I tried this patch on and MacOS11/iterm2 and RHEL 7 (ssh'd from the Mac, in case that matters) and the example shown at the top of the thread shows no difference:
john.naylor=# \pset border 2
Border style is 2.
john.naylor=# SELECT U&'\+01F603';
+----------+
| ?column? |
+----------+
| 😃 |
+----------+
(1 row)
(In case it doesn't render locally, the right bar in the result cell is still shifted to the right.
What is the expected context to show a behavior change? Does one need some specific terminal or setting?
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