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cpp: fix mutually recursive macros

Handle cases where parameterless macros expand to each other:

	#define FOO BAR
	#define BAR FOO
	FOO

There were cases where the macros didn't make it into the hidesets,
and we would recurse infinitely. This fixes that.

--- a/sys/src/cmd/cpp/cpp.h

+++ b/sys/src/cmd/cpp/cpp.h

@@ -110,7 +110,7 @@

 void	expand(Tokenrow *, Nlist *);

 void	builtin(Tokenrow *, int);

 int	gatherargs(Tokenrow *, Tokenrow **, int, int *);

-void	substargs(Nlist *, Tokenrow *, Tokenrow **);

+void	substargs(Nlist *, Tokenrow *, Tokenrow **, int);

 void	expandrow(Tokenrow *, char *);

 void	maketokenrow(int, Tokenrow *);

 Tokenrow *copytokenrow(Tokenrow *, Tokenrow *);

--- a/sys/src/cmd/cpp/macro.c

+++ b/sys/src/cmd/cpp/macro.c

@@ -169,9 +169,8 @@

 		}

 		if (np->flag&ISMAC)

 			builtin(trp, np->val);

-		else {

+		else

 			expand(trp, np);

-		}

 		tp = trp->tp;

 	}

 	if (flag)

@@ -186,11 +185,10 @@

 void

 expand(Tokenrow *trp, Nlist *np)

 {

+	int ntokc, narg, i, hs;

+	Tokenrow *atr[NARG+1];

 	Tokenrow ntr;

-	int ntokc, narg, i;

 	Token *tp;

-	Tokenrow *atr[NARG+1];

-	int hs;

 	copytokenrow(&ntr, np->vp);		/* copy macro value */

 	if (np->ap==NULL) {			/* parameterless */

@@ -197,7 +195,7 @@

 		ntokc = 1;

 		/* substargs for handling # and ## */

 		atr[0] = nil;

-		substargs(np, &ntr, atr);

+		substargs(np, &ntr, atr, trp->tp->hideset);

 	} else {

 		ntokc = gatherargs(trp, atr, (np->flag&ISVARMAC) ? rowlen(np->ap) : 0, &narg);

 		if (narg<0) {			/* not actually a call (no '(') */

@@ -210,12 +208,13 @@

 			trp->tp += ntokc;

 			return;

 		}

-		substargs(np, &ntr, atr);	/* put args into replacement */

+		substargs(np, &ntr, atr, trp->tp->hideset);	/* put args into replacement */

 		for (i=0; i<narg; i++) {

 			dofree(atr[i]->bp);

 			dofree(atr[i]);

 		}

 	}

+

 	hs = newhideset(trp->tp->hideset, np);

 	for (tp=ntr.bp; tp<ntr.lp; tp++) {	/* distribute hidesets */

 		if (tp->type==NAME) {

@@ -343,12 +342,13 @@

 	}

 	return 0;

 }

+

 /*

  * substitute the argument list into the replacement string

  *  This would be simple except for ## and #

  */

 void

-substargs(Nlist *np, Tokenrow *rtr, Tokenrow **atr)

+substargs(Nlist *np, Tokenrow *rtr, Tokenrow **atr, int hideset)

 {

 	Tokenrow ttr, rp, rn;

 	Token *tp, *ap, *an, *pp, *pn;

@@ -355,7 +355,7 @@

 	int ntok, argno, hs;

 	for (rtr->tp=rtr->bp; rtr->tp<rtr->lp; ) {

-		if(rtr->tp->hideset && checkhideset(rtr->tp->hideset, np)) {

+		if(rtr->tp->hideset && checkhideset(hideset, np)) {

 			rtr->tp++;

 		} else if (rtr->tp->type==SHARP) {	/* string operator */

 			tp = rtr->tp;

@@ -405,10 +405,10 @@

 				*ttr.tp = *rtr->tp;

 				hs = newhideset(rtr->tp->hideset, np);

-				if(ttr.tp->hideset == 0)

+				if(hideset == 0)

 					ttr.tp->hideset = hs;

 				else

-					ttr.tp->hideset = unionhideset(ttr.tp->hideset, hs);

+					ttr.tp->hideset = unionhideset(hideset, hs);

 				expandrow(&ttr, (char*)np->name);

 				for(tp = ttr.bp; tp != ttr.lp; tp++)

 					if(tp->type == COMMA)