BindingsGenerator+CMake: Keep track of IDL dependencies

This commit teaches BindingsGenerator to generate depfiles, which can be
used by CMake to ensure that bindings are properly regenerated when
imported IDL files change.

Two new options, `--depfile` and `--depfile-target` are added.
- `--depfile` sets the path for the dependency file.
- `--depfile-target` lets us set a target name different than the output
  file in the depfile. This option is needed because generated files are
  first written to a temporary file, but depfiles have to refer to the
  final location.
These are analogous to GCC's `-MF` and `-MT` options respectively. The
depfile's syntax matches the ones generated by GCC.

Note: This changes the minimal required CMake version to 3.20 if the
Make generator is used, and to 3.21 for the Xcode generator. Ninja is
not affected.

Meta/CMake/common_options.cmake

@@ -2,6 +2,11 @@
 # Options common for the Serenity (target) and Lagom (host) builds
 #
 
+# Make relative paths in depfiles be relative to CMAKE_CURRENT_BINARY_DIR rather than to CMAKE_BINARY_DIR
+if (POLICY CMP0116)
+    cmake_policy(SET CMP0116 NEW)
+endif()
+
 serenity_option(ENABLE_COMPILETIME_FORMAT_CHECK ON CACHE BOOL "Enable compiletime format string checks")
 serenity_option(ENABLE_UNDEFINED_SANITIZER OFF CACHE BOOL "Enable undefined behavior sanitizer testing in gcc/clang")
 

Meta/CMake/libweb_generators.cmake

@@ -111,14 +111,27 @@ function (generate_js_bindings target)
             list(GET BINDINGS_TYPES ${iter} bindings_type)
             get_property(include_paths DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY INCLUDE_DIRECTORIES)
             list(TRANSFORM include_paths PREPEND -i)
+
+            # Ninja expects the target name in depfiles to be relative to CMAKE_BINARY_DIR, but ${bindings_src} is
+            # relative to CMAKE_CURRENT_BINARY_DIR. CMake >= 3.20 can do the rewriting transparently (CMP0116).
+            if(CMAKE_GENERATOR MATCHES "^Ninja" AND NOT POLICY CMP0116)
+                # FIXME: Drop this branch for cmake_minimum_required(3.20)
+                get_filename_component(full_path ${bindings_src} ABSOLUTE BASE_DIR ${CMAKE_CURRENT_BINARY_DIR})
+                file(RELATIVE_PATH depfile_target ${CMAKE_BINARY_DIR} ${full_path})
+            else()
+                set(depfile_target ${bindings_src})
+            endif()
+
             add_custom_command(
                 OUTPUT "${bindings_src}"
-                COMMAND "$<TARGET_FILE:Lagom::BindingsGenerator>" "--${bindings_type}" -o "${bindings_src}.tmp" ${include_paths} "${LIBWEB_INPUT_FOLDER}/${class}.idl" "${LIBWEB_INPUT_FOLDER}"
+                COMMAND "$<TARGET_FILE:Lagom::BindingsGenerator>" "--${bindings_type}" -o "${bindings_src}.tmp" --depfile "${bindings_src}.d"
+                        --depfile-target "${depfile_target}" ${include_paths} "${LIBWEB_INPUT_FOLDER}/${class}.idl" "${LIBWEB_INPUT_FOLDER}"
                 COMMAND "${CMAKE_COMMAND}" -E copy_if_different "${bindings_src}.tmp" "${bindings_src}"
                 COMMAND "${CMAKE_COMMAND}" -E remove "${bindings_src}.tmp"
                 VERBATIM
                 DEPENDS Lagom::BindingsGenerator
                 MAIN_DEPENDENCY ${class}.idl
+                DEPFILE ${CMAKE_CURRENT_BINARY_DIR}/${bindings_src}.d
             )
         endforeach()
 

Meta/Lagom/Tools/CodeGenerators/LibWeb/BindingsGenerator/main.cpp

@@ -33,6 +33,8 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     StringView path;
     StringView import_base_path;
     StringView output_path = "-"sv;
+    StringView depfile_path;
+    StringView depfile_target;
     bool constructor_header_mode = false;
     bool constructor_implementation_mode = false;
     bool prototype_header_mode = false;
@@ -57,6 +59,8 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         },
     });
     args_parser.add_option(output_path, "Path to output generated file into", "output-path", 'o', "output-path");
+    args_parser.add_option(depfile_path, "Path to write dependency file to", "depfile", 'd', "depfile-path");
+    args_parser.add_option(depfile_target, "Name of target in the depfile (default: output path)", "depfile-target", 't', "target");
     args_parser.add_positional_argument(path, "IDL file", "idl-file");
     args_parser.add_positional_argument(import_base_path, "Import base path", "import-base-path", Core::ArgsParser::Required::No);
     args_parser.parse(arguments);
@@ -66,7 +70,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     LexicalPath lexical_path(path);
     auto& namespace_ = lexical_path.parts_view().at(lexical_path.parts_view().size() - 2);
 
-    auto data = TRY(file->read_all());
+    auto data = TRY(file->read_until_eof());
 
     if (import_base_path.is_null())
         import_base_path = lexical_path.dirname();
@@ -146,5 +150,19 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
         IDL::generate_iterator_prototype_implementation(interface, output_builder);
 
     TRY(output_file->write(output_builder.string_view().bytes()));
+
+    if (!depfile_path.is_null()) {
+        auto depfile = TRY(Core::Stream::File::open_file_or_standard_stream(depfile_path, Core::Stream::OpenMode::Write));
+
+        StringBuilder depfile_builder;
+        depfile_builder.append(depfile_target.is_null() ? output_path : depfile_target);
+        depfile_builder.append(':');
+        for (auto const& path : parser.imported_files()) {
+            depfile_builder.append(" \\\n "sv);
+            depfile_builder.append(path);
+        }
+        depfile_builder.append('\n');
+        TRY(depfile->write(depfile_builder.string_view().bytes()));
+    }
     return 0;
 }

Userland/Libraries/LibIDL/IDLParser.cpp

@@ -1068,4 +1068,8 @@ HashTable<NonnullOwnPtr<Interface>>& Parser::top_level_interfaces()
     return top_level_parser()->interfaces;
 }
 
+Vector<DeprecatedString> Parser::imported_files() const
+{
+    return const_cast<Parser*>(this)->top_level_resolved_imports().keys();
+}
 }

Userland/Libraries/LibIDL/IDLParser.h

@@ -20,6 +20,8 @@ public:
     Parser(DeprecatedString filename, StringView contents, DeprecatedString import_base_path);
     Interface& parse();
 
+    Vector<DeprecatedString> imported_files() const;
+
 private:
     // https://webidl.spec.whatwg.org/#dfn-special-operation
     // A special operation is a getter, setter or deleter.