fixes bug 311456 "Calling Truncate() on an nsAutoString makes next append work hard and doesn't clear F_VOIDED flag" r=bzbarsky

xpcom/string/src/nsTSubstring.cpp

@@ -79,8 +79,10 @@ nsTSubstring_CharT::MutatePrep( size_type capacity, char_type** oldData, PRUint3
 
     if (curCapacity != size_type(-1))
       {
-        if (capacity <= curCapacity)
+        if (capacity <= curCapacity) {
+          mFlags &= ~F_VOIDED;  // mutation clears voided flag
           return PR_TRUE;
+        }
 
         if (curCapacity > 0)
           {
@@ -119,6 +121,7 @@ nsTSubstring_CharT::MutatePrep( size_type capacity, char_type** oldData, PRUint3
 
             hdr = newHdr;
             mData = (char_type*) hdr->Data();
+            mFlags &= ~F_VOIDED;  // mutation clears voided flag
             return PR_TRUE;
           }
       }
@@ -562,6 +565,11 @@ nsTSubstring_CharT::SetCapacity( size_type capacity )
 void
 nsTSubstring_CharT::SetLength( size_type length )
   {
+    if (mLength == length) {
+      mFlags &= ~F_VOIDED;  // mutation clears voided flag
+      return;
+    }
+
     SetCapacity(length);
 
     // XXX(darin): SetCapacity may fail, but it doesn't give us a way to find

xpcom/tests/TestStrings.cpp

@@ -613,6 +613,68 @@ PRBool test_stringbuffer()
     return rv;
   }
 
+PRBool test_voided()
+  {
+    const char kData[] = "hello world";
+
+    nsXPIDLCString str;
+    if (str)
+      return PR_FALSE;
+    if (!str.IsVoid())
+      return PR_FALSE;
+    if (!str.IsEmpty())
+      return PR_FALSE;
+
+    str.Assign(kData);
+    if (strcmp(str, kData) != 0)
+      return PR_FALSE;
+
+    str.SetIsVoid(PR_TRUE);
+    if (str)
+      return PR_FALSE;
+    if (!str.IsVoid())
+      return PR_FALSE;
+    if (!str.IsEmpty())
+      return PR_FALSE;
+
+    str.SetIsVoid(PR_FALSE);
+    if (strcmp(str, "") != 0)
+      return PR_FALSE;
+
+    return PR_TRUE;
+  }
+
+PRBool test_voided_autostr()
+  {
+    const char kData[] = "hello world";
+
+    nsCAutoString str;
+    if (str.IsVoid())
+      return PR_FALSE;
+    if (!str.IsEmpty())
+      return PR_FALSE;
+
+    str.Assign(kData);
+    if (strcmp(str.get(), kData) != 0)
+      return PR_FALSE;
+
+    str.SetIsVoid(PR_TRUE);
+    if (!str.IsVoid())
+      return PR_FALSE;
+    if (!str.IsEmpty())
+      return PR_FALSE;
+
+    str.Assign(kData);
+    if (str.IsVoid())
+      return PR_FALSE;
+    if (str.IsEmpty())
+      return PR_FALSE;
+    if (strcmp(str.get(), kData) != 0)
+      return PR_FALSE;
+
+    return PR_TRUE;
+  }
+
 //----
 
 typedef PRBool (*TestFunc)();
@@ -651,6 +713,8 @@ tests[] =
     { "test_findcharinset", test_findcharinset },
     { "test_rfindcharinset", test_rfindcharinset },
     { "test_stringbuffer", test_stringbuffer },
+    { "test_voided", test_voided },
+    { "test_voided_autostr", test_voided_autostr },
     { nsnull, nsnull }
   };