UseThemeFriendlyColorsInXmlDetector.kt

/**
 * Prohibits use of hardcoded colors in XML layouts and color resources.
 *
 * A hardcoded color includes:
 *
 * - a reference to a color resource which doesn't include "mds" in the name.
 *   "mds" is used as an allowlist filter, where we'll assume that the resource contains theme-friendly colors
 *   or it's an exception to the rule.
 * - a color hexcode
 *
 * It's relatively important to keep this up-to-date with `HardcodedColorsDesignStatsProcessor` so that our stats
 * tracking is kept reasonably accurate.
 */
internal class UseThemeFriendlyColorsInXmlDetector : ResourceXmlDetector() {

    companion object {
        val ISSUE = createErrorThemesAndStylesIssue(
                UseThemeFriendlyColorsInXmlDetector::class,
                Scope.RESOURCE_FILE_SCOPE
        )
    }

    override fun appliesTo(folderType: ResourceFolderType) =
            folderType == LAYOUT || folderType == VALUES || folderType == COLOR

    override fun getApplicableAttributes(): Collection<String> = XmlScannerConstants.ALL

    override fun visitAttribute(context: XmlContext, attribute: Attr) {
        when (context.resourceFolderType) {
            COLOR, LAYOUT -> if (attribute.value.isColorHexcode() || attribute.value.isHardcodedColorResInXml()) {
                reportIssue(context, attribute)
            }
            VALUES -> {
                // we're only interested in style resources
                val item = if (attribute.belongsToItem()) attribute.ownerElement else return
                if (item.belongsToThemeOrThemeOverlay()) {
                    // we define attributes in themes/theme overlays so it's normal to have hardcoded colors here
                    // kind of, maybe
                    return
                }
                if (item.belongsToStyle()) {
                    val value = item.firstChild.nodeValue
                    if (value.isColorHexcode() || value.isHardcodedColorResInXml()) {
                        reportIssue(context, attribute)
                    }
                }
            }
        }
    }

    private fun reportIssue(context: XmlContext, attribute: Attr) {
        context.report(
                issue = ISSUE,
                scope = attribute,
                location = context.getValueLocation(attribute),
                message = "Avoid using hardcoded colors."
        )
    }
}

// These symbols are duplicated in `HardcodedColorsDesignStatsProcessor`
private val REGEX_HEX_COLOR = Regex("^#[0-9a-fA-F]{8}$|#[0-9a-fA-F]{6}$|#[0-9a-fA-F]{4}$|#[0-9a-fA-F]{3}$")

private fun String.isColorHexcode() = REGEX_HEX_COLOR.containsMatchIn(this)

/**
 * "mds" is used as an allowlist filter, where we'll assume that the resource contains theme-friendly colors
 *  or it's an exception to the rule.
 */
private fun String.isHardcodedColorResInXml() = startsWith("@color/") && !contains("mds")