Make sure to force latest resolvable version explicitly

To make sure we can always update to the latest resolvable version for
each gem explicitly requested for update, we first run a full update,
and then add explicit exact requirements to the resolved versions. This
may lead into conflicts, but our resolver already automatically parses
those and unlocks additional gems to fix them.

bundler/lib/bundler/definition.rb

@@ -568,7 +568,9 @@ def resolution_packages
         last_resolve = converge_locked_specs
         remove_invalid_platforms!(current_dependencies)
         packages = Resolver::Base.new(source_requirements, expanded_dependencies, last_resolve, @platforms, locked_specs: @originally_locked_specs, unlock: @gems_to_unlock, prerelease: gem_version_promoter.pre?)
-        additional_base_requirements_for_resolve(packages, last_resolve)
+        packages = additional_base_requirements_to_prevent_downgrades(packages, last_resolve)
+        packages = additional_base_requirements_to_force_updates(packages)
+        packages
       end
     end
 
@@ -1015,7 +1017,7 @@ def lockfiles_equal?(current, proposed, preserve_unknown_sections)
       current == proposed
     end
 
-    def additional_base_requirements_for_resolve(resolution_packages, last_resolve)
+    def additional_base_requirements_to_prevent_downgrades(resolution_packages, last_resolve)
       return resolution_packages unless @locked_gems && !sources.expired_sources?(@locked_gems.sources)
       converge_specs(@originally_locked_specs - last_resolve).each do |locked_spec|
         next if locked_spec.source.is_a?(Source::Path)
@@ -1024,6 +1026,26 @@ def additional_base_requirements_for_resolve(resolution_packages, last_resolve)
       resolution_packages
     end
 
+    def additional_base_requirements_to_force_updates(resolution_packages)
+      return resolution_packages if @explicit_unlocks.empty?
+
+      unlocked_definition = self.class.new(@lockfile, @dependencies, @sources, true, @ruby_version, @optional_groups, @gemfiles)
+      unlocked_definition.resolution_mode = { "local" => !@remote }
+      unlocked_definition.setup_sources_for_resolve
+      unlocked_definition.gem_version_promoter.tap do |gvp|
+        gvp.level = gem_version_promoter.level
+        gvp.strict = gem_version_promoter.strict
+        gvp.pre = gem_version_promoter.pre
+      end
+      full_update = unlocked_definition.resolve
+
+      @explicit_unlocks.each do |name|
+        version = full_update[name].first&.version
+        resolution_packages.base_requirements[name] = Gem::Requirement.new("= #{version}") if version
+      end
+      resolution_packages
+    end
+
     def remove_invalid_platforms!(dependencies)
       return if Bundler.frozen_bundle?
 

bundler/spec/commands/lock_spec.rb

@@ -252,6 +252,128 @@
     expect(read_lockfile).to eq(remove_checksums_from_lockfile(@lockfile, "(2.3.2)", "(#{rake_version})"))
   end
 
+  it "updates specific gems using --update, even if that requires unlocking other top level gems" do
+    build_repo4 do
+      build_gem "prism", "0.15.1"
+      build_gem "prism", "0.24.0"
+
+      build_gem "ruby-lsp", "0.12.0" do |s|
+        s.add_dependency "prism", "< 0.24.0"
+      end
+
+      build_gem "ruby-lsp", "0.16.1" do |s|
+        s.add_dependency "prism", ">= 0.24.0"
+      end
+
+      build_gem "tapioca", "0.11.10" do |s|
+        s.add_dependency "prism", "< 0.24.0"
+      end
+
+      build_gem "tapioca", "0.13.1" do |s|
+        s.add_dependency "prism", ">= 0.24.0"
+      end
+    end
+
+    gemfile <<~G
+      source "#{file_uri_for(gem_repo4)}"
+
+      gem "tapioca"
+      gem "ruby-lsp"
+    G
+
+    lockfile <<~L
+      GEM
+        remote: #{file_uri_for(gem_repo4)}
+        specs:
+          prism (0.15.1)
+          ruby-lsp (0.12.0)
+            prism (< 0.24.0)
+          tapioca (0.11.10)
+            prism (< 0.24.0)
+
+      PLATFORMS
+        #{lockfile_platforms}
+
+      DEPENDENCIES
+        ruby-lsp
+        tapioca
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+
+    bundle "lock --update tapioca --verbose"
+
+    expect(lockfile).to include("tapioca (0.13.1)")
+  end
+
+  it "updates specific gems using --update, even if that requires unlocking other top level gems, but only as few as possible" do
+    build_repo4 do
+      build_gem "prism", "0.15.1"
+      build_gem "prism", "0.24.0"
+
+      build_gem "ruby-lsp", "0.12.0" do |s|
+        s.add_dependency "prism", "< 0.24.0"
+      end
+
+      build_gem "ruby-lsp", "0.16.1" do |s|
+        s.add_dependency "prism", ">= 0.24.0"
+      end
+
+      build_gem "tapioca", "0.11.10" do |s|
+        s.add_dependency "prism", "< 0.24.0"
+      end
+
+      build_gem "tapioca", "0.13.1" do |s|
+        s.add_dependency "prism", ">= 0.24.0"
+      end
+
+      build_gem "other-prism-dependent", "1.0.0" do |s|
+        s.add_dependency "prism", ">= 0.15.1"
+      end
+
+      build_gem "other-prism-dependent", "1.1.0" do |s|
+        s.add_dependency "prism", ">= 0.15.1"
+      end
+    end
+
+    gemfile <<~G
+      source "#{file_uri_for(gem_repo4)}"
+
+      gem "tapioca"
+      gem "ruby-lsp"
+      gem "other-prism-dependent"
+    G
+
+    lockfile <<~L
+      GEM
+        remote: #{file_uri_for(gem_repo4)}
+        specs:
+          other-prism-dependent (1.0.0)
+            prism (>= 0.15.1)
+          prism (0.15.1)
+          ruby-lsp (0.12.0)
+            prism (< 0.24.0)
+          tapioca (0.11.10)
+            prism (< 0.24.0)
+
+      PLATFORMS
+        #{lockfile_platforms}
+
+      DEPENDENCIES
+        ruby-lsp
+        tapioca
+
+      BUNDLED WITH
+         #{Bundler::VERSION}
+    L
+
+    bundle "lock --update tapioca"
+
+    expect(lockfile).to include("tapioca (0.13.1)")
+    expect(lockfile).to include("other-prism-dependent (1.0.0)")
+  end
+
   it "preserves unknown checksum algorithms" do
     lockfile @lockfile.gsub(/(sha256=[a-f0-9]+)$/, "constant=true,\\1,xyz=123")