest_path, output
+      builder.build "Cargo.toml", @dest_path, output
     end
 
     output = output.join "\n"
@@ -58,7 +58,7 @@ class TestGemExtCargoBuilder < Gem::TestCase
     Dir.chdir @ext do
       ENV.update(@rust_envs)
       builder = Gem::Ext::CargoBuilder.new
-      builder.build nil, @dest_path, output
+      builder.build "Cargo.toml", @dest_path, output
     end
 
     output = output.join "\n"
@@ -83,7 +83,7 @@ class TestGemExtCargoBuilder < Gem::TestCase
       Dir.chdir @ext do
         ENV.update(@rust_envs)
         builder = Gem::Ext::CargoBuilder.new
-        builder.build nil, @dest_path, []
+        builder.build "Cargo.toml", @dest_path, []
       end
     end
 
@@ -130,7 +130,7 @@ class TestGemExtCargoBuilder < Gem::TestCase
         Open3.capture2e(*gem, "install", "--verbose", "--local", built_gem, *ARGV)
       end
 
-      stdout_and_stderr_str, status = Open3.capture2e(env_for_subprocess, *ruby_with_rubygems_in_load_path, "-rcustom_name_ext", "-e", "puts 'Result: ' + CustomName.say_hello")
+      stdout_and_stderr_str, status = Open3.capture2e(env_for_subprocess, *ruby_with_rubygems_in_load_path, "-rcustom_name", "-e", "puts 'Result: ' + CustomName.say_hello")
 
       assert status.success?, stdout_and_stderr_str
       assert_match "Result: Hello world!", stdout_and_stderr_str
diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/custom_name.gemspec b/test/rubygems/test_gem_ext_cargo_builder/custom_name/custom_name.gemspec
index 95332ec84f..43dddac243 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/custom_name/custom_name.gemspec
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/custom_name.gemspec
@@ -2,7 +2,7 @@ Gem::Specification.new do |s|
   s.name          = "custom_name"
   s.version       = "0.1.0"
   s.summary       = "A Rust extension for Ruby"
-  s.extensions    = ["Cargo.toml"]
+  s.extensions    = ["ext/custom_name_lib/Cargo.toml"]
   s.authors       = ["Ian Ker-Seymer"]
-  s.files         = ["Cargo.toml", "Cargo.lock", "src/lib.rs"]
+  s.files         = ["lib/custom_name.rb", "ext/custom_name_lib/Cargo.toml", "ext/custom_name_lib/Cargo.lock", "ext/custom_name_lib/src/lib.rs"]
 end
diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/Cargo.lock b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.lock
index 25905d8cf6..25905d8cf6 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/custom_name/Cargo.lock
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.lock
diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/Cargo.toml b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.toml
index 0777be730e..0777be730e 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/custom_name/Cargo.toml
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/Cargo.toml
diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/src/lib.rs b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/src/lib.rs
index 28ba3be564..28ba3be564 100644
--- a/test/rubygems/test_gem_ext_cargo_builder/custom_name/src/lib.rs
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/ext/custom_name_lib/src/lib.rs
diff --git a/test/rubygems/test_gem_ext_cargo_builder/custom_name/lib/custom_name.rb b/test/rubygems/test_gem_ext_cargo_builder/custom_name/lib/custom_name.rb
new file mode 100644
index 0000000000..5ae8b00a5f
--- /dev/null
+++ b/test/rubygems/test_gem_ext_cargo_builder/custom_name/lib/custom_name.rb
@@ -0,0 +1 @@
+require "custom_name_lib/custom_name_ext"