eliminate package global name space

R=ken2
CC=golang-dev
https://golang.org/cl/194071

src/cmd/gc/go.y

@@ -237,14 +237,13 @@ import_package:
 		importpkg->name = $2->name;
 		importpkg->direct = 1;
 
-		// PGNS: fixme
+		// NOTE(rsc): This is no longer a technical restriction:
+		// the 6g tool chain would work just fine without giving
+		// special meaning to a package being named main.
+		// Other implementations might need the restriction
+		// (gccgo does), so it stays in the language and the compiler.
 		if(strcmp($2->name, "main") == 0)
 			yyerror("cannot import package main");
-
-		// PGNS: This should go away once we get
-		// rid of the global package name space.
-		if(localpkg->name && strcmp($2->name, localpkg->name) == 0 && !compiling_runtime)
-			yyerror("package cannot import itself");
 	}
 
 import_there:

src/cmd/gc/lex.c

@@ -285,9 +285,7 @@ importfile(Val *f, int line)
 	Strlit *path;
 	char cleanbuf[1024];
 
-	// TODO(rsc): don't bother reloading imports more than once
-
-	// PGNS: canonicalize import path for ./ imports in findpkg.
+	// TODO(rsc): don't bother reloading imports more than once?
 
 	if(f->ctype != CTSTR) {
 		yyerror("import statement not a string");

src/cmd/ld/go.c

@@ -73,7 +73,7 @@ static int parsepkgdata(char*, char*, char**, char*, char**, char**, char**);
 void
 ldpkg(Biobuf *f, char *pkg, int64 len, char *filename)
 {
-	char *data, *p0, *p1;
+	char *data, *p0, *p1, *name;
 
 	if(debug['g'])
 		return;
@@ -111,10 +111,18 @@ ldpkg(Biobuf *f, char *pkg, int64 len, char *filename)
 			return;
 		}
 		p0 += 8;
-		while(*p0 == ' ' || *p0 == '\t' || *p0 == '\n')
+		while(p0 < p1 && *p0 == ' ' || *p0 == '\t' || *p0 == '\n')
 			p0++;
-		while(*p0 != ' ' && *p0 != '\t' && *p0 != '\n')
+		name = p0;
+		while(p0 < p1 && *p0 != ' ' && *p0 != '\t' && *p0 != '\n')
 			p0++;
+		if(p0 < p1) {
+			*p0++ = '\0';
+			if(strcmp(pkg, "main") == 0 && strcmp(name, "main") != 0)
+				fprint(2, "%s: %s: not package main (package %s)\n", argv0, filename, name);
+			else if(strcmp(pkg, "main") != 0 && strcmp(name, "main") == 0)
+				fprint(2, "%s: %s: importing %s, found package main", argv0, filename, pkg);
+		}
 		loadpkgdata(filename, pkg, p0, p1 - p0);
 	}
 
@@ -131,7 +139,6 @@ ldpkg(Biobuf *f, char *pkg, int64 len, char *filename)
 		return;
 	}
 
-	// PGNS: Should be using import path, not pkg.
 	loadpkgdata(filename, pkg, p0, p1 - p0);
 
 	// look for dynld section