ext(sqlcipher): add check to extconf for sqlcipher

and add test coverage to make sure the compiled and loaded versions
are the same.

ext/sqlite3/extconf.rb

@@ -39,12 +39,12 @@ def sqlcipher?
         with_config("sqlcipher") ||
           with_config("sqlcipher-dir") ||
           with_config("sqlcipher-include") ||
-          with_config("sqlcipher-lib")
+          with_config("sqlcipher-lib") ||
+          false
       end
 
       def configure_system_libraries
         pkg_config(libname)
-        append_cflags("-DUSING_SQLCIPHER") if sqlcipher?
       end
 
       def configure_packaged_libraries
@@ -81,6 +81,14 @@ def configure_extension
         abort_could_not_find("sqlite3.h") unless find_header("sqlite3.h")
         abort_could_not_find(libname) unless find_library(libname, "sqlite3_libversion_number", "sqlite3.h")
 
+        # double-check that we're using the expected library (sqlite3 or sqlcipher)
+        #
+        # note that sqlcipher doesn't provide a C function for its version :(
+        # https://github.com/sqlcipher/sqlcipher/issues/354
+        actually_sqlcipher = have_func("sqlcipher_activate")
+        abort("\nWanted #{libname} but sqlcipher is #{actually_sqlcipher}\n\n") if actually_sqlcipher != sqlcipher?
+        append_cflags("-DUSING_SQLCIPHER") if sqlcipher?
+
         # Functions defined in 1.9 but not 1.8
         have_func('rb_proc_arity')
 

test/test_sqlite3.rb

@@ -22,5 +22,9 @@ def test_version_strings
       skip if SQLite3::VERSION.include?("test") # see set-version-to-timestamp rake task
       assert_equal(SQLite3::VERSION, SQLite3::VersionProxy::STRING)
     end
+
+    def test_compiled_version_and_loaded_version
+      assert_equal(SQLite3::SQLITE_VERSION, SQLite3::SQLITE_LOADED_VERSION)
+    end
   end
 end