common.pri: fix create empty error in windows

common.pri

@@ -130,6 +130,18 @@ defineReplace(qtLongName) {
 	return($$LONG_NAME)
 }
 
+defineTest(empty_file) {
+    isEmpty(1): error("empty_file(name) requires one argument")
+#"type NUL >filename" can create an empty file in windows, see http://stackoverflow.com/questions/210201/how-to-create-empty-text-file-from-a-batch-file
+# 'echo. >file' or 'echo >file' will insert a new line, so use stderr
+    win32:isEmpty(QMAKE_SH) {
+        system("echo. 2> $$1")|return(false)
+    } else {
+#if sh is after win's echo, then "echo >$$1" fails because win's echo is used
+        system("sh -c echo 2> $$1")|return(false)
+    }
+}
+
 lessThan(QT_MAJOR_VERSION, 5): {
 
 defineTest(write_file) {
@@ -140,21 +152,17 @@ defineTest(write_file) {
 ## echo a string with "\n" will fail, so we can not use join
     #val = $$join($$2, $$escape_expand(\n))$$escape_expand(\n)
     isEmpty(3)|!isEqual(3, append) {
-        #win32:system("echo. > $$1")|return(false) #may has sh
-        #else
-        system("$$QMAKE_DEL_FILE $$1")
+#system("$$QMAKE_DEL_FILE $$1") #for win commad "del", path format used in qmake such as D:/myfile is not supported, "/" will be treated as an otpion for "del"
+        empty_file($$1)
     }
     for(val, $$2) {
-        system("echo $$val >> $$1")|return(false)
+        system("echo $$val >> \"$$1\"")|return(false)
     }
     return(true)
 }
 
 #defineTest(cache) {
 #    !isEmpty(4): error("cache(var, [set|add|sub] [transient] [super], [srcvar]) requires one to three arguments.")
-
-#}
-
 #}
 
 }
@@ -165,8 +173,9 @@ defineTest(getBuildRoot) {
     isEmpty(BUILD_DIR) {
         BUILD_DIR=$$(BUILD_DIR)
         isEmpty(BUILD_DIR) {
-            exists($$PROJECTROOT/.build.cache):include($$PROJECTROOT/.build.cache)
-message("BUILD_DIR=$$BUILD_DIR")
+            build_cache = $$PROJECTROOT/.build.cache #use root project's cache for subdir projects
+            !exists($$build_cache):build_cache = $$PWD/.build.cache #common.pri is in the root dir of a sub project
+            exists($$build_cache):include($$build_cache)
             isEmpty(BUILD_DIR) {
                 BUILD_DIR=$$[BUILD_DIR]
                 isEmpty(BUILD_DIR) {
@@ -215,7 +224,7 @@ defineTest(preparePaths) {
     export(UI_DIR)
     export(OBJECTS_DIR)
     export(DESTDIR)
-    export(TARGET)
+    #export(TARGET)
     return(true)
 }
 COMMON_PRI_INCLUDED = 1