Revamp CmakeBuilder to fix the issues described in #8572. Specifically:

* Correctly pass command line arguments to CMake
* Call CMake twice - once to configure a project and a second time to build (which is the standard way to use CMake). This fixes the previously incorrect assumption that CMake generates a Make file.
* Update the tests to specify a CMake minimum version of 3.26 (which is already two years old). 3.26 is a bit arbritary but it aligns with Rice, and updates from the ancient 3.5 version being used (which CMake generates a warning message saying stop using it!)
* Update the CMake call to use CMAKE_RUNTIME_OUTPUT_DIRECTORY and CMAKE_LIBRARY_OUTPUT_DIRECTORY to tell CMake to copy compiled binaries to the a Gem's lib directory.

Note the updated builder took inspiration from the Cargo Builder, meaning you first create an instance of CmakeBuilder versus just calling class methods.

Author: cfisoi

lib/rubygems/ext/builder.rb

@@ -165,7 +165,7 @@ def builder_for(extension) # :nodoc:
       @ran_rake = true
       Gem::Ext::RakeBuilder
     when /CMakeLists.txt/ then
-      Gem::Ext::CmakeBuilder
+      Gem::Ext::CmakeBuilder.new
     when /Cargo.toml/ then
       Gem::Ext::CargoBuilder.new
     else

lib/rubygems/ext/cmake_builder.rb

@@ -1,21 +1,114 @@
 # frozen_string_literal: true
 
+# This builder creates extensions defined using CMake. Its is invoked if a Gem's spec file
+# sets the `extension` property to a string that contains `CMakeLists.txt`.
+#
+# In general, CMake projects are built in two steps:
+#
+#  * configure
+#  * build
+#
+# The builder follow this convention. First it runs a configuration step and then it runs a build step.
+#
+# CMake projects can be quite configurable - it is likely you will want to specify options when
+# installing a gem. To pass options to CMake specify them after `--` in the gem install command. For example:
+#
+#   gem install <gem_name> -- --preset <preset_name>
+#
+# Note that options are ONLY sent to the configure step - it is not currently possible to specify
+# options for the build step. If this becomes and issue then the CMake builder can be updated to
+# support build options.
+#
+# Useful options to know are:
+#
+#  -G to specify a generator (-G Ninja is recommended)
+#  -D<CMAKE_VARIABLE> to set a CMake variable (for example -DCMAKE_BUILD_TYPE=Release)
+#  --preset <preset_name> to use a preset
+#
+# If the Gem author provides presets, via CMakePresets.json file, you will likely want to us use one of them.
+# If not, then you may wish to specify a generator (Ninja is recommended since it can build projects in parallel
+# versus a Make generator which build ins serial and thus is *much* slower).
+
+require "fileutils"
+
 class Gem::Ext::CmakeBuilder < Gem::Ext::Builder
-  def self.build(extension, dest_path, results, args=[], lib_dir=nil, cmake_dir=Dir.pwd,
-    target_rbconfig=Gem.target_rbconfig)
+  attr_accessor :runner, :profile
+
+  def initialize
+    @runner = self.class.method(:run)
+    @profile = :release
+  end
+
+  def build(extension, gem_dir, results, args = [], lib_dir = nil, cmake_dir = Dir.pwd, target_rbconfig = Gem.target_rbconfig)
     if target_rbconfig.path
       warn "--target-rbconfig is not yet supported for CMake extensions. Ignoring"
     end
 
-    unless File.exist?(File.join(cmake_dir, "Makefile"))
-      require_relative "../command"
-      cmd = ["cmake", ".", "-DCMAKE_INSTALL_PREFIX=#{dest_path}", *Gem::Command.build_args]
+    # Make sure lib dir is set
+    lib_dir ||= File.join(gem_dir, "lib")
 
-      run cmd, results, class_name, cmake_dir
-    end
+    # Figure the build dir
+    build_dir = File.join(cmake_dir, "build")
 
