Take a look at this example:

(format (concat "%s" (propertize "%s" 'face 'error)) "foo" "bar")

(format (concat "%s " (propertize "%s" 'face 'error)) "foo" "bar")
#("foo bar" 4 7 (face error))

And the documentation of format explicitly states:

Text properties, if any, are copied from the format-string to the produced text.

Why is that?

I know I can work around this with:

(format "%s%s" "foo" (propertize "bar" 'face 'error))
#("foobar" 3 6 (face error))

Or even:

(concat "foo" (propertize "bar" 'face 'error))
#("foobar" 3 6 (face error))

But my original use case is a bit more complex than this.


A probably more general example is the following:

(format (concat (propertize "%s" 'face 'bold)
                "" ; any non-empty string works
                (propertize "%s" 'face 'error))
        "foo" "bar")
#("foobar" 0 6 (face bold))
  • Looks like a bug, or an enhancement request. Wait a bit, to see what others say, then consider filing a bug report: M-x report-emacs-bug. – Drew Aug 6 '18 at 18:03
  • Observation: Text properties are copied only when there is a literal character in the format string, e.g., (format (propertize "\s%s" 'face 'error) "foo") gives #(" foo" 0 4 (face error)). – Tobias Aug 8 '18 at 13:35
  • @Tobias No I think it's more about literals between two otherwise adjacent %-sequences. – cYrus Aug 8 '18 at 13:49

So it was a bug which has now been fixed in this commit.

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