sh: Do not allow overriding a special builtin with a function.

This is a syntax error.

POSIX does not say explicitly whether defining a function with the same name
as a special builtin is allowed, but it does say that it is impossible to
call such a function.

A special builtin can still be overridden with an alias.

This commit is part of a set of changes that will ensure that when
something looks like a special builtin to the parser, it is one. (Not the
other way around, as it remains possible to call a special builtin named
by a variable or other substitution.)

Exp-run done by:	pav (with some other sh(1) changes)

1 files changed, 7 insertions, 0 deletions

diff --git a/tools/regression/bin/sh/execution/func3.0 b/tools/regression/bin/sh/execution/func3.0
new file mode 100644
index 0000000..f7a562a
--- /dev/null
+++ b/tools/regression/bin/sh/execution/func3.0
@@ -0,0 +1,7 @@
+# $FreeBSD$
+
+# This may fail when parsing or when defining the function, or the definition
+# may silently do nothing. In no event may the function be executed.
+
+sh -c 'unset() { echo overriding function executed, bad; }; v=1; unset v; exit "${v-0}"' 2>/dev/null
+: