Stabilize XML declaration formatting on reformat#1009
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The XMLDeclOpen token ("<?xml") carries the single whitespace character
that follows it, since its lexer pattern is /<\?xml[ \t\r\n]/. Printing that
character verbatim is not stable: when the declaration wraps onto multiple
lines, the captured character is a newline, and re-formatting then renders an
extra blank line right after "<?xml". As a result prettier's own output of a
wrapped declaration is not idempotent and fails prettier --check.
Print a normalized "<?xml" and let the surrounding layout provide the
spacing, so a wrapped declaration round-trips unchanged.
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Running the plugin on its own output isn't stable when the XML declaration wraps. If a
<?xml … ?>declaration is long enough (orprintWidthsmall enough) to break onto multiple lines, the first pass producesbut a second pass inserts a blank line right after
<?xml:So formatted files don't pass
prettier --check.The cause is in
printProlog: theXMLDeclOpentoken's image isn't just<?xml— its lexer pattern is/<\?xml[ \t\r\n]/, so it also carries the one whitespace character that follows. We print that character verbatim. On a wrapped declaration that character is a newline, and printing it ahead of the line break that begins the attributes yields the extra blank line.I print a normalized
<?xmland let the existing layout supply the spacing (the leadingsoftlinebecomes alineso the single-line case keeps its space). The common single-line output is unchanged, and a wrapped declaration now round-trips. Added a test that formats a wrapped declaration twice and asserts the second pass is a no-op.