报告位置

Issue Location

通过 JavaContext.report 方法来报告一个 Issue ，我们需要提供 Issue 的位置。大部分情况，我们都可以通过 JavaContext.getNameLocation 或者 JavaContext.getLocation 方法来获取语法树节点的位置。

Location 中有几个重要的属性，其中 start 和 end 之间的范围就是该 Issue 在 IDE 中提示的代码位置：

/**
 * Returns the file containing the warning. Note that the file *itself* may
 * not yet contain the error. When editing a file in the IDE for example,
 * the tool could generate warnings in the background even before the
 * document is saved. However, the file is used as a identifying token for
 * the document being edited, and the IDE integration can map this back to
 * error locations in the editor source code.
 *
 * @return the file handle for the location
 */
val file: File
/**
 * The start position of the range
 *
 * @return the start position of the range, or null
 */
val start: Position?
/**
 * The end position of the range
 *
 * @return the start position of the range, may be null for an empty range
 */
val end: Position?
/**
 * Returns a secondary location associated with this location (if
 * applicable), or null.
 */
open var secondary: Location? = null

secondary 可以帮我们连接两个 Location ，比如我们检测资源文件的使用时，既要定位出代码中的行数，也要定位出资源文件中的位置：

Linked Location

Location secondary = context.getLocation(previous);
secondary.setMessage("另一个位置");
location.setSecondary(secondary);

除了从 UElement 或者 PsiElement 中直接获取 Location ，当然我们也可以自己去计算和定义具体的行数和列数：

Pair<Integer, Integer> offsets = getOffsets(node, context);
int fromLine = node.getLineNumber() - 1;
int fromColumn = node.getColumnNumber() - 1;
int toLine = node.getLastLineNumber() - 1;
int toColumn = node.getLastColumnNumber() - 1;
return Location.create(context.file,
        new DefaultPosition(fromLine, fromColumn, offsets.getFirst()),
        new DefaultPosition(toLine, toColumn, offsets.getSecond()));