version.cmake: switch SOF_MAJOR etc. to a new, static versions.json

As discussed in #6952, relying on `git describe` for defining SOF_MAJOR
and friends is very brittle and unreliable. Switch to a static
versions.json file instead.

Note the full `git describe --tags` output is _still_ present in the
binary, this is useful and left unchanged. It's just not used any more
to guess SOF_MAJOR, SOF_MINOR and SOF_MICRO.

Use JSON because CMake and pretty much every other piece of software has
a JSON parser out of the box.

This aligns with linux/Makefile, Zephyr/VERSIONS and probably many
others. - except we use JSON because we're in 2023 so we don't spend
time having fun re-implementing parsers any more.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

Author: marc-hb

scripts/cmake/version.cmake

@@ -1,13 +1,13 @@
 # SPDX-License-Identifier: BSD-3-Clause
 
 # Generates header for which version is taken from (in order of precedence):
-# 	1) .tarball-version file
-#	2) git
+#	1) .tarball-version file
+#	2) sof/versions.json
 #
 # Version is checked during configuration step and for every target
 # that has check_version_h target as dependency
 
-cmake_minimum_required(VERSION 3.13)
+cmake_minimum_required(VERSION 3.19)
 
 set(VERSION_CMAKE_PATH ${CMAKE_CURRENT_LIST_DIR}/version.cmake)
 
@@ -74,12 +74,19 @@ endif()
 
 message(STATUS "GIT_TAG / GIT_LOG_HASH : ${GIT_TAG} / ${GIT_LOG_HASH}")
 
-string(REGEX MATCH "^v([0-9]+)[.]([0-9]+)([.]([0-9]+))?" ignored "${GIT_TAG}")
-set(SOF_MAJOR ${CMAKE_MATCH_1})
-set(SOF_MINOR ${CMAKE_MATCH_2})
-set(SOF_MICRO ${CMAKE_MATCH_4})
+file(READ "${SOF_ROOT_SOURCE_DIRECTORY}/versions.json" versions_json)
 
-if(NOT SOF_MICRO MATCHES "^[0-9]+$")
+message(VERBOSE "${SOF_ROOT_SOURCE_DIRECTORY}/versions.json=${versions_json}")
+
+string(JSON SOF_MAJOR GET "${versions_json}" SOF MAJOR)
+string(JSON SOF_MINOR GET "${versions_json}" SOF MINOR)
+string(JSON SOF_MICRO ERROR_VARIABLE micro_error
+                      GET "${versions_json}" SOF MICRO)
+
+# Don't confuse "error not found" with "version not found"
+if(NOT "${micro_error}" STREQUAL "NOTFOUND")
+	message(STATUS "versions.json: ${micro_error}, defaulting to 0")
+	# TODO: default this to .99 on the main, never released branch like zephyr does
 	set(SOF_MICRO 0)
 endif()
 

versions.json

@@ -0,0 +1,6 @@
+{
+  "SOF": {
+    "MAJOR": "2",
+    "MINOR": "5"
+  }
+}