better handling of mistaken top-level variable

references during the parsing of :=.  the base
problem is that when reading

	a,b,c,d

the parser makes those refer to existing variables,
which might create a few stub top-level ones
for undefined names, but then if a := is the next
token, we need to undo those stubs.

this was causing problems in multifile packages
in which one file used a := variable named rpc
and the other imported a package named rpc.

R=ken
OCL=35446
CL=35446

src/cmd/gc/dcl.c

@@ -463,9 +463,15 @@ oldname(Sym *s)
 		n->op = ONONAME;
 		s->def = n;
 	}
+	if(n->oldref < 100)
+		n->oldref++;
 	if(n->funcdepth > 0 && n->funcdepth != funcdepth && n->op == ONAME) {
-		// inner func is referring to var
-		// in outer func.
+		// inner func is referring to var in outer func.
+		//
+		// TODO(rsc): If there is an outer variable x and we
+		// are parsing x := 5 inside the closure, until we get to
+		// the := it looks like a reference to the outer x so we'll
+		// make x a closure variable unnecessarily.
 		if(n->closure == N || n->closure->funcdepth != funcdepth) {
 			// create new closure var.
 			c = nod(ONAME, N, N);
@@ -554,6 +560,12 @@ colasdefn(NodeList *left, Node *defn)
 		}
 		if(n->sym->block == block)
 			continue;
+
+		// If we created an ONONAME just for this :=,
+		// delete it, to avoid confusion with top-level imports.
+		if(n->op == ONONAME && n->oldref < 100 && --n->oldref == 0)
+			n->sym->def = N;
+
 		nnew++;
 		n = newname(n->sym);
 		declare(n, dclcontext);

src/cmd/gc/go.h

@@ -202,6 +202,7 @@ struct	Node
 	uchar	initorder;
 	uchar	dodata;		// compile literal assignment as data statement
 	uchar	used;
+	uchar	oldref;
 
 	// most nodes
 	Node*	left;
@@ -247,7 +248,6 @@ struct	Node
 	Node*	outer;	// outer PPARAMREF in nested closure
 	Node*	closure;	// ONAME/PHEAP <-> ONAME/PPARAMREF
 
-	char*	pline;
 	Sym*	sym;		// various
 	int32	vargen;		// unique name for OTYPE/ONAME
 	int32	lineno;
@@ -696,8 +696,6 @@ EXTERN	int	noargnames;
 EXTERN	int	funcdepth;
 EXTERN	int	typecheckok;
 
-EXTERN	char*	importline;
-
 /*
  *	y.tab.c
  */

src/cmd/gc/go.y

@@ -178,7 +178,6 @@ import_stmt:
 		pack = nod(OPACK, N, N);
 		pack->sym = import;
 		pack->lineno = $1;
-		pack->pline = importline;
 
 		if(my == S)
 			my = import;
@@ -189,15 +188,10 @@ import_stmt:
 		if(my->name[0] == '_' && my->name[1] == '\0')
 			break;
 
-		// TODO(rsc): this line is needed for a package
-		// which does bytes := in a function, which creates
-		// an ONONAME for bytes, but then a different file
-		// imports "bytes".  more generally we need to figure out
-		// what it means if one file imports "bytes" and another
-		// declares a top-level name.
-		if(my->def && my->def->op == ONONAME)
-			my->def = N;
-
+		if(my->def) {
+			lineno = $1;
+			redeclare(my, "as imported package name");
+		}
 		my->def = pack;
 		my->lastlineno = $1;
 		import->block = 1;	// at top level
@@ -223,8 +217,6 @@ import_here:
 		$$ = parserline();
 		pkgimportname = S;
 		pkgmyname = $1;
-		if($1->def && ($1->name[0] != '_' || $1->name[1] != '\0'))
-			redeclare($1, "as imported package name");
 		importfile(&$2, $$);
 	}
 |	'.' LLITERAL

src/cmd/gc/lex.c

@@ -267,13 +267,7 @@ importfile(Val *f, int line)
 	int32 c;
 	int len;
 
-	// Once we push the new file, we will not be able
-	// to print the current lineno correctly with %L.
-	// In case that line is the line of the import (likely),
-	// save the text for use in error messages.
-	importline = smprint("%L", line);
-
-// TODO: don't bother reloading imports more than once
+	// TODO(rsc): don't bother reloading imports more than once
 
 	if(f->ctype != CTSTR) {
 		yyerror("import statement not a string");
@@ -300,12 +294,10 @@ importfile(Val *f, int line)
 		// assume .a files move (get installed)
 		// so don't record the full path.
 		p = file + len - f->u.sval->len - 2;
-		linehist(p, 0, 0);
 		linehist(p, -1, 1);	// acts as #pragma lib
 	} else {
 		// assume .6 files don't move around
 		// so do record the full path
-		linehist(file, 0, 0);
 		linehist(file, -1, 0);
 	}
 
@@ -339,8 +331,6 @@ importfile(Val *f, int line)
 void
 unimportfile(void)
 {
-	linehist(nil, 0, 0);
-
 	if(curio.bin != nil) {
 		Bterm(curio.bin);
 		curio.bin = nil;
@@ -357,7 +347,6 @@ void
 cannedimports(char *file, char *cp)
 {
 	lexlineno++;		// if sys.6 is included on line 1,
-	linehist(file, 0, 0);	// the debugger gets confused
 
 	pushedio = curio;
 	curio.bin = nil;
@@ -1018,7 +1007,7 @@ getc(void)
 	if(c != 0) {
 		curio.peekc = curio.peekc1;
 		curio.peekc1 = 0;
-		if(c == '\n')
+		if(c == '\n' && pushedio.bin == nil)
 			lexlineno++;
 		return c;
 	}
@@ -1038,7 +1027,8 @@ getc(void)
 		return EOF;
 
 	case '\n':
-		lexlineno++;
+		if(pushedio.bin == nil)
+			lexlineno++;
 		break;
 	}
 	return c;
@@ -1049,7 +1039,7 @@ ungetc(int c)
 {
 	curio.peekc1 = curio.peekc;
 	curio.peekc = c;
-	if(c == '\n')
+	if(c == '\n' && pushedio.bin == nil)
 		lexlineno--;
 }
 
@@ -1487,7 +1477,7 @@ mkpackage(char* pkg)
 					// name, so that the name cannot be redeclared
 					// as a non-package in other files.
 					if(!s->def->used) {
-						print("%s: imported and not used: %s\n", s->def->pline, s->def->sym->name);
+						print("%L: imported and not used: %s\n", s->def->lineno, s->def->sym->name);
 						nerrors++;
 					}
 					s->def = N;
@@ -1497,7 +1487,7 @@ mkpackage(char* pkg)
 					// throw away top-level name left over
 					// from previous import . "x"
 					if(s->def->pack != N && !s->def->pack->used) {
-						print("%s: imported and not used: %s\n", s->def->pack->pline, s->def->pack->sym->name);
+						print("%L: imported and not used: %s\n", s->def->pack->lineno, s->def->pack->sym->name);
 						nerrors++;
 						s->def->pack->used = 1;
 					}

src/cmd/gc/subr.c

@@ -269,7 +269,7 @@ importdot(Sym *opkg, Node *pack)
 	}
 	if(n == 0) {
 		// can't possibly be used - there were no symbols
-		print("%L: imported and not used: %s\n", pack->pline, pack->sym->name);
+		print("%L: imported and not used: %s\n", pack->lineno, pack->sym->name);
 		nerrors++;
 	}
 }