Spurious syntax error on process substitution following redirection

[McDutchie]

Gramatically, redirections can occur anywhere within a command line, whereas a process substitution (<(commandlist) or >(commandlist)) is replaced by a file name, so should be treated as just another simple word. So the following should not be a syntax error:

$ cat </dev/null <(true)
-ksh: syntax error: `)' unexpected
$ cat </dev/null >(true)
-ksh: syntax error: `)' unexpected
$ cat >/dev/null <(true)
-ksh: syntax error: `)' unexpected
$ cat >/dev/null >(true)
-ksh: syntax error: `)' unexpected

This bug is in every ksh93 version.

[McDutchie]

Related: #215. Perhaps that bug can be fixed along with this one, once someone figures out the mystical inner workings of the shell parser.

[McDutchie]

The problem appears to be that, after a redirection, the initial ( in a process substitution is simply ignored at the lexical level. The following should clearly be a syntax error, but outputs the contents of README.md:

$ cat </dev/null <(README.md

[McDutchie]

The problem is actually in parse.c, not in lex.c. The process substitution is misparsed as a redirection due to inout(), called from here, recursively parsing multiple redirections without recognising process substitutions. On encountering a process substitution, it should return a special value that causes the caller to go back to where process substitutions are parsed. That's a rather ugly hack, but the alternative is a comprehensive redesign and that is just not going to be realistic any time soon, if ever.

[McDutchie]

This is the best I can come up with, I've been unable to break it:

diff --git a/src/cmd/ksh93/sh/parse.c b/src/cmd/ksh93/sh/parse.c
index 9d290ef4f..17a714218 100644
--- a/src/cmd/ksh93/sh/parse.c
+++ b/src/cmd/ksh93/sh/parse.c
@@ -48,6 +48,7 @@ static Shnode_t	*makeparent(Lex_t*, int, Shnode_t*);
 static Shnode_t	*makelist(Lex_t*, int, Shnode_t*, Shnode_t*);
 static struct argnod	*qscan(struct comnod*, int);
 static struct ionod	*inout(Lex_t*,struct ionod*, int);
+static char		inout_found_procsub;
 static Shnode_t	*sh_cmd(Lex_t*,int,int);
 static Shnode_t	*term(Lex_t*,int);
 static Shnode_t	*list(Lex_t*,int);
@@ -1583,6 +1584,7 @@ static Shnode_t *simple(Lex_t *lexp,int flag, struct ionod *io)
 			lexp->token = tok = 0;
 		if((tok==IPROCSYM || tok==OPROCSYM))
 		{
+	procsub:
 			argp = process_sub(lexp,tok);
 			argno = -1;
 			*argtail = argp;
@@ -1655,6 +1657,8 @@ static Shnode_t *simple(Lex_t *lexp,int flag, struct ionod *io)
 			}
 			else
 				t->comio = io = inout(lexp,(struct ionod*)0,0);
+			if(inout_found_procsub)
+				goto procsub;
 		}
 	}
 	*argtail = 0;
@@ -1753,6 +1757,9 @@ static struct ionod	*inout(Lex_t *lexp,struct ionod *lastio,int flag)
 	Stk_t			*stkp = sh.stk;
 	char *iovname=0;
 	register int		errout=0;
+	/* return if a process substitution is found without a redirection */
+	if(inout_found_procsub = (token==IPROCSYM || token==OPROCSYM))
+		return(lastio);
 	if(token==IOVNAME)
 	{
 		iovname=lexp->arg->argval+1;