gc: add error type

R=ken
CC=golang-dev
https://golang.org/cl/5331043

src/cmd/gc/export.c

@@ -89,7 +89,6 @@ dumppkg(Pkg *p)
 }
 
 static void
-
 dumpexportconst(Sym *s)
 {
 	Node *n;
@@ -151,7 +150,7 @@ dumpexporttype(Type *t)
 	if(t == T)
 		return;
 
-	if(t->printed || t == types[t->etype] || t == bytetype || t == runetype)
+	if(t->printed || t == types[t->etype] || t == bytetype || t == runetype || t == errortype)
 		return;
 	t->printed = 1;
 

src/cmd/gc/fmt.c

@@ -553,6 +553,9 @@ typefmt(Fmt *fp, Type *t)
 		t = types[t->etype];
 	}
 
+	if(t == errortype)
+		return fmtstrcpy(fp, "error");
+
 	// Unless the 'l' flag was specified, if the type has a name, just print that name.
 	if(!(fp->flags&FmtLong) && t->sym && t->etype != TFIELD && t != types[t->etype]) {
 		switch(fmtmode) {

src/cmd/gc/go.h

@@ -786,6 +786,7 @@ EXTERN	Type*	idealstring;
 EXTERN	Type*	idealbool;
 EXTERN	Type*	bytetype;
 EXTERN	Type*	runetype;
+EXTERN	Type*	errortype;
 EXTERN	uchar	simtype[NTYPE];
 EXTERN	uchar	isptr[NTYPE];
 EXTERN	uchar	isforw[NTYPE];

src/cmd/gc/lex.c

@@ -1759,6 +1759,40 @@ static void
 lexinit1(void)
 {
 	Sym *s, *s1;
+	Type *t, *f, *rcvr, *in, *out;
+
+	// t = interface { Error() string }
+	rcvr = typ(TSTRUCT);
+	rcvr->type = typ(TFIELD);
+	rcvr->type->type = ptrto(typ(TSTRUCT));
+	rcvr->funarg = 1;
+	in = typ(TSTRUCT);
+	in->funarg = 1;
+	out = typ(TSTRUCT);
+	out->type = typ(TFIELD);
+	out->type->type = types[TSTRING];
+	out->funarg = 1;
+	f = typ(TFUNC);
+	*getthis(f) = rcvr;
+	*getoutarg(f) = out;
+	*getinarg(f) = in;
+	f->thistuple = 1;
+	f->intuple = 0;
+	f->outnamed = 0;
+	f->outtuple = 1;
+	t = typ(TINTER);
+	t->type = typ(TFIELD);
+	t->type->sym = lookup("Error");
+	t->type->type = f;
+
+	// error type
+	s = lookup("error");
+	s->lexical = LNAME;
+	errortype = t;
+	errortype->sym = s;
+	s1 = pkglookup("error", builtinpkg);
+	s1->lexical = LNAME;
+	s1->def = typenod(errortype);
 
 	// byte alias
 	s = lookup("byte");
@@ -1821,6 +1855,10 @@ lexfini(void)
 	if(s->def == N)
 		s->def = typenod(bytetype);
 	
+	s = lookup("error");
+	if(s->def == N)
+		s->def = typenod(errortype);
+
 	s = lookup("rune");
 	if(s->def == N)
 		s->def = typenod(runetype);

src/cmd/gc/reflect.c

@@ -693,8 +693,13 @@ dtypesym(Type *t)
 		tbase = t->type;
 	dupok = tbase->sym == S;
 
-	if(compiling_runtime && (tbase == types[tbase->etype] || tbase == bytetype || tbase == runetype))	// int, float, etc
+	if(compiling_runtime && 
+			(tbase == types[tbase->etype] ||
+			tbase == bytetype ||
+			tbase == runetype ||
+			tbase == errortype)) { // int, float, etc
 		goto ok;
+	}
 
 	// named types from other files are defined only by those files
 	if(tbase->sym && !tbase->local)
@@ -904,6 +909,13 @@ dumptypestructs(void)
 		dtypesym(ptrto(types[TSTRING]));
 		dtypesym(ptrto(types[TUNSAFEPTR]));
 
+		// emit type structs for error and func(error) string.
+		// The latter is the type of an auto-generated wrapper.
+		dtypesym(ptrto(errortype));
+		dtypesym(functype(nil, 
+			list1(nod(ODCLFIELD, N, typenod(errortype))),
+			list1(nod(ODCLFIELD, N, typenod(types[TSTRING])))));
+		
 		// add paths for runtime and main, which 6l imports implicitly.
 		dimportpath(runtimepkg);
 		dimportpath(mkpkg(strlit("main")));

src/cmd/gc/subr.c

@@ -1483,7 +1483,7 @@ ptrto(Type *t)
 	Type *t1;
 
 	if(tptr == 0)
-		fatal("ptrto: nil");
+		fatal("ptrto: no tptr");
 	t1 = typ(tptr);
 	t1->type = t;
 	t1->width = widthptr;