From f3ad5f0dd67ddcfd0429ec0f28325f638e1670f8 Mon Sep 17 00:00:00 2001
From: Frank Mittelbach <frank.mittelbach@latex-project.org>
Date: Wed, 23 Jun 2021 01:02:24 +0200
Subject: [PATCH] fix for #586; expecting #591 to change the version number

---
 required/firstaid/changes.txt                 |  3 ++-
 .../latex2e-first-aid-for-external-files.dtx  |  2 +-
 .../testfiles/firstaid-ulem-varwidth.lvt      | 19 ++++++++++++++++++-
 .../testfiles/firstaid-ulem-varwidth.tlg      |  3 ++-
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/required/firstaid/changes.txt b/required/firstaid/changes.txt
index 634e3e5c9..28988e9a3 100644
--- a/required/firstaid/changes.txt
+++ b/required/firstaid/changes.txt
@@ -2,7 +2,8 @@
 
 	* latex2e-first-aid-for-external-files.dtx:
 	ulem doesn't handle \hspace gracefully now that it is calc aware.
-	varwidth needs an additional \unskip when unraveling a vertical list.
+	varwidth needs an additional \unskip when unraveling a vertical list
+	(but only if that skip is 0pt)
 
 2021-03-15  Frank Mittelbach  <Frank.Mittelbach@latex-project.org>
 
diff --git a/required/firstaid/latex2e-first-aid-for-external-files.dtx b/required/firstaid/latex2e-first-aid-for-external-files.dtx
index 84ddacb26..03c6ce360 100644
--- a/required/firstaid/latex2e-first-aid-for-external-files.dtx
+++ b/required/firstaid/latex2e-first-aid-for-external-files.dtx
@@ -583,7 +583,7 @@
      {%
 \def\@vwid@sift{%
   \skip@\lastskip\unskip
-  \unskip                         % <---- the first aid here
+  \ifdim\lastskip=\z@\unskip\fi   % <---- the first aid here (not just unskip)
   \dimen@\lastkern\unkern
   \count@\lastpenalty\unpenalty
   \setbox\z@\lastbox
diff --git a/required/firstaid/testfiles/firstaid-ulem-varwidth.lvt b/required/firstaid/testfiles/firstaid-ulem-varwidth.lvt
index 35bd7cb64..b8aab5a86 100644
--- a/required/firstaid/testfiles/firstaid-ulem-varwidth.lvt
+++ b/required/firstaid/testfiles/firstaid-ulem-varwidth.lvt
@@ -16,6 +16,9 @@
 
 \uline{{\hspace{1cm}}}
 
+\bigskip
+
+
 \setbox0\hbox{%
   x
   \begin{varwidth}[t]{10cm}
@@ -24,7 +27,21 @@
   x
 }
 
-\typeout{same baseline please: \the\ht0 + \the\dp0}
+\typeout{same baseline please: \the\ht0 \space + \the\dp0}
+
+\unhbox0  % visual check only
+
+\bigskip
+
+\setbox0\hbox{%
+\fbox{\begin{varwidth}[t]{3cm}
+some text
+\par
+\vskip-\baselineskip\vbox{\hbox{\strut}}%
+\end{varwidth}}%
+}
+
+\typeout{shoule not contain extra empty line: \the\ht0 \space + \the\dp0}
 
 \unhbox0  % visual check only
 
diff --git a/required/firstaid/testfiles/firstaid-ulem-varwidth.tlg b/required/firstaid/testfiles/firstaid-ulem-varwidth.tlg
index aaa7e95b5..d7433021a 100644
--- a/required/firstaid/testfiles/firstaid-ulem-varwidth.tlg
+++ b/required/firstaid/testfiles/firstaid-ulem-varwidth.tlg
@@ -1,6 +1,7 @@
 This is a generated file for the l3build validation system.
 Don't change this file in any respect.
 no error please:
-same baseline please: 6.94444pt+ 0.0pt
+same baseline please: 6.94444pt + 0.0pt
+shoule not contain extra empty line: 9.55078pt + 7.00003pt
 [1
 ] (firstaid-ulem-varwidth.aux)