Generate build information from CHANGES.md

This PR significantly reworks the way glslang is versioned.

Instead of committing changes to the `GLSLANG_MINOR_VERSION` define in
`glslang/Public/ShaderLang.h`, and using `make-revision` to generate
`GLSLANG_PATCH_LEVEL` in `glslang/Include/revision.h`, all version
information is now derived from the new `CHANGES.md` file.

`CHANGES.md` acts as the single source of truth for glslang version
information, along with a convenient place to put all release notes for
each notable change made.

`CHANGES.md` is parsed using the new `build_info.py` python script.
This script can read basic template files to produce new source files,
which it does to read the new `build_info.h.tmpl` to generate (at build
time) a glslang private header at
`<build-dir>/include/glslang/build_info.h`.
I've written generators for each of the CMake, Bazel, gn, and
`Android.mk` build scripts.

The new version code conforms to the Semantic Versioning 2.0 spec.

This new version is also used by the CMake rules to produce versioned
shared objects, including a major-versioned SONAME.

New APIs:
---------

* `glslang::GetVersion()` returns a `Version` struct with the version
  major, minor, patch and flavor.

Breaking API changes:
---------------------

* The public defines `GLSLANG_MINOR_VERSION` and `GLSLANG_PATCH_LEVEL`
  have been entirely removed.
* `glslang/Public/ShaderLang.h` and `glslang/Include/revision.h` have
  been deleted.
* Instead, `<build-dir>/include/glslang/build_info.h` is created in
  the build directory, and `<build-dir>/include` is a CMake `PUBLIC`
  (dependee-inherited) include directory for the glslang targets.
* `<build-dir>/include/glslang/build_info.h` contains the following
   new #defines:
   `GLSLANG_VERSION_MAJOR`, `GLSLANG_VERSION_MINOR`,
   `GLSLANG_VERSION_PATCH`, `GLSLANG_VERSION_FLAVOR`,
   `GLSLANG_VERSION_GREATER_THAN(major, minor, patch)`,
   `GLSLANG_VERSION_GREATER_OR_EQUAL_TO(major, minor, patch)`,
   `GLSLANG_VERSION_LESS_THAN(major, minor, patch)`,
   `GLSLANG_VERSION_LESS_OR_EQUAL_TO(major, minor, patch)`
*  The CMake install output directory contains a copy of
   `build_info.h` at: `include/glslang/build_info.h`
*  Python3 is now always required to build glslang (likely always
   required for transitive dependency builds).

glslang/CMakeLists.txt

@@ -133,6 +133,9 @@ endif(ENABLE_HLSL)
 add_library(MachineIndependent STATIC ${MACHINEINDEPENDENT_SOURCES} ${MACHINEINDEPENDENT_HEADERS})
 set_property(TARGET MachineIndependent PROPERTY POSITION_INDEPENDENT_CODE ON)
 set_property(TARGET MachineIndependent PROPERTY FOLDER glslang)
+
+glslang_add_build_info_dependency(MachineIndependent)
+
 glslang_pch(MachineIndependent MachineIndependent/pch.h)
 
 target_link_libraries(MachineIndependent PRIVATE OGLCompiler OSDependent GenericCodeGen)
@@ -156,18 +159,22 @@ set(GLSLANG_HEADERS
     Include/intermediate.h
     Include/PoolAlloc.h
     Include/ResourceLimits.h
-    Include/revision.h
     Include/ShHandle.h
     Include/Types.h)
 
 add_library(glslang ${LIB_TYPE} ${BISON_GLSLParser_OUTPUT_SOURCE} ${GLSLANG_SOURCES} ${GLSLANG_HEADERS})
-set_property(TARGET glslang PROPERTY FOLDER glslang)
-set_property(TARGET glslang PROPERTY POSITION_INDEPENDENT_CODE ON)
+set_target_properties(glslang PROPERTIES
+    FOLDER glslang
+    POSITION_INDEPENDENT_CODE ON
+    VERSION   "${GLSLANG_VERSION}"
+    SOVERSION "${GLSLANG_VERSION_MAJOR}")
 target_link_libraries(glslang PRIVATE OGLCompiler OSDependent MachineIndependent)
 target_include_directories(glslang PUBLIC
     $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
     $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>)
 
