Leave JBang directives at the top of a file as written - #91

Closes #24. The same problem is open upstream as google/google-java-format#1217, raised by JBang's author, and for the first line as google/google-java-format#1215 and google/google-java-format#1218. jbangdev/jbang#1194 asked JBang to accept // DEPS instead and was closed: a formatter should not add a space where there was none.

The bug

JBang reads a script's configuration from line comments with the directive name right after the slashes, and a shell runs the first line when the file is executed. The formatter put a space after the slashes of every line comment and wrapped the long ones:

/// usr/bin/env jbang "$0" "$@" ; exit $?
// JAVA 21+
// DEPS info.picocli:picocli:4.7.6
// DEPS com.fasterxml.jackson.core:jackson-databind:2.17.2 org.slf4j:slf4j-simple:2.0.13
// com.squareup.okhttp3:okhttp:4.12.0 org.jsoup:jsoup:1.18.1
// JAVA_OPTIONS -Xmx512m

JBang no longer saw any of it. The dependencies, the Java version and the options were dropped without a word, and a shell tried to run ///, which is a directory.

Where directives count

JBang's directives reference says a directive "must be in the first comment block of the file (before any code)". Its parser is more lenient: Directives.Extended.getAll reads every line of the file that starts with // at column 0. JBang's own tests rely on that: they put //SOURCES between package and import and //RUNTIME_OPTIONS after the imports.

This change follows the documented rule, which keeps the exemption narrow. A directive after the first line of code is formatted like any other comment, as before.

The fix

JavaCommentsHelper leaves two kinds of line comment exactly as written, with no space after the slashes and no wrapping, when they come before the first token of the file:

• a directive: one of the 22 names in JBang's Directives.Names, or a name with an integration prefix such as Quarkus's //Q:CONFIG, followed by whitespace or the end of the line;
• the shell line: the first line of the file, when its first word is a path, as in ///usr/bin/env, //usr/bin/env or the long self-bootstrapping header from JBang's docs.

The helper now takes the JavaInput. Comments are numbered along with tokens, so the index of the first token tells which comments come before any code. Header comments always go through the helper, so Comment.computeFlat(), the path behind #23, is not involved.

What stays as before:

• //DEPSSS, //deps, //DEPS:x, //JAVA21+, ///DEPS and //TODO get their space everywhere, and JBang ignores them too.
• // DEPS and // //DEPS are left alone. JBang's own templates switch an optional dependency off with the second form.
• After package, an import or a class, //DEPS becomes // DEPS and is wrapped like any other comment.

Checked

• Three goldens, each with its code left unformatted in the input:
  • ojf-issue-24-jbang-script: the script from the issue, plus directives between and after the imports, in the class, after a statement and after the class;
  • ojf-issue-24-jbang-package: the bootstrap header, a license comment, //Q:CONFIG, a tab after the name and a directive after package;
  • ojf-issue-24-jbang-compact-source: //usr/bin/env and a compact source file, gated at JDK 21 like CompactSource.
• JBangDirectivesTest covers:
  • every directive name;
  • the syntax JBang allows after a name: a tab, a trailing // comment, a ${...} property, no value, and a line longer than 120 columns;
  • the lookalikes above;
  • a shell line after a license comment, and a first line without a path.
• On main's code the goldens and the 28 kept-as-written cases fail. The ten lookalikes and the two shell-line cases pass on both, since they pin the exemption down.
• ./gradlew :open-java-format:test on JDK 21: 1597 tests, all green, 12 skipped (the JDK 23+ module import tests).
• The CLI fixes imports before it formats, and that pass keeps a directive above the imports where it was.
• The 15,747 files of the JDK 21 sources format exactly as before; none of them has a directive or a shell line.

Version

Only lines that come out broken today, a directive JBang no longer reads or a first line the shell cannot run, format differently. That makes this a bug fix in the 2.x sense, although the output for such files now differs from palantir-java-format 2.98.0.