Fix wrong syntax error upon process substitution after redirection

Grammatically, redirections may occur anywhere within a command
line and are removed after processing them, whereas a process
substitution (<(commandlist) or >(commandlist)) is replaced by a
file name which 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.

The problem is in the parser (parse.c). The process substitution is
misparsed as a redirection due to inout() recursively parsing
multiple redirections without recognising process substitutions.
inout() is mistaking '<(' for '<' and '>(' for '>', which explains
the incorrect syntax error.

This also causes the following to fail to detect a syntax error:
$ cat >&1 <(README.md
[the contents of README.md are shown]

...and other syntax errors detected in the wrong spot, for example:
$ { true; } <(echo wrong)
-ksh: syntax error: `wrong' unexpected
which should be:
-ksh: syntax error: `<(' unexpected

src/cmd/ksh93/sh/parse.c:
- Add global inout_found_procsub flag.
- inout(): On encountering a process substitution, set this flag
  and return, otherwise clear the flag.
- simple(): After calling inout(), check this flag and, if set,
  jump back to where process substitutions are parsed.

Resolves: #418

NEWS

@@ -3,6 +3,12 @@ For full details, see the git log at: https://github.com/ksh93/ksh/tree/1.0
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2022-07-05:
+
+- Fixed a spurious syntax error on encountering a process substitution
+  following a redirection without being an argument to a redirection.
+  For example, this now writes 'OK' to standard error: cat >&2 <(echo OK)
+
 2022-07-02:
 
 - Fixed a bug where, if the last command in a subshell was an external

src/cmd/ksh93/include/version.h

@@ -23,7 +23,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.0-beta.2"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2022-07-02"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2022-07-05"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2022 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

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;

src/cmd/ksh93/tests/io.sh

@@ -974,5 +974,35 @@ then
 		"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 fi
 
+# ======
+# A process substitution should be valid after a redirection
+# https://github.com/ksh93/ksh/issues/418
+got=$(set +x; eval ': </dev/null <(true)' 2>&1)
+[[ e=$? -eq 0 && -z $got ]] || err_exit "spurious syntax error on process substitution following redirection" \
+	"(expected status 0 and '', got status $e and $(printf %q "$got"))"
+got=$(set +x; eval ': <&1 <(/dev/null' 2>&1)
+exp='*: syntax error at line *: `end of file'\'' unexpected'
+[[ $got == $exp ]] || err_exit "': <&1 <(/dev/null' fails to throw a syntax error" \
+	"(expected match of $(printf %q "$exp"), got $(printf %q "$got"))"
+got=$(set +x; eval '{ :; } <(: wrong)' 2>&1)
+exp='*: syntax error at line *: `<('\'' unexpected'
+[[ $got == $exp ]] || err_exit "'{ :; } <(: wrong)' throws incorrect syntax error" \
+	"(expected match of $(printf %q "$exp"), got $(printf %q "$got"))"
+got=$(set +x; eval ': >/dev/null >(true)' 2>&1)
+[[ e=$? -eq 0 && -z $got ]] || err_exit "spurious syntax error on process substitution following redirection" \
+	"(expected status 0 and '', got status $e and $(printf %q "$got"))"
+got=$(set +x; eval ': >&1 >(/dev/null' 2>&1)
+exp='*: syntax error at line *: `end of file'\'' unexpected'
+[[ $got == $exp ]] || err_exit "': >&1 >(/dev/null' fails to throw a syntax error" \
+	"(expected match of $(printf %q "$exp"), got $(printf %q "$got"))"
+got=$(set +x; eval '{ :; } >(: wrong)' 2>&1)
+exp='*: syntax error at line *: `>('\'' unexpected'
+[[ $got == $exp ]] || err_exit "'{ :; } >(: wrong)' throws incorrect syntax error" \
+	"(expected match of $(printf %q "$exp"), got $(printf %q "$got"))"
+got=$(set +x; eval 'cat >out <(echo OK)' 2>&1; echo ===; cat out)
+exp=$'===\nOK'
+[[ $got == "$exp" ]] || err_exit "process substitution nixes output redirection" \
+	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
+
 # ======
 exit $((Errors<125?Errors:125))