-    make dest_path, results, cmake_dir, target_rbconfig: target_rbconfig
+    # Check if the gem defined presets
+    check_presets(cmake_dir, args)
+
+    # Configure
+    configure(cmake_dir, build_dir, lib_dir, args, results)
+
+    # Compile
+    compile(cmake_dir, build_dir, args, results)
 
     results
   end
+
+  def configure(cmake_dir, build_dir, lib_dir, args, results)
+    cmd = ["cmake",
+           cmake_dir,
+           "-B",
+           build_dir,
+           "-DCMAKE_RUNTIME_OUTPUT_DIRECTORY=#{lib_dir}", # Windows
+           "-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=#{lib_dir}", # Not Windows
+           *Gem::Command.build_args,
+           *args]
+
+    runner.call(cmd, results, "cmake", cmake_dir)
+  end
+
+  def compile(cmake_dir, build_dir, args, results)
+    cmd = ["cmake",
+           "--build",
+           build_dir.to_s,
+           "--config",
+           @profile.to_s]
+    runner.call(cmd, results, "cmake", cmake_dir)
+  end
+
+  private
+
+  def check_presets(cmake_dir, args)
+    # Return if the user specified a preset
+    return unless args.grep(/--preset/i).empty?
+
+    cmd = ["cmake",
+           "--list-presets"]
+
+    begin
+      require "open3"
+      build_env = { "SOURCE_DATE_EPOCH" => Gem.source_date_epoch_string }
+      stdout, _, _ = Open3.capture3(build_env, *cmd, chdir: cmake_dir)
+      message = <<~EOS
+        The gem author provided a list of presets that can be used to build the gem. To use a preset specify it on the command line:
+
+          gem install <gem_name> -- --preset <preset_name>
+
+        #{stdout}
+      EOS
+
+      STDOUT << message << "\n"
+      STDOUT.flush
+    rescue Gem::InstallError
+      # Do nothing, CMakePresets.json was not included in the Gem
+    end
+  end
 end

test/rubygems/test_gem_ext_cmake_builder.rb

@@ -29,7 +29,7 @@ def setup
   def test_self_build
     File.open File.join(@ext, "CMakeLists.txt"), "w" do |cmakelists|
       cmakelists.write <<-EO_CMAKE
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.26)
 project(self_build NONE)
 install (FILES test.txt DESTINATION bin)
       EO_CMAKE
@@ -39,46 +39,47 @@ def test_self_build
 
     output = []
 
-    Gem::Ext::CmakeBuilder.build nil, @dest_path, output, [], nil, @ext
+    builder = Gem::Ext::CmakeBuilder.new
+    builder.build nil, @dest_path, output, [], nil, @ext
 
     output = output.join "\n"
 
-    assert_match(/^cmake \. -DCMAKE_INSTALL_PREFIX\\=#{Regexp.escape @dest_path}/, output)
+    assert_match(/^current directory: #{Regexp.escape @ext}/, output)
+    assert_match(/cmake.*-DCMAKE_RUNTIME_OUTPUT_DIRECTORY\\=#{Regexp.escape @dest_path}/, output)
+    assert_match(/cmake.*-DCMAKE_LIBRARY_OUTPUT_DIRECTORY\\=#{Regexp.escape @dest_path}/, output)
     assert_match(/#{Regexp.escape @ext}/, output)
-    assert_contains_make_command "", output
-    assert_contains_make_command "install", output
-    assert_match(/test\.txt/, output)
   end
 
   def test_self_build_fail
     output = []
 
+    builder = Gem::Ext::CmakeBuilder.new
     error = assert_raise Gem::InstallError do
-      Gem::Ext::CmakeBuilder.build nil, @dest_path, output, [], nil, @ext
+      builder.build nil, @dest_path, output, [], nil, @ext
     end
 
     output = output.join "\n"
-
-    shell_error_msg = /(CMake Error: .*)/
-
-    assert_match "cmake failed", error.message
-
-    assert_match(/^cmake . -DCMAKE_INSTALL_PREFIX\\=#{Regexp.escape @dest_path}/, output)
-    assert_match(/#{shell_error_msg}/, output)
+    assert_match(/CMake Error: .*/, output)
   end
 
   def test_self_build_has_makefile
-    File.open File.join(@ext, "Makefile"), "w" do |makefile|
-      makefile.puts "all:\n\t@echo ok\ninstall:\n\t@echo ok"
+    File.open File.join(@ext, "CMakeLists.txt"), "w" do |cmakelists|
+      cmakelists.write <<-EO_CMAKE
+cmake_minimum_required(VERSION 3.26)
+project(self_build NONE)
+install (FILES test.txt DESTINATION bin)
+      EO_CMAKE
     end
 
     output = []
 
-    Gem::Ext::CmakeBuilder.build nil, @dest_path, output, [], nil, @ext
+    builder = Gem::Ext::CmakeBuilder.new
+    builder.build nil, @dest_path, output, [], nil, @ext
 
     output = output.join "\n"
 
-    assert_contains_make_command "", output
-    assert_contains_make_command "install", output
+    # The default generator will create a Makefile in the build directory
+    makefile = File.join(@ext, "build", "Makefile")
+    assert(File.exist?(makefile))
   end
 end