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syntax-check: Introduce sc_prohibit_local_with_subshell rule

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In shell, the following function doesn't echo '1' but '0':

  func() {
      local var=$(false)
      echo $?
  }

This is because '$?' does not refer to 'false' but 'local'. The
bash_builtins(1) manpage explains it well. And it also mentions
other commands behaving the same: export, declare and readonly.
Since it is really easy to miss this pattern, introduce a
syntax-check rule. Mind you, the following pattern (which passes
the rule) does check for the subshell exit code:

  func() {
      local var
      var=$(false)
      echo $?
  }

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
This commit is contained in:
Michal Privoznik
2026-01-19 14:22:09 +01:00
parent 2442030856
commit 28482f2630
1 changed files with 11 additions and 0 deletions
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build-aux/syntax-check.mk
+11
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@@ -394,6 +394,17 @@ sc_prohibit_g_autofree_const:
halt='‘g_autofree’ discards ‘const’ qualifier from pointer target type' \
$(_sc_search_regexp)
sc_prohibit_local_with_subshell:
@err=0; for f in $$($(VC_LIST_EXCEPT) | $(GREP) -E '\.sh(\.in)?$$'); do \
lines=$$( $(AWK) \
'/^\s*(local|export|declare|readonly)\s+.*=/ { nr=NR; c=1; next } \
/^\s*$$/ { if (c) next } \
/\$$\?/ { if (c) { print nr; c=0; } next } \
{ c=0 }' $$f ) ; \
for l in $$lines; do echo $$f:$$l 1>&2; err=1; done ; \
done; \
test $$err -eq 0 || { msg="Declare and assign separately to avoid masking return values" $(_sc_say_and_exit) }
# Many of the function names below came from this filter:
# git grep -B2 '\<_('|grep -E '\.c- *[[:alpha:]_][[:alnum:]_]* ?\(.*[,;]$' \