feat: number each build of a dev tree

The version alone cannot tell one build of an unreleased X.Y.Z from
another, and the user rebuilds and hand-tests unreleased builds daily.
They chose a counter over a git description: what they want to know is
that the binary is newer than the one they were running, not which
commit it came from.

QTMAILDIR_BUILD_NUMBER is a cmake option, ON by default, that runs
cmake/BuildNumber.cmake as a build step to increment a counter and write
buildnumber.h. It had to be a build step: configure_file runs once per
cmake run, so a counter interpolated into version.h.in would sit still
across exactly the rebuilds this exists to distinguish, which is why
version.h.in includes a second generated header rather than carrying the
number itself.

Two macros, and the split is load-bearing. QTMAILDIR_VERSION stays a
clean X.Y.Z and keeps the window title, applicationVersion and anything
that might ever compare versions; QTMAILDIR_VERSION_DISPLAY carries the
number and goes to the three surfaces the user picked, --version and
--help, the About dialog, and the placeholder pane. The window title was
offered and declined, since the number would then be in every
screenshot.

The counter lives in the build directory and is not tracked, so it
cannot conflict on a pull or leave the tree dirty; a fresh build
directory restarts at 1, which is honest, because it is a different
build tree. A release passes -DQTMAILDIR_BUILD_NUMBER=OFF and the header
is written empty. The SlackBuild in the my-slackbuilds repo needs that
flag and is a separate commit there.

Verified by running it, since none of this is reachable from a C++ test:
three consecutive builds reported build 2, 3 and 4, and a separate
Release configure with the option OFF reported a clean 0.27.0. Passing
the flag to a tree that does not have the option yet is an unused-cli
warning and exit 0, so the SlackBuild change is safe before 0.28.0
ships. The suite is 37 of 38, the one failure being item 136 on an
unrelated path.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HFuRPtzFrSxCQjFk6tq7gD

1 files changed, 39 insertions, 0 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9b4426c..e3cf82b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,12 @@ set(CMAKE_AUTORCC ON)
 # that ships.
 option(QTMAILDIR_BUILD_TESTS "Build the test suite" ON)
 
+# A dev build counts its own rebuilds so one binary of an unreleased X.Y.Z can
+# be told from another (item 167). OFF for a release: the version a release
+# prints must be a clean X.Y.Z, which the release procedure checks and the
+# SlackBuild builds from a tarball that carries no counter at all.
+option(QTMAILDIR_BUILD_NUMBER "Number each build of a dev tree" ON)
+
 set(QTMAILDIR_QT_COMPONENTS Widgets Svg WebEngineWidgets)
 if(QTMAILDIR_BUILD_TESTS)
     list(APPEND QTMAILDIR_QT_COMPONENTS Test)
@@ -58,6 +64,39 @@ configure_file(
     ${CMAKE_CURRENT_BINARY_DIR}/generated/qtmaildir/version.h
     @ONLY)
 
+# buildnumber.h is generated separately, and by a BUILD step rather than by
+# configure_file: this whole block runs once per cmake run, so a counter
+# written here would not move when the user rebuilt after a fix, which is the
+# defect item 167 describes. The header always exists so version.h can include
+# it unconditionally; in a release build it is empty and
+# QTMAILDIR_VERSION_DISPLAY collapses to the plain version.
+set(QTMAILDIR_BUILD_NUMBER_HEADER
+    ${CMAKE_CURRENT_BINARY_DIR}/generated/qtmaildir/buildnumber.h)
+
+if(QTMAILDIR_BUILD_NUMBER)
+    # Once now, so the header exists before the first compile of a fresh build
+    # directory, and then again on every build.
+    execute_process(COMMAND ${CMAKE_COMMAND}
+        -DCOUNTER_FILE=${CMAKE_CURRENT_BINARY_DIR}/build-number
+        -DHEADER_FILE=${QTMAILDIR_BUILD_NUMBER_HEADER}
+        -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/BuildNumber.cmake)
+
+    add_custom_target(qtmaildir_buildnumber ALL
+        COMMAND ${CMAKE_COMMAND}
+            -DCOUNTER_FILE=${CMAKE_CURRENT_BINARY_DIR}/build-number
+            -DHEADER_FILE=${QTMAILDIR_BUILD_NUMBER_HEADER}
+            -P ${CMAKE_CURRENT_SOURCE_DIR}/cmake/BuildNumber.cmake
+        BYPRODUCTS ${QTMAILDIR_BUILD_NUMBER_HEADER}
+        COMMENT "Numbering this build"
+        VERBATIM)
+else()
+    file(WRITE ${QTMAILDIR_BUILD_NUMBER_HEADER}
+        "// Release build: no counter, so QTMAILDIR_VERSION_DISPLAY is the
+// plain version. Generated by the top-level CMakeLists.txt.
+#pragma once
+")
+endif()
+
 add_subdirectory(src)
 if(QTMAILDIR_BUILD_TESTS)
     enable_testing()