Restore . alias for source

The breakage is just too annoying.

This reverts 55bef3cd2e.

CHANGELOG.md

@@ -9,7 +9,6 @@ This section is for changes merged to the `major` branch that are not also merge
 - `?` as a glob is deprecated and will be removed in the future. (#4520). This is controlled by the `qmark-noglob` feature flag.
 
 ## Notable non-backward compatible changes
-- `.` command no longer exists -- use `source` (#4294).
 - `read` now uses `-s` as short for `--silent` (à la `bash`); `--shell`'s abbreviation (formerly `-s`) is now `-S` instead (#4490).
 - `set x[1] x[2] a b` is no longer valid syntax (#4236).
 - `for` loop control variables are no longer local to the `for` block (#1935).

share/config.fish

@@ -172,6 +172,18 @@ end
 # in UTF-8 (with non-ASCII characters).
 __fish_set_locale
 
+# "." command for compatibility with old fish versions.
+function . --description 'Evaluate contents of file (deprecated, see "source")' --no-scope-shadowing
+    if test (count $argv) -eq 0
+        # Uses tty directly, as isatty depends on "."
+        and tty 0>&0 >/dev/null
+        echo "source: '.' command is deprecated, and doesn't work with STDIN anymore. Did you mean 'source' or './'?" >&2
+        return 1
+    else
+        source $argv
+    end
+end
+
 # As last part of initialization, source the conf directories.
 # Implement precedence (User > Admin > Extra (e.g. vendors) > Fish) by basically doing "basename".
 set -l sourcelist