Eclipse-Formatter-Plugin fails due to wrong assumptions

まず Eclipse API スニペットを使って最小限の Test クラスを再現し、次に SnippetFormatter.java とその toReplacements() メソッドを読みます。空白を除いた比較によって Eclipse formatter が null を返すに至る流れを追跡します。サンプルソースをこの失敗なしに plugin 経由でフォーマットでき、その動作が regression test で検証されれば完了です。

The Eclipse-Plugin has sometimes a problem when I call the formatter programatically inside Eclipse. I am using the Snippet from https://help.eclipse.org/latest/topic/org.eclipse.jdt.doc.isv/guide/jdt_api_codeformatter.htm to format a complete Java-File. I have created a minimal Test-Class:

package test;

/**
 * Test Class
 * 
 * Generated
 * 
 */
public class Test
{
}

The standalone-Formatter-Jar adds a HTML-Tag

before the "Generated". Unfortunately, when I call the plugin via the Eclipse-APIs:

    final TextEdit edit =
        codeFormatter.format(
            CodeFormatter.K_COMPILATION_UNIT, // format a compilation unit
            content, // source to format
            0, // starting position
            content.length(), // length
            0, // initial indentation
            "\r\n" // line separator
            );

the method returns a null because it can not format the content. I have tracked the problem back to the class SnippetFormatter.java, Method toReplacements(). This method has the condition which checks the unformatted and the formatted source:

if (!NOT_WHITESPACE.retainFrom(source).equals(NOT_WHITESPACE.retainFrom(replacement))) {
      throw new IllegalArgumentException(
          "source = \"" + source + "\", replacement = \"" + replacement + "\"");
    }

This condition checks that there are only whitespace-changes in the new formatted source. The Javadoc says:

under the assumption that they differ in whitespace alone.

Unfortunately, this assumption is not correct. The source has (as mentioned above) an additional non-whitespace change and the IllegalArgumentException is thrown. This Exception causes the Eclipse-Formatter-Class to fail and to return only null, thereby denying to format the source.