tweak: filter redundant flags in flag attrs (#3849)

* tweak: filter redundant flags in flag attrs

This trick gets rid of unneeded flags in flag attrs that even
contextually don't make sense.
Most commonly: android:layout_gravity="bottom|center|left"

000000000000000000000011 (left)
000000000000000000010001 (center)
000000000000000001010000 (bottom)

'left|bottom' already covers the bits set by 'center',
and contextually something can't be left, bottom and center
all at once. There are very few flag attrs like that, where
certain flags overlap, but this fixes this annoyance when
editing res XMLs.

* micro-optimize

* optimize: redundancy only possible with flags > 2

Author: IgorEisberg

brut.apktool/apktool-lib/src/main/java/brut/androlib/res/data/value/ResAttr.java

@@ -135,34 +135,34 @@ protected void serializeBody(XmlSerializer serializer, ResResource res)
     }
 
     protected String getTypeAsString() {
-        String s = "";
+        StringBuilder sb = new StringBuilder();
         if ((mType & TYPE_REFERENCE) != 0) {
-            s += "|reference";
+            sb.append("|reference");
         }
         if ((mType & TYPE_STRING) != 0) {
-            s += "|string";
+            sb.append("|string");
         }
         if ((mType & TYPE_INT) != 0) {
-            s += "|integer";
+            sb.append("|integer");
         }
         if ((mType & TYPE_BOOL) != 0) {
-            s += "|boolean";
+            sb.append("|boolean");
         }
         if ((mType & TYPE_COLOR) != 0) {
-            s += "|color";
+            sb.append("|color");
         }
         if ((mType & TYPE_FLOAT) != 0) {
-            s += "|float";
+            sb.append("|float");
         }
         if ((mType & TYPE_DIMEN) != 0) {
-            s += "|dimension";
+            sb.append("|dimension");
         }
         if ((mType & TYPE_FRACTION) != 0) {
-            s += "|fraction";
+            sb.append("|fraction");
         }
-        if (s.isEmpty()) {
+        if (sb.length() == 0) {
             return null;
         }
-        return s.substring(1);
+        return sb.substring(1);
     }
 }

brut.apktool/apktool-lib/src/main/java/brut/androlib/res/data/value/ResFlagsAttr.java

@@ -55,28 +55,70 @@ public String convertToResXmlFormat(ResScalarValue value) throws AndrolibExcepti
             return super.convertToResXmlFormat(value);
         }
         loadFlags();
-        int intVal = ((ResIntValue) value).getValue();
 
+        int intVal = ((ResIntValue) value).getValue();
         if (intVal == 0) {
             return renderFlags(mZeroFlags);
         }
 
-        FlagItem[] flagItems = new FlagItem[mFlags.length];
-        int[] flags = new int[mFlags.length];
+        FlagItem[] flags = new FlagItem[mFlags.length];
         int flagsCount = 0;
-        for (FlagItem flagItem : mFlags) {
-            int flag = flagItem.flag;
+        int flagsInt = 0;
+
+        for (FlagItem item : mFlags) {
+            int flag = item.flag;
 
-            if ((intVal & flag) != flag) {
+            if ((intVal & flag) != flag || (flagsInt & flag) == flag) {
                 continue;
             }
 
-            if (!isSubpartOf(flag, flags)) {
-                flags[flagsCount] = flag;
-                flagItems[flagsCount++] = flagItem;
+            flags[flagsCount++] = item;
+            flagsInt |= flag;
+
+            if (intVal == flagsInt) {
+                break;
             }
         }
-        return renderFlags(Arrays.copyOf(flagItems, flagsCount));
+
+        if (flagsCount == 0) {
+            throw new AndrolibException(String.format("invalid flags in value: 0x%08x", intVal));
+        }
+
+        // Filter out redundant flags
+        if (flagsCount > 2) {
+            FlagItem[] filtered = new FlagItem[flagsCount];
+            int filteredCount = 0;
+
+            for (int i = 0; i < flagsCount; i++) {
+                FlagItem item = flags[i];
+                int mask = 0;
+
+                // Combine the other flags
+                for (int j = 0; j < flagsCount; j++) {
+                    FlagItem other = flags[j];
+
+                    if (j != i && other != null) {
+                        mask |= other.flag;
+                    }
+                }
+
+                // Keep only if it adds at least one unique bit
+                if ((item.flag & ~mask) != 0) {
+                    filtered[filteredCount++] = item;
+                } else {
+                    flags[i] = null;
+                }
+            }
+
+            flags = filtered;
+            flagsCount = filteredCount;
+        }
+
+        if (flagsCount != flags.length) {
+            flags = Arrays.copyOf(flags, flagsCount);
+        }
+
+        return renderFlags(flags);
     }
 
     @Override
@@ -98,15 +140,6 @@ protected void serializeBody(XmlSerializer serializer, ResResource res)
         }
     }
 
-    private boolean isSubpartOf(int flag, int[] flags) {
-        for (int f : flags) {
-            if ((f & flag) == flag) {
-                return true;
-            }
-        }
-        return false;
-    }
-
     private String renderFlags(FlagItem[] flags) throws AndrolibException {
         StringBuilder sb = new StringBuilder();
         for (FlagItem flag : flags) {
@@ -139,6 +172,8 @@ private void loadFlags() {
         mZeroFlags = Arrays.copyOf(zeroFlags, zeroFlagsCount);
         mFlags = Arrays.copyOf(flags, flagsCount);
 
-        Arrays.sort(mFlags, Comparator.comparingInt((FlagItem item) -> Integer.bitCount(item.flag)).reversed());
+        Arrays.sort(mFlags,
+            Comparator.comparingInt((FlagItem item) -> Integer.bitCount(item.flag)).reversed()
+            .thenComparingInt((FlagItem item) -> item.flag));
     }
 }

brut.apktool/apktool-lib/src/test/java/brut/androlib/aapt2/NetworkConfigTest.java

@@ -65,12 +65,12 @@ public void netSecConfGeneric() throws BrutException {
         Document doc = loadDocument(new File(sTestNewDir, "res/xml/network_security_config.xml"));
 
         // Check if 'system' certificate exists
-        String systemCertExpr = "//base-config//certificates[@src='system']";
+        String systemCertExpr = "/network-security-config/base-config/trust-anchors/certificates[@src='system']";
         NodeList systemCertNodes = evaluateXPath(doc, systemCertExpr, NodeList.class);
         assertTrue(systemCertNodes.getLength() > 0);
 
         // Check if 'user' certificate exists
-        String userCertExpr = "//base-config//certificates[@src='user']";
+        String userCertExpr = "/network-security-config/base-config/trust-anchors/certificates[@src='user']";
         NodeList userCertNodes = evaluateXPath(doc, userCertExpr, NodeList.class);
         assertTrue(userCertNodes.getLength() > 0);
     }