1 files changed, 38 insertions, 0 deletions
diff --git a/cmake/BuildNumber.cmake b/cmake/BuildNumber.cmake
new file mode 100644
index 0000000..a79f1e7
--- /dev/null
+++ b/cmake/BuildNumber.cmake
@@ -0,0 +1,38 @@
+# Increment the build counter and write buildnumber.h.
+#
+# Run with `cmake -P` as a build step, so it fires on every build rather than
+# once per configure. Item 167: the version alone cannot tell one build of an
+# unreleased X.Y.Z from another, and the user hand-tests unreleased builds
+# daily.
+#
+# Expects COUNTER_FILE and HEADER_FILE on the command line.
+#
+# The counter lives in the BUILD directory and is deliberately not tracked: a
+# committed counter would conflict on every pull and leave the tree dirty
+# after every build. A fresh build directory therefore restarts at 1, which is
+# honest, since it is a different build tree.
+
+if(EXISTS "${COUNTER_FILE}")
+    file(READ "${COUNTER_FILE}" current)
+    string(STRIP "${current}" current)
+endif()
+
+if(NOT current MATCHES "^[0-9]+$")
+    set(current 0)
+endif()
+
+math(EXPR next "${current} + 1")
+file(WRITE "${COUNTER_FILE}" "${next}\n")
+
+# Written to a temporary and copied only if different, so a rebuild that
+# changes nothing else does not force every translation unit including
+# version.h to recompile... except that the number itself changes every time,
+# so it always differs. That is the accepted cost of the feature: the few
+# files that read the version are recompiled and relinked on every build.
+file(WRITE "${HEADER_FILE}.tmp"
+"// Generated by cmake/BuildNumber.cmake on every build. Do not edit, and do
+// not commit: this file lives in the build directory.
+#pragma once
+#define QTMAILDIR_BUILD_NUMBER \"${next}\"
+")
+file(COPY_FILE "${HEADER_FILE}.tmp" "${HEADER_FILE}" ONLY_IF_DIFFERENT)