[abashev]

Fixes #171.

What happens

A comment on its own line right after an opening delimiter came out at the indent of the statement, and so did the code after it. The delimiters are for (, the ( of a try with several resources and of a multi-catch clause, the < of explicit type arguments (new <String>T(), T::<String>g), assert with a detail message, and the ; that ends the constants of an enum. For the enum, the comment and the ; even landed in the enum's own column.

Input:

class T {
  void f(int n) {
    for (
      // comment
      int i = 0; i < n; i++) {}
  }
}

enum E {
  A,
    // comment
    ;
}

Before:

class T {
    void f(int n) {
        for (
        // comment
        int i = 0; i < n; i++) {}
    }
}

enum E {
    A,
// comment
;
}

After:

class T {
    void f(int n) {
        for (
                // comment
                int i = 0;
                i < n;
                i++) {}
    }
}

enum E {
    A,
    // comment
    ;
}

Why

OpsBuilder.build places the comments before a token ahead of the OpenOps right before it, so that a comment before a statement or an expression stays out of their levels. Each of these delimiters opens the level that indents what follows it right before that level's first token. The comment therefore left the level, and the forced break after the comment took the next line out with it.

google/google-java-format#1501 fixes the same defect in google-java-format's new layout builder (groundwork in google/google-java-format#1500, baseline cases in google/google-java-format#1502). Its code does not apply to our engine, but the idea does.

The fix

• OpsBuilder.fenceComments() adds a marker that build stops at when it looks back over OpenOps, and drops before the ops become a Doc.
• The six places call it right after they open their level, as upstream does: visitAssert, the ; after enum constants, visitForLoop, visitTry, visitCatchClause and addTypeArguments.
• The comment now breaks the level it sits in. The parts of a for header and the : of an assert get a line each, as they do whenever that level breaks.
• An assert without a detail message and a try with one resource open a level without indent, so their comments stay where they were.
• A block comment that shares its line with the code after it stays with it, on the line of the delimiter when that fits: for (/* c */ int i = 0; i < n; i++) {}.

Tests

There are six new cases, test-cases/commentAfterOpeningDelimiter-{assert,enumSemicolon,forHeader,tryResources,multiCatch,typeArguments}.case. Each input mixes upstream's shape, the shape 21.X.X produces today, and odd breaks and spacing. All six failed on the unchanged code with the comment at the statement's indent, and they pass with the fix, including the second run.

On JDK 21:

• FormatterCasesTest: 887 → 893.
• The module: 1408 → 1414 tests, 14 skipped.
• ./gradlew test --rerun is green for all modules (Gradle plugin 51 tests, IntelliJ plugin 10).

JDK corpus

None of the 15,747 files of the JDK 21 sources formats differently. None of them has a comment on its own line after one of these delimiters.