check for unused imports

R=ken
OCL=34732
CL=34756

src/cmd/gc/go.h

@@ -236,6 +236,7 @@ struct	Node
 	// ONAME
 	Node*	ntype;
 	Node*	defn;
+	Node*	pack;	// real package for import . names
 
 	// ONAME func param with PHEAP
 	Node*	heapaddr;	// temp holding heap address of param
@@ -246,7 +247,7 @@ struct	Node
 	Node*	outer;	// outer PPARAMREF in nested closure
 	Node*	closure;	// ONAME/PHEAP <-> ONAME/PPARAMREF
 
-	Sym*	psym;		// import
+	char*	pline;
 	Sym*	sym;		// various
 	int32	vargen;		// unique name for OTYPE/ONAME
 	int32	lineno;
@@ -694,6 +695,7 @@ EXTERN	int	noargnames;
 EXTERN	int	funcdepth;
 EXTERN	int	typecheckok;
 
+EXTERN	char*	importline;
 
 /*
  *	y.tab.c
@@ -704,7 +706,7 @@ int	yyparse(void);
  *	lex.c
  */
 void	addidir(char*);
-void	importfile(Val*);
+void	importfile(Val*, int line);
 void	cannedimports(char*, char*);
 void	unimportfile();
 int32	yylex(void);
@@ -788,7 +790,7 @@ uint32	stringhash(char*);
 Sym*	lookup(char*);
 Sym*	pkglookup(char*, char*);
 Sym*	restrictlookup(char*, char*);
-void	importdot(Sym*);
+void	importdot(Sym*, Node*);
 void	yyerror(char*, ...);
 int	parserline(void);
 void	warn(char*, ...);

src/cmd/gc/go.y

@@ -165,6 +165,7 @@ import_stmt:
 	import_here import_package import_there
 	{
 		Sym *import, *my;
+		Node *pack;
 
 		import = pkgimportname;
 		my = pkgmyname;
@@ -173,10 +174,16 @@ import_stmt:
 
 		if(import == S)
 			break;
+
+		pack = nod(OPACK, N, N);
+		pack->sym = import;
+		pack->lineno = $1;
+		pack->pline = importline;
+
 		if(my == S)
 			my = import;
 		if(my->name[0] == '.') {
-			importdot(import);
+			importdot(import, pack);
 			break;
 		}
 		if(my->name[0] == '_' && my->name[1] == '\0')
@@ -191,8 +198,7 @@ import_stmt:
 		if(my->def && my->def->op == ONONAME)
 			my->def = N;
 
-		my->def = nod(OPACK, N, N);
-		my->def->sym = import;
+		my->def = pack;
 		my->lastlineno = $1;
 		import->block = 1;	// at top level
 	}
@@ -209,7 +215,7 @@ import_here:
 		$$ = parserline();
 		pkgimportname = S;
 		pkgmyname = S;
-		importfile(&$1);
+		importfile(&$1, $$);
 	}
 |	sym LLITERAL
 	{
@@ -219,14 +225,14 @@ import_here:
 		pkgmyname = $1;
 		if($1->def && ($1->name[0] != '_' || $1->name[1] != '\0'))
 			redeclare($1, "as imported package name");
-		importfile(&$2);
+		importfile(&$2, $$);
 	}
 |	'.' LLITERAL
 	{
 		// import into my name space
 		$$ = parserline();
 		pkgmyname = lookup(".");
-		importfile(&$2);
+		importfile(&$2, $$);
 	}
 
 import_package:
@@ -811,6 +817,7 @@ pexpr:
 		if($1->op == OPACK) {
 			Sym *s;
 			s = restrictlookup($3->name, $1->sym->name);
+			$1->used = 1;
 			$$ = oldname(s);
 			break;
 		}
@@ -910,6 +917,8 @@ name:
 	sym
 	{
 		$$ = oldname($1);
+		if($$->pack != N)
+			$$->pack->used = 1;
 	}
 
 labelname:
@@ -995,6 +1004,7 @@ dotname:
 		if($1->op == OPACK) {
 			Sym *s;
 			s = restrictlookup($3->name, $1->sym->name);
+			$1->used = 1;
 			$$ = oldname(s);
 			break;
 		}
@@ -1245,6 +1255,14 @@ structdcl:
 
