bug symfony#57853 [Console] Fix side-effects from running bash completions (Seldaek)

This PR was merged into the 5.4 branch.

Discussion
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[Console] Fix side-effects from running bash completions

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | Fix composer/composer#12015
| License       | MIT

Fixes issues in symfony bash completions having side-effects for other completions. See composer/composer#12015 for details.

I identified this IFS line as causing the issue.. But it was introduced here
symfony@e9e0c07 (cc `@GromNaN`) probably for a good reason. So I don't think this is mergeable as is, but we should see what can be done to set IFS where needed per process call and not change it globally like that.

Commits
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5456645 [Console] Fix side-effects from running bash completions

Author: nicolas-grekas

src/Symfony/Component/Console/Resources/completion.bash

@@ -7,7 +7,7 @@
 
 _sf_{{ COMMAND_NAME }}() {
     # Use newline as only separator to allow space in completion values
-    IFS=$'\n'
+    local IFS=$'\n'
     local sf_cmd="${COMP_WORDS[0]}"
 
     # for an alias, get the real script behind it