Add checker for static final buffers

common/src/main/java/io/netty/build/checkstyle/StaticFinalBufferCheck.java

@@ -0,0 +1,53 @@
+package io.netty.build.checkstyle;
+
+import com.puppycrawl.tools.checkstyle.api.*;
+
+import java.util.regex.Pattern;
+
+public class StaticFinalBufferCheck extends AbstractCheck {
+
+    private static final Pattern pattern = Pattern.compile(
+            "(Unpooled\\s*\\.)?unreleasableBuffer\\(.*?\\)\\s*\\.asReadOnly\\(\\)",
+            Pattern.MULTILINE);
+
+    @Override
+    public int[] getRequiredTokens() {
+        return new int[]{TokenTypes.VARIABLE_DEF};
+    }
+
+    @Override
+    public int[] getDefaultTokens() {
+        return this.getRequiredTokens();
+    }
+
+    @Override
+    public int[] getAcceptableTokens() {
+        return this.getRequiredTokens();
+    }
+
+    @Override
+    public void visitToken(DetailAST ast) {
+        DetailAST modifiersAST = ast.findFirstToken(TokenTypes.MODIFIERS);
+        boolean isStatic = modifiersAST.findFirstToken(TokenTypes.LITERAL_STATIC) != null;
+        boolean isFinal = modifiersAST.findFirstToken(TokenTypes.FINAL) != null;
+        FullIdent typeIdent = FullIdent.createFullIdentBelow(ast.findFirstToken(TokenTypes.TYPE));
+        if (!isStatic || !isFinal || !typeIdent.getText().endsWith("Buf")) {
+            return;
+        }
+        DetailAST assignAST = ast.findFirstToken(TokenTypes.ASSIGN);
+        DetailAST semiAST = ast.findFirstToken(TokenTypes.SEMI);
+        if (assignAST == null || semiAST == null) {
+            log(ast.getLineNo(), "Missing assignment for static final buffer");
+            return;
+        }
+        FileContents fc = getFileContents();
+        StringBuilder sb = new StringBuilder();
+        for (int i = assignAST.getLineNo(); i <= semiAST.getLineNo(); i++) {
+            // getLineNo returns 1-based line number, getLine expects 0-based.
+            sb.append(fc.getLine(i - 1));
+        }
+        if (!pattern.matcher(sb.toString()).find()) {
+            log(ast.getLineNo(), "static final buffer assignment should match pattern " + pattern);
+        }
+    }
+}

common/src/main/resources/io/netty/checkstyle.xml

@@ -55,7 +55,7 @@
   <module name="RegexpSingleline">
     <property name="format" value="\s+$"/>
     <property name="message" value="trailing whitespace"/>
-  </module> 
+  </module>
   <!-- Prohibit consecutive empty lines (except the lines after package/import) -->
   <module name="RegexpMultiline">
     <property name="format" value="\n *(?!package )(?!import )[^\n]+\n{3,}"/>
@@ -77,6 +77,8 @@
   </module>
 
   <module name="TreeWalker">
+    <!-- Make sure final static buffers are unreleasable and read-only. -->
+    <module name="io.netty.build.checkstyle.StaticFinalBufferCheck"/>
     <module name="WhitespaceAfter"/>
     <module name="WhitespaceAround">
       <property name="tokens" value="ASSIGN, BAND, BAND_ASSIGN, BOR, BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR, BXOR_ASSIGN, DIV, DIV_ASSIGN, EQUAL, GE, GT, LAND, LCURLY, LE, LITERAL_ASSERT, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF, LITERAL_RETURN, LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS, MINUS_ASSIGN, MOD, MOD_ASSIGN, NOT_EQUAL, PLUS, PLUS_ASSIGN, RCURLY, SL, SLIST, SL_ASSIGN, SR, SR_ASSIGN, STAR, STAR_ASSIGN, TYPE_EXTENSION_AND"/>