More robustly detect cargo metadata

gem/exe/rb-sys-dock

@@ -18,7 +18,13 @@ OPTIONS = {
 }
 
 def cargo_metadata
-  @cargo_metadata ||= RbSys::Cargo::Metadata.new("rb-sys-dock", deps: true)
+  return @cargo_metadata if defined?(@cargo_metadata)
+
+  @cargo_metadata = begin
+    RbSys::Cargo::Metadata.inferred(deps: true)
+  rescue
+    nil
+  end
 end
 
 def logger
@@ -421,7 +427,7 @@ def set_env
 end
 
 def lint_rb_sys
-  cargo_version = cargo_metadata.rb_sys_version
+  cargo_version = cargo_metadata&.rb_sys_version || RbSys::VERSION
   return if cargo_version == RbSys::VERSION
   logger.warn("Cargo rb-sys version (#{cargo_version}) does not match Ruby gem version (#{RbSys::VERSION})")
 rescue => e

gem/lib/rb_sys/cargo/metadata.rb

@@ -9,6 +9,26 @@ module Cargo
     class Metadata
       attr_reader :name
 
+      class << self
+        # Infers the Cargo project's name from the Cargo.toml file.
+        #
+        # @return [RbSys::Cargo::Metadata]
+        def inferred(deps: false)
+          new(File.read("Cargo.toml").match(/^name = "(.*)"/)[1], deps: deps)
+        rescue
+          new(File.basename(Dir.pwd), deps: deps)
+        end
+
+        # Initializes a new Cargo::Metadata instance or infers the Cargo project's name.
+        #
+        # @param name [String] the name of the Cargo project
+        def new_or_inferred(name, deps: false)
+          new(name, deps: deps).load!
+        rescue CargoMetadataError
+          inferred
+        end
+      end
+
       # Initializes a new Cargo::Metadata instance.
       #
       # @param name [String] the name of the Cargo project
@@ -92,12 +112,22 @@ def metadata
       end
 
       # Returns the rb-sys version, if any.
+      #
+      # @return [String]
       def rb_sys_version
         pkg = packages.find { |p| p.fetch("name") == "rb-sys" }
         return unless pkg
         pkg["version"]
       end
 
+      # Eagerly run `cargo metadata`, raising a RbSys::CargoCargoMetadataError` if it fails.
+      #
+      # @return [RbSys::Cargo::Metadata]
+      def load!
+        cargo_metadata
+        self
+      end
+
       private
 
       def package_metadata

gem/lib/rb_sys/extensiontask.rb

@@ -57,7 +57,7 @@ def define
     end
 
     def cargo_metadata
-      @cargo_metadata ||= Cargo::Metadata.new(@name)
+      @cargo_metadata ||= Cargo::Metadata.new_or_inferred(@name)
     end
 
     def extconf

gem/test/test_cargo_metadata.rb

@@ -30,6 +30,73 @@ def test_fails_when_cargo_metadata_fails
     end
   end
 
+  def test_load_raises_error_when_cargo_metadata_fails
+    skip if win_target?
+
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        assert_raises(RbSys::CargoMetadataError) do
+          metadata = RbSys::Cargo::Metadata.new("foo")
+          metadata.load!
+        end
+      end
+    end
+  end
+
+  def test_load_returns_self
+    skip if win_target?
+
+    in_new_crate("foo") do |dir|
+      metadata = RbSys::Cargo::Metadata.new("foo")
+
+      assert_equal metadata, metadata.load!
+    end
+  end
+
+  def test_inferred_returns_valid_info
+    skip if win_target?
+
+    in_new_crate("fooyoo") do |dir|
+      metadata = RbSys::Cargo::Metadata.inferred
+
+      assert_equal "fooyoo", metadata.name
+    end
+  end
+
+  def test_inferred_falls_back_to_dir_name
+    skip if win_target?
+
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        metadata = RbSys::Cargo::Metadata.inferred
+
+        assert_equal File.basename(dir), metadata.name
+      end
+    end
+  end
+
+  def test_new_or_inferred_returns_valid_info
+    skip if win_target?
+
+    in_new_crate("foo") do |dir|
+      metadata = RbSys::Cargo::Metadata.new_or_inferred("foofer")
+
+      assert_equal "foofer", metadata.name
+    end
+  end
+
+  def test_new_or_inferred_falls_back_to_inferred
+    skip if win_target?
+
+    Dir.mktmpdir do |dir|
+      Dir.chdir(dir) do
+        metadata = RbSys::Cargo::Metadata.new_or_inferred("foofer")
+
+        assert_equal File.basename(dir), metadata.name
+      end
+    end
+  end
+
   private
 
   def in_new_crate(name, &blk)