vcpkg install: Print install plan and add --dry-run option

toolsrc/src/commands_install.cpp

@@ -12,6 +12,7 @@
 namespace vcpkg::Commands::Install
 {
     using Dependencies::PackageSpecWithInstallPlan;
+    using Dependencies::RequestType;
     using Dependencies::InstallPlanType;
 
     static void install_and_write_listfile(const VcpkgPaths& paths, const BinaryParagraph& bpgh)
@@ -136,6 +137,51 @@ namespace vcpkg::Commands::Install
         return SortedVector<std::string>(std::move(installed_files));
     }
 
+    static void print_plan(const std::vector<PackageSpecWithInstallPlan>& plan)
+    {
+        std::vector<const PackageSpecWithInstallPlan*> already_installed;
+        std::vector<const PackageSpecWithInstallPlan*> build_and_install;
+        std::vector<const PackageSpecWithInstallPlan*> install;
+
+        for (const PackageSpecWithInstallPlan& i : plan)
+        {
+            switch (i.plan.plan_type)
+            {
+                case InstallPlanType::ALREADY_INSTALLED:
+                    already_installed.push_back(&i);
+                    continue;
+                case InstallPlanType::BUILD_AND_INSTALL:
+                    build_and_install.push_back(&i);
+                    continue;
+                case InstallPlanType::INSTALL:
+                    install.push_back(&i);
+                    continue;
+                default:
+                    Checks::unreachable(VCPKG_LINE_INFO);
+            }
+        }
+
+        auto print_lambda = [](const PackageSpecWithInstallPlan* p) { return to_output_string(p->plan.request_type, p->spec.to_string()); };
+
+        if (!already_installed.empty())
+        {
+            std::sort(already_installed.begin(), already_installed.end(), &PackageSpecWithInstallPlan::compare_by_name);
+            System::println("The following packages are already installed:\n%s", Strings::join("\n", already_installed, print_lambda));
+        }
+
+        if (!build_and_install.empty())
+        {
+            std::sort(build_and_install.begin(), build_and_install.end(), &PackageSpecWithInstallPlan::compare_by_name);
+            System::println("The following packages will be built and installed:\n%s", Strings::join("\n", build_and_install, print_lambda));
+        }
+
+        if (!install.empty())
+        {
+            std::sort(install.begin(), install.end(), &PackageSpecWithInstallPlan::compare_by_name);
+            System::println("The following packages will be installed:\n%s", Strings::join("\n", install, print_lambda));
+        }
+    }
+
     void install_package(const VcpkgPaths& paths, const BinaryParagraph& binary_paragraph, StatusParagraphs* status_db)
     {
         const fs::path package_dir = paths.package_dir(binary_paragraph.spec);
@@ -185,6 +231,8 @@ namespace vcpkg::Commands::Install
 
     void perform_and_exit(const VcpkgCmdArguments& args, const VcpkgPaths& paths, const Triplet& default_target_triplet)
     {
+        static const std::string OPTION_DRY_RUN = "--dry-run";
+
         // input sanitization
         static const std::string example = Commands::Help::create_example_string("install zlib zlib:x64-windows curl boost");
         args.check_min_arg_count(1, example);
@@ -196,7 +244,8 @@ namespace vcpkg::Commands::Install
                                     return spec;
                                 });
 
-        args.check_and_get_optional_command_arguments({});
+        const std::unordered_set<std::string> options = args.check_and_get_optional_command_arguments({ OPTION_DRY_RUN });
+        const bool dryRun = options.find(OPTION_DRY_RUN) != options.cend();
 
         // create the plan
         StatusParagraphs status_db = database_load_check(paths);
@@ -212,6 +261,23 @@ namespace vcpkg::Commands::Install
         }
         Metrics::track_property("installplan", specs_string);
 
+        print_plan(install_plan);
+
+        const bool has_non_user_requested_packages = std::find_if(install_plan.cbegin(), install_plan.cend(), [](const PackageSpecWithInstallPlan& package)-> bool
+                                                                  {
+                                                                      return package.plan.request_type != RequestType::USER_REQUESTED;
+                                                                  }) != install_plan.cend();
+
+        if (has_non_user_requested_packages)
+        {
+            System::println(System::Color::warning, "Additional packages (*) need to be installed to complete this operation.");
+        }
+
+        if (dryRun)
+        {
+            Checks::exit_success(VCPKG_LINE_INFO);
+        }
+
         // execute the plan
         for (const PackageSpecWithInstallPlan& action : install_plan)
         {