Update to put the tag into the binaries

utils/build_date.h

@@ -10,7 +10,8 @@
 #include <ctime>
 #include <sys/stat.h>
 
-/// git commit this binary was built from, with a "-dirty" marker when the tree
+/// git commit this binary was built from, described relative to the latest
+/// release tag (e.g. v1.10.0-12-gc719a4ac), with a "-dirty" marker when the tree
 /// carried uncommitted changes. Defined in provenance.cpp, which is the only
 /// translation unit that includes the generated version.h, so that a change of
 /// hash recompiles one file instead of everything including this header.

utils/gen_version.cmake

@@ -11,7 +11,16 @@
 #          leave OUT_FILE alone when nothing changed, avoiding a rebuild.
 # ----------------------------------------------------------------------------
 
-execute_process( COMMAND git rev-parse --short HEAD
+# Name the build relative to the most recent release tag, e.g.
+# v1.10.0-12-gc719a4ac is 12 commits past v1.10.0 at commit c719a4ac.
+#
+# --long keeps the hash even on a tagged commit (v1.10.0-0-g...), because a
+# tag can be moved or deleted but the hash always names the commit.
+# --match restricts this to annotated release tags of the form vX.Y.Z.
+# --always falls back to the bare hash when no tag is reachable, such as in
+# a shallow clone.
+#
+execute_process( COMMAND git describe --long --always --match "v[0-9]*"
                  WORKING_DIRECTORY ${SRC_DIR}
                  OUTPUT_VARIABLE GIT_COMMIT_HASH
                  OUTPUT_STRIP_TRAILING_WHITESPACE

utils/version.h.in

@@ -11,4 +11,6 @@
  */
 #pragma once
 
-#define GIT_COMMIT_HASH "@GIT_COMMIT_HASH@"  ///< hash, hash-dirty, or "unknown"
+/// git describe output, e.g. v1.10.0-12-gc719a4ac[-dirty]; a bare hash if no
+/// release tag is reachable; or "unknown" if git is unavailable
+#define GIT_COMMIT_HASH "@GIT_COMMIT_HASH@"