[build] Reformatter not reaching a fixed point, removed information

[kaby76]

@mike-lischke

This is a problem with the recently added antlr-format. The tool has a bug in reaching a fixed point (i.e., if I take version "before" which is outputed by the tool and rerun the tool on it, the tool should return exactly the same file). In addition it removed a comment that should not have been removed. It's essential that the antlr-format tool outputs a format that reliably follows the coding standard.

Here are four successive versions of PlSqlLexer.g4, the first version the initial. With the second through fourth versions, the START_CMD rule was changed by antlr-format, each time to a different format.

1. Version 7fbb97b, committed 4 months ago.

2. Version 7535367, committed 3 weeks ago. This file is the 1st reformat using antlr-format, which was part of the PR to reformatted all the grammars.

3. Version f083ee2. This file is the 2nd reformat using antlr-format, associated with my PR to perform "auto reformat".

4. Version be1d809. This file is the 3rd reformat using antlr-format, committed 12 hours ago, and associated with a PR to modify PlSql.

Each version of the file was altered only by the tool.

Starting with the 1st version of START_CMD:

grammars-v4/sql/plsql/PlSqlLexer.g4

Lines 2457 to 2463 in 7fbb97b

	// TODO: should starts with newline
	START_CMD
	//: 'STA' 'RT'? SPACE ~('\r' | '\n')* NEWLINE_EOF
	// https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12002.htm
	// https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12003.htm
	: '@''@'?
	;

After 1st application of antlr-format:

grammars-v4/sql/plsql/PlSqlLexer.g4

Lines 2469 to 2474 in 7535367

	// TODO: should starts with newline
	START_CMD
	//: 'STA' 'RT'? SPACE ~('\r' | '\n')* NEWLINE_EOF
	: // https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12002.htm
	'@' '@'?
	; // https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12003.htm

The 2nd application of antlr-format (from my PR) reformats it again.

grammars-v4/sql/plsql/PlSqlLexer.g4

Lines 2469 to 2473 in f083ee2

	// TODO: should starts with newline
	START_CMD
	: // https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12002.htm
	'@' '@'?
	; // https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12003.htm

Finally, the last PR applies antlr-format a third time, changing the rule again.

grammars-v4/sql/plsql/PlSqlLexer.g4

Lines 2469 to 2472 in be1d809

	// TODO: should starts with newline
	START_CMD: // https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12002.htm
	'@' '@'?
	; // https://docs.oracle.com/cd/B19306_01/server.102/b14357/ch12003.htm

Analysis

The comment //: 'STA' 'RT'? SPACE ~('\r' | '\n')* NEWLINE_EOF was removed by antlr-format on the 2nd application of antlr-format. The formatter should not be removing information.

Of the 16 grammar files that were reformatted with my PR. f083ee2 https://github.com/antlr/grammars-v4/actions/runs/7242750577/job/19728583870#step:6:11 , most seem to be minor changes. But, the formatter should output a fixed point version of the grammar on first try. Otherwise I will have to repeat the application until it a fixed point is achieved.

I wrote a script to repeatably apply antlr-format until a fixed point is achieved.

#

rm -rf foo
mkdir foo
pushd foo
cp ../PlSqlLexer.g4.7fbb97b PlSqlLexer.g4
i=1
while :
do
	echo Iteration $i
	cp PlSqlLexer.g4 PlSqlLexer.g4.before
	cp PlSqlLexer.g4 PlSqlLexer.g4.after
	dos2unix *.g4
	antlr-format PlSqlLexer.g4.after 2>&1 1> /dev/null
	dos2unix *.g4
	diff PlSqlLexer.g4.before PlSqlLexer.g4.after
	if [ $? -ne 0 ]
	then
		echo No fixed point yet.
	else
		echo Fixed point achieved.
		break
	fi
	cp PlSqlLexer.g4.after PlSqlLexer.g4
	i=`expr $i + 1`
done

We don't see the fixed point achieved for PlSqlLexer.g4 until 5 applications of antlr-format.
out.txt

What is more troubling is whether there is a grammar (or many) that has (have) no fixed point at all. In this case the tool always produces a new version ad infinitum.

[mike-lischke]

Odd behaviour indeed. Can you move that issue to the antlr-format repository? I'll take a look as soon as I can.

[kaby76]

Moved to antlr-ng/antlr-format#2. Closing this Issue.