QET::splitWithSpaces() split on QRegularExpression("[^\\]?(?:\\\\)* ").
That is not a valid pattern: "[^\\]" opens a character class whose "\\]" is
an escaped bracket, so the class is never closed. QRegularExpression
reported isValid() == false, QString::split() warned "invalid
QRegularExpression object", and the function returned an EMPTY list for
every input.
It is the receiving half of the SingleApplication handshake: a secondary
instance sends "launched-with-args: " + joinWithSpaces(args) (main.cpp) and
the running instance parses it in QETApp::receiveMessage() before calling
openFiles(). With the split always empty, the running instance received no
arguments at all -- so opening a project while QET was already running
silently did nothing.
The bug is reported against filenames containing spaces, which is how it
was noticed, but it is not limited to them: plain names failed identically.
A corrected regex is not available. The separator is a space preceded by an
even-length run of backslashes, and PCRE2 has no variable-length lookbehind,
so the run cannot be expressed in a lookbehind and anything that matches it
by consumption eats the character before the space -- which is what the
"[^\\]?" was for. Scanning the string explicitly is correct and easier to
read.
tests/qttest/tst_qetstrings.cpp asserts the round trip
splitWithSpaces(joinWithSpaces(x)) == x over plain names, embedded spaces,
embedded backslashes, a trailing backslash and a mixture, plus the specific
regression that a plain argument list does not come back empty.
Verified the test fails without the fix: 9 of 11 cases fail on the old
implementation and all 11 pass with it. Full suite 5/5, Qt 5.15.18.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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