 packname:
 	LNAME
+	{
+		Node *n;
+
+		$$ = $1;
+		n = oldname($1);
+		if(n->pack != N)
+			n->pack->used = 1;
+	}
 |	LNAME '.' sym
 	{
 		char *pkg;
@@ -1252,8 +1270,10 @@ packname:
 		if($1->def == N || $1->def->op != OPACK) {
 			yyerror("%S is not a package", $1);
 			pkg = $1->name;
-		} else
+		} else {
+			$1->def->used = 1;
 			pkg = $1->def->sym->name;
+		}
 		$$ = restrictlookup($3->name, pkg);
 	}
 

src/cmd/gc/lex.c

@@ -97,6 +97,7 @@ main(int argc, char *argv[])
 			Bterm(curio.bin);
 	}
 	testdclstack();
+	mkpackage(package);	// final import not used checks
 	lexfini();
 
 	typecheckok = 1;
@@ -259,13 +260,19 @@ findpkg(Strlit *name)
 }
 
 void
-importfile(Val *f)
+importfile(Val *f, int line)
 {
 	Biobuf *imp;
 	char *file, *p;
 	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
 
 	if(f->ctype != CTSTR) {
@@ -339,6 +346,7 @@ unimportfile(void)
 		curio.bin = nil;
 	} else
 		lexlineno--;	// re correct sys.6 line number
+
 	curio = pushedio;
 	pushedio.bin = nil;
 	inimportsys = 0;
@@ -1302,7 +1310,7 @@ lexinit(void)
 	s->def = nod(ONONAME, N, N);
 	s->def->iota = 1;
 	s->def->sym = s;
-	
+
 	s = pkglookup("true", "/builtin/");
 	s->def = nodbool(1);
 	s->def->sym = lookup("true");
@@ -1453,10 +1461,10 @@ mkpackage(char* pkg)
 	int32 h;
 	char *p;
 
-	if(strcmp(pkg, "_") == 0)
-		yyerror("invalid package name _");
-
 	if(package == nopackage) {
+		if(strcmp(pkg, "_") == 0)
+			yyerror("invalid package name _");
+
 		// redefine all names to be this package.
 		for(h=0; h<NHASH; h++)
 			for(s = hash[h]; s != S; s = s->link)
@@ -1476,12 +1484,21 @@ mkpackage(char* pkg)
 					// TODO(rsc): remember that there was a package
 					// 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);
+						nerrors++;
+					}
 					s->def = N;
 					continue;
 				}
 				if(s->def->sym != s) {
 					// 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);
+						nerrors++;
+						s->def->pack->used = 1;
+					}
 					s->def = N;
 					continue;
 				}
@@ -1489,14 +1506,6 @@ mkpackage(char* pkg)
 		}
 	}
 
-/*
-	// declare this name as a package
-	s = lookup(package);
-	s->def = nod(OPACK, N, N);
-	s->def->sym = s;
-	s->block = -1;	// above top level
-*/
-
 	if(outfile == nil) {
 		p = strrchr(infile, '/');
 		if(p == nil)

src/cmd/gc/subr.c

@@ -238,15 +238,16 @@ restrictlookup(char *name, char *pkg)
 // find all the exported symbols in package opkg
 // and make them available in the current package
 void
-importdot(Sym *opkg)
+importdot(Sym *opkg, Node *pack)
 {
 	Sym *s, *s1;
 	uint32 h;
-	int c;
+	int c, n;
 
 	if(strcmp(opkg->name, package) == 0)
 		return;
 
+	n = 0;
 	c = opkg->name[0];
 	for(h=0; h<NHASH; h++) {
 		for(s = hash[h]; s != S; s = s->link) {
@@ -262,8 +263,15 @@ importdot(Sym *opkg)
 				continue;
 			}
 			s1->def = s->def;
+			s1->def->pack = pack;
+			n++;
 		}
 	}
+	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);
+		nerrors++;
+	}
 }
 
 void