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Eclipse-Formatter-Plugin fails due to wrong assumptions

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
java
Domain
tooling

Research direction

Start by reproducing the minimal Test class with the Eclipse API snippet, then read SnippetFormatter.java and its toReplacements() method. Trace how the non-whitespace comparison leads to the Eclipse formatter returning null. Done means the sample source can be formatted through the plugin without this failure, with the behavior verified by a regression test.

Written by the indexing model from the issue text.

Description

Eclipse

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.

Dominant language
Java
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Merged PRs (30d)
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