build: separate package identity from storage paths

cmd/w6c/main.c

@@ -22,6 +22,18 @@ slurp(const char *path, char **outbuf, u64 *outlen)
 	return 0;
 }
 
+static int
+export_owner_matches(const char *buf, u64 len, const char *path)
+{
+	static const char prefix[] = "//ww:module ";
+	size_t pn = strlen(path);
+	size_t need = sizeof prefix - 1 + pn + 1;
+	return len >= need
+	    && memcmp(buf, prefix, sizeof prefix - 1) == 0
+	    && memcmp(buf + sizeof prefix - 1, path, pn) == 0
+	    && buf[need - 1] == '\n';
+}
+
 struct importin {
 	const char *path;
 	const char *file;
@@ -164,6 +176,13 @@ main(int argc, char **argv)
 			    imports[i].path, imports[i].file);
 			return 1;
 		}
+		if (!export_owner_matches(imports[i].buf, imports[i].len,
+		    imports[i].path)) {
+			fprintf(stderr,
+			    "w6c: import %s: export owner mismatch in %s\n",
+			    imports[i].path, imports[i].file);
+			return 1;
+		}
 		int bad = 0;
 		Node *f = parseinput(a, imports[i].file, imports[i].buf,
 		    imports[i].len, imports[i].path, testsupport, 0, &bad);