configure.ac, src/Makefile.am, add libtool versioning for shared library

configure.ac

@@ -14,6 +14,17 @@
 # Initialisation of configure
 AC_INIT([ngspice], [26], [http://ngspice.sourceforge.net/bugrep.html])
 
+# libtool versioning for shared libraries current:revision:age
+# current The most recent interface number that this library implements.
+# revision The implementation number of the current interface.
+# age The difference between the newest and oldest interfaces that this library implements.
+# In other words, the library implements all the interface numbers in the
+# range from numbers (current - age) to current.
+# libtool in msys2 generates a single version number (current-age)
+# libtool in LINUX generates the numbers as: (current-age).age.revision
+# LIBRARY_VERSION may be overridden by external LIB_VERSION
+LIBRARY_VERSION="0:0:0"
+
 # Unique file in the source directory
 AC_CONFIG_SRCDIR([src/ngspice.c])
 
@@ -300,6 +311,12 @@ else
     dprefix=$prefix
 fi
 
+# external LIB_VERSION ?
+ext_LIB_VERSION=${LIB_VERSION+yes}
+if test "x$ext_LIB_VERSION" != xyes; then
+    LIB_VERSION=$LIBRARY_VERSION
+fi
+
 ##########################################################################
 #
 # ngspice as shared library (ngspice.so or ngspice.dll)
@@ -482,6 +499,7 @@ else
     TCL_PACKAGE_PATH=""
     TCL_LIB_SPEC=""
     AC_SUBST([STATIC], [-static])
+    LIB_VERSION=""
 fi
 
 
@@ -494,6 +512,7 @@ AM_CONDITIONAL([TCLCYG], [test "x$has_tclcyg" = xtrue])
 
 AC_SUBST([TCL_PACKAGE_PATH])
 AC_SUBST([TCL_LIB_SPEC])
+AC_SUBST([LIB_VERSION])
 ##################################################################
 #
 #

src/Makefile.am

@@ -541,7 +541,7 @@ libngspice_la_LIBADD += \
 
 libngspice_la_CFLAGS = -shared
 
-libngspice_la_LDFLAGS =  -shared
+libngspice_la_LDFLAGS =  -shared -version-info @LIB_VERSION@
 
 if SHWIN
 libngspice_la_LDFLAGS += -Wl,--output-def=ngspice.def  -Wl,--out-implib=ngspice.dll.a