+glslang_add_build_info_dependency(glslang)
+
 glslang_only_export_explicit_symbols(glslang)
 
 if(WIN32 AND BUILD_SHARED_LIBS)
@@ -213,4 +220,7 @@ if(ENABLE_GLSLANG_INSTALL)
         get_filename_component(dir ${file} DIRECTORY)
         install(FILES ${file} DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/glslang/${dir})
     endforeach()
+
+    install(FILES ${GLSLANG_BUILD_INFO_H} DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/glslang)
+
 endif(ENABLE_GLSLANG_INSTALL)

glslang/Include/revision.h

@@ -1,3 +0,0 @@
-// This header is generated by the make-revision script.
-
-#define GLSLANG_PATCH_LEVEL 3847

glslang/Include/revision.template

@@ -1,13 +0,0 @@
-// The file revision.h should be updated to the latest version, somehow, on
-// check-in, if glslang has changed.
-//
-// revision.template is the source for revision.h when using SubWCRev as the
-// method of updating revision.h.  You don't have to do it this way, the
-// requirement is only that revision.h gets updated.
-//
-// revision.h is under source control so that not all consumers of glslang
-// source have to figure out how to create revision.h just to get a build
-// going.  However, if it is not updated, it can be a version behind.
-
-#define GLSLANG_REVISION "$WCREV$"
-#define GLSLANG_DATE     "$WCDATE$"

glslang/MachineIndependent/ShaderLang.cpp

@@ -72,6 +72,9 @@
 // token to print ", but none of that seems appropriate for this file.
 #include "preprocessor/PpTokens.h"
 
+// Build-time generated includes
+#include "glslang/build_info.h"
+
 namespace { // anonymous namespace for file-local functions and symbols
 
 // Total number of successful initializers of glslang: a refcount
@@ -1684,19 +1687,29 @@ int ShGetUniformLocation(const ShHandle handle, const char* name)
 
 namespace glslang {
 
-#include "../Include/revision.h"
+Version GetVersion()
+{
+    Version version;
+    version.major = GLSLANG_VERSION_MAJOR;
+    version.minor = GLSLANG_VERSION_MINOR;
+    version.patch = GLSLANG_VERSION_PATCH;
+    version.flavor = GLSLANG_VERSION_FLAVOR;
+    return version;
+}
 
 #define QUOTE(s) #s
 #define STR(n) QUOTE(n)
 
 const char* GetEsslVersionString()
 {
-    return "OpenGL ES GLSL 3.20 glslang Khronos. " STR(GLSLANG_MINOR_VERSION) "." STR(GLSLANG_PATCH_LEVEL);
+    return "OpenGL ES GLSL 3.20 glslang Khronos. " STR(GLSLANG_VERSION_MAJOR) "." STR(GLSLANG_VERSION_MINOR) "." STR(
+        GLSLANG_VERSION_PATCH) GLSLANG_VERSION_FLAVOR;
 }
 
 const char* GetGlslVersionString()
 {
-    return "4.60 glslang Khronos. " STR(GLSLANG_MINOR_VERSION) "." STR(GLSLANG_PATCH_LEVEL);
+    return "4.60 glslang Khronos. " STR(GLSLANG_VERSION_MAJOR) "." STR(GLSLANG_VERSION_MINOR) "." STR(
+        GLSLANG_VERSION_PATCH) GLSLANG_VERSION_FLAVOR;
 }
 
 int GetKhronosToolId()

glslang/Public/ShaderLang.h

@@ -74,11 +74,6 @@
     extern "C" {
 #endif
 
-// This should always increase, as some paths to do not consume
-// a more major number.
-// It should increment by one when new functionality is added.
-#define GLSLANG_MINOR_VERSION 15
-
 //
 // Call before doing any other compiler/linker operations.
 //
@@ -399,6 +394,14 @@ class TInfoSink;
 
 namespace glslang {
 
+struct Version {
+    int major;
+    int minor;
+    int patch;
+    const char* flavor;
+};
+
+GLSLANG_EXPORT Version GetVersion();
 GLSLANG_EXPORT const char* GetEsslVersionString();
 GLSLANG_EXPORT const char* GetGlslVersionString();
 GLSLANG_EXPORT int GetKhronosToolId();