ColorDetector - Lint detector

ColorDetector.java

public class ColorDetector extends ResourceXmlDetector {
  
  private static final String ID = "CustomColors";
  private static final String DESCRIPTION = "Custom colors used";
  private static final String EXPLANATION = "Use pre-defined (allowed) colors only";
  private static final Category CATEGORY = Category.CORRECTNESS;
  private static final int PRIORITY = 6;
  private static final Severity SEVERITY = Severity.ERROR;
  
  public static final Issue ISSUE = Issue.create(
    ID,
    DESCRIPTION,
    EXPLANATION,
    CATEGORY,
    PRIORITY,
    SEVERITY,
    new Implementation(ColorDetector.class, Scope.RESOURCE_FILE_SCOPE)
    );
  
  private Set<String> predefinedColors = new HashSet<>();
  private Set<String> allowedColors = new HashSet<>();
  private List<Pair<Attr, Location>> colorUsages = new ArrayList<>();
  
  @Override
  public Collection<String> getApplicableElements() {
    return Collections.singletonList("color");
  }
  
  @Override
  public Collection<String> getApplicableAttributes() {
    return Arrays.asList("color", "textColor", "background");
  }
  
  @Override
  public void beforeCheckProject(Context context) {
    // set-up the project
    allowedColors.clear();
    colorUsages.clear();
    // add predefined colors.
    // predefinedColors.add("my_awesome_color");
  }
  
  @Override
  public void visitElement(XmlContext context, Element element) {
    String value = null;
    NodeList nodes = element.getChildNodes();
    if (nodes.getLength() == 1) {
      // <color> element should have only one node
      Node node = nodes.item(0);
      // This gives us the color, eg. @color/my_awesome_color, #DDFFFF, etc
      value = node.getNodeValue();
    }
    
    if (value == null) {
      // Ideally, this should not happen.
      return;
    }
    
    if (value.startsWith("@color/")) {
      // check if the color name exists in predefined colors.
      if (predefinedColors.contains(value.substring(7))) {
        allowedColors.add(element.getAttribute("name"));
        return;
      }  
    }
          
    context.report(ISSUE, context.getLocation(element), "custom colors should refer to predefined colors");
  }
  
  @Override
  public void visitAttribute(XmlContext context, Attr attribute) {
    String content = attribute.getTextContent();
    if (content.startsWith("@color/")) {
      if (!predefinedColors.contains(content.substring(7))) {
        // the color is a custom color
        colorUsages.add(Pair.of(attribute, context.getLocation(attribute)));
      }
    } else if (content.startsWith("#")) {
      context.report(ISSUE, context.getLocation(attribute), "Do not use hardcoded colors");
    }
  }
  
  @Override
  public void afterCheckProject(Context context) {
    // filter and report
    for (Pair<Attr, Location> usage: colorUsages) {
      String content = usage.getFirst().getTextContent();
      if (content.startsWith("@color/")) {
        if (!allowedColors.contains(content.substring(7))) {
          context.report(ISSUE, usage.getSecond(), "custom color does not refer to predefined colors");
        }
      } else if (content.startsWith("#")) {
        context.report(ISSUE, usage.getSecond(), "Do not use hardcoded colors");
      }
    }
    
    // clean-up
    allowedColors.clear();
    colorUsages.clear();
    predefinedColors.clear();
  }
}

ColorDetectorWithEdgeCases.java

public class ColorDetector extends ResourceXmlDetector {
  
  private static final String ID = "CustomColors";
  private static final String DESCRIPTION = "Custom colors used";
  private static final String EXPLANATION = "Use pre-defined (allowed) colors only";
  private static final Category CATEGORY = Category.CORRECTNESS;
  private static final int PRIORITY = 6;
  private static final Severity SEVERITY = Severity.ERROR;
  
  public static final Issue ISSUE = Issue.create(
    ID,
    DESCRIPTION,
    EXPLANATION,
    CATEGORY,
    PRIORITY,
    SEVERITY,
    new Implementation(ColorDetector.class, Scope.RESOURCE_FILE_SCOPE)
    );
  
  private static final String TOOLS_SCHEMA = "http://schemas.android.com/tools";
  
  private Set<String> predefinedColors = new HashSet<>();
  private Set<String> allowedColors = new HashSet<>();
  // If the user has used tools:ingore, we don't want to raise issues for its usage.
  private Set<String> ignoredColors = new HashSet<>();
  private List<Pair<Attr, Location>> colorUsages = new ArrayList<>();
  
  // For res/color/ files.
  private int errorInAFile;
  
  @Override
  public Collection<String> getApplicableElements() {
    return Collections.singletonList("color");
  }
  
  @Override
  public Collection<String> getApplicableAttributes() {
    return Arrays.asList("color", "textColor", "background");
  }
  
  @Override
  public void beforeCheckProject(Context context) {
    // set-up the project
    allowedColors.clear();
    colorUsages.clear();
    // add predefined colors.
    // predefinedColors.add("my_awesome_color");
  }
  
  @Override
  public void beforeCheckFile(Context context) {
    errorsInAFile = 0;
  }
  
  @Override
  public void visitElement(XmlContext context, Element element) {
    String value = null;
    NodeList nodes = element.getChildNodes();
    if (nodes.getLength() == 1) {
      // <color> element should have only one node
      Node node = nodes.item(0);
      // This gives us the color, eg. @color/my_awesome_color, #DDFFFF, etc
      value = node.getNodeValue();
    }
    
    if (value == null) {
      // Ideally, this should not happen.
      return;
    }
    
    if (value.startsWith("@color/")) {
      // check if the color name exists in predefined colors.
      if (predefinedColors.contains(value.substring(7))) {
        allowedColors.add(element.getAttribute("name"));
        return;
      }
      
      errorsInAFile++;
      String ignored = element.getAttributeNS(TOOLS_SCHEMA, "ignore");
      if (ignored != null && ignored.contains(ID)) {
        ignoredColors.add(element.getAttribute("name"));
      }
    }
          
    context.report(ISSUE, context.getLocation(element), "custom colors should refer to predefined colors");
  }
  
  @Override
  public void visitAttribute(XmlContext context, Attr attribute) {
    String content = attribute.getTextContent();
    if (content.startsWith("@color/")) {
      if (!predefinedColors.contains(content.substring(7))) {
        // the color is a custom color
        colorUsages.add(Pair.of(attribute, context.getLocation(attribute)));
      }
    } else if (content.startsWith("#")) {
      String ignored = attribute.getOwnerElement().getAttributeNS(TOOLS_SCHEMA, "ignore");
      if (ignored == null || !ignored.contains(ID)) {
        errrosInAFile++;
      }
      context.report(ISSUE, context.getLocation(attribute), "Do not use hardcoded colors");
    }
  }
  
  @Override
  public void afterCheckFile(Context context) {
    if (errorsInAFile == 0) {
      if (context.file.getPath().contains("/res/color")) {
        allowedColors.add(context.file.getName().split("\\.")[0]);
      }
    }
  }
  
  @Override
  public void afterCheckProject(Context context) {
    // filter and report
    for (Pair<Attr, Location> usage: colorUsages) {
      String content = usage.getFirst().getTextContent();
      if (content.startsWith("@color/")) {
        if (!allowedColors.contains(content.substring(7))) {
          context.report(ISSUE, usage.getSecond(), "custom color does not refer to predefined colors");
        }
      } else if (content.startsWith("#")) {
        context.report(ISSUE, usage.getSecond(), "Do not use hardcoded colors");
      }
    }
    
    // clean-up
    allowedColors.clear();
    colorUsages.clear();
    predefinedColors.clear();
  }
}