This fixes erroneous syntax errors in parameter expansions such as

${var:-wor)d} or ${var+w(ord}. The parentheses now correctly lose
their normal grammatical meaning within the braces. Fix by Eric
Scrivner (@etscrivner) from July 2018 backported from ksh2020.

This fix complies with POSIX:
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02

src/cmd/ksh93/sh/lex.c: sh_lex():
- Set the ST_QUOTE state when analysing a modifier with parameter
  expansions using operators ':', '-', '+', '='. This state causes
  subsequent characters (including parentheses) to be considered
  quoted, suppressing their normal grammatical meaning.

src/cmd/ksh93/sh/macro.c: varsub():
- Same for skipping the expansion.

Fixes: https://github.com/ksh93/ksh/issues/126
Prior discussion: https://github.com/att/ast/issues/475

NEWS

@@ -3,6 +3,12 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-09-05:
+
+- Fixed erroneous syntax errors in parameter expansions such as ${var:-wor)d}
+  or ${var+w(ord}. The parentheses now correctly lose their normal grammatical
+  meaning within the braces. Fix by Eric Scrivner backported from ksh2020.
+
 2020-09-04:
 
 - Fixed a bug that caused a syntax error to be thrown if the special parameter