[pdftex] microtype problem with logos in new pdftex?

[Karl Berry]

Hi Thanh and all - I think there is some unexpected change relating to
microtype (somehow) in the new pdftex. When I run pdflatex-2025 on the
attached simple LaTeX document, the T and the E of the \TeX logo at the
end of the first line crash together.

The crashing does not happen with lualatex-2025 or pdflatex-2024.  But
it does still happen with pdftex-2025 + the 2024 TeX tree, i.e., with an
older microtype, which is what makes me think it is a change in the
engine and not in microtype.

I noticed this with the TL Guide. It happens many more times in the full
document, sometimes with even worse results. I'll attach the full pdf
here also, just in case (several squished logos on page 5, an extra
space after the T on pages 6 and 8, etc.). Also committed to the TL repo.

But ... what I don't understand is the typesetting results in the .log
file (with \loggingall) are identical between pdflatex-2024 and
pdflatex-2025. Naturally there are plenty of changes in the macro
expansions, but the "Completed box being shipped out [1]" output is
identical; the critical section excerpted below. So ... something in the
PDF that is not related to the TeX processing? Somehow?

I tried two PDF readers, evince and xpdf, and they both had the same
results. PDF-1.7 vs. 1.5 doesn't seem to matter either.

Help? --thanks, karl.

..\hbox(8.33331+2.66666)x420.17853, glue set - 0.92131, shifted 29.3747
[omitted]
...\glue 3.91663 plus 1.95831 minus 1.30554
...\OT1/cmr/m/n/12 (-20) T
...\kern -1.95872
...\hbox(8.2+0.0)x7.99437, shifted 2.58333
....\OT1/cmr/m/n/12 E

-------------- next part --------------
A non-text attachment was scrubbed...
Name: test.tex
Type: application/octet-stream
Size: 410 bytes
Desc: not available
URL: <https://tug.org/pipermail/pdftex/attachments/20250212/3c1463f4/attachment-0001.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: luatex25.pdf
Type: application/pdf
Size: 11000 bytes
Desc: not available
URL: <https://tug.org/pipermail/pdftex/attachments/20250212/3c1463f4/attachment-0004.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: pdftex24.pdf
Type: application/pdf
Size: 30197 bytes
Desc: not available
URL: <https://tug.org/pipermail/pdftex/attachments/20250212/3c1463f4/attachment-0005.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: pdftex25.pdf
Type: application/pdf
Size: 30232 bytes
Desc: not available
URL: <https://tug.org/pipermail/pdftex/attachments/20250212/3c1463f4/attachment-0006.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: texlive-en.pdf
Type: application/pdf
Size: 1087822 bytes
Desc: not available
URL: <https://tug.org/pipermail/pdftex/attachments/20250212/3c1463f4/attachment-0007.pdf>