Migrate ipr/impl and ipr/utility-impl to C++20 module cxx.ipr.impl

CMakeLists.txt

@@ -30,7 +30,6 @@ add_library(${PROJECT_NAME}
    src/cxx-ipr-io.cxx
    src/cxx-ipr-traversal.cxx
    src/input.cxx
-   src/utility.cxx
    src/cxx-ipr.cxx
 )
 
@@ -42,6 +41,7 @@ target_sources(${PROJECT_NAME}
          src/cxx-ipr.ixx
          src/cxx-ipr-traversal.ixx
          src/cxx-ipr-io.ixx
+         src/cxx-ipr-impl.ixx
 )
 
 target_include_directories(${PROJECT_NAME}
@@ -51,10 +51,8 @@ target_include_directories(${PROJECT_NAME}
 
 target_sources(${PROJECT_NAME}
     PRIVATE
-        ${PROJECT_SOURCE_DIR}/include/ipr/impl
         ${PROJECT_SOURCE_DIR}/include/ipr/lexer
         ${PROJECT_SOURCE_DIR}/include/ipr/node-category
-        ${PROJECT_SOURCE_DIR}/include/ipr/utility-impl
         ${PROJECT_SOURCE_DIR}/include/ipr/input
         ${PROJECT_SOURCE_DIR}/3rdparty/doctest/doctest.h
 )

include/ipr/std-preamble

@@ -4,18 +4,15 @@
 // Written by Gabriel Dos Reis.
 // See LICENSE for copyright and license notices.
 //
-// Standard library preamble for translation units that use `import cxx.ipr;`
-// followed by `#include <ipr/impl>` (or other IPR project headers).
+// Standard library preamble for IPR module interface and implementation units.
+// This header is included in the global module fragment of IPR .ixx and .cxx
+// files to ensure standard library headers are available before the module
+// purview begins.
 //
-// TEMPORARY: This header exists because the implementation layer (<ipr/impl>)
-// is not yet modularized.  MSVC requires all standard #includes to appear
-// before `import cxx.ipr;` to avoid redefinition errors.  Once <ipr/impl>
-// becomes a module, this preamble is no longer needed.
-//
-// Usage:
+// Usage (in a module interface or implementation unit):
+//     module;
 //     #include <ipr/std-preamble>
-//     import cxx.ipr;
-//     #include <ipr/impl>
+//     export module cxx.ipr.impl;   // or: module cxx.ipr.impl;
 
 #ifndef IPR_STD_PREAMBLE_INCLUDED
 #define IPR_STD_PREAMBLE_INCLUDED