os.read_file(): replace C code with V, return `?string`, handle errors

everywhere

compiler/main.v

@@ -762,13 +762,19 @@ fn new_v(args[]string) *V {
 	// Location of all vlib files
 	mut lang_dir = ''
 	// First try fetching it from VROOT if it's defined
+	for { // TODO tmp hack for optionals
 	vroot_path := TmpPath + '/VROOT'
 	if os.file_exists(vroot_path) {
-		vroot := os.read_file(vroot_path).trim_space()
+		mut vroot := os.read_file(vroot_path) or {
+			break
+		}
+		vroot=vroot.trim_space() 
 		if os.dir_exists(vroot) && os.dir_exists(vroot + '/builtin') {
 			lang_dir = vroot
 		}
 	}
+	break
+	}
 	// no "~/.vlang/VROOT" file, so the user must be running V for the first 
 	// time.
 	if lang_dir == ''  {

compiler/scanner.v

@@ -32,9 +32,13 @@ fn new_scanner(file_path string) *Scanner {
 	if !os.file_exists(file_path) {
 		panic('"$file_path" doesn\'t exist')
 	}
+	text := os.read_file(file_path) or {
+		panic('scanner: failed to open "$file_path"')
+		return &Scanner{}
+	}
 	scanner := &Scanner {
 		file_path: file_path
-		text: os.read_file(file_path)
+		text: text
 		fmt_out: new_string_builder(1000)
 	}
 	// println('new scanner "$file_path" txt.len=$scanner.text.len')

os/os.v

@@ -41,22 +41,25 @@ fn parse_windows_cmd_line(cmd byteptr) {
 	# os__args = vals;
 }
 
+fn C.ftell(fp voidptr) int
+
 // read_file reads the file in `path` and returns the contents.
-// TODO return `?string`
-pub fn read_file(path string) string {
-	res := ''
-	# FILE *f = fopen(path.str, "r");
-	# if (!f) return tos("", 0);
-	# fseek(f, 0, SEEK_END);
-	# long fsize = ftell(f);
-	// # fseek(f, 0, SEEK_SET);  //same as rewind(f);
-	# rewind(f);
-	# char *string = malloc(fsize + 1);
-	# fread(string, fsize, 1, f);
-	# fclose(f);
-	# string[fsize] = 0;
-	// # printf("RFILE= %s\n", string);
-	# res = tos(string, fsize);
+pub fn read_file(path string) ?string {
+	mut res := ''
+	cpath := path.cstr()
+	fp := C.fopen(cpath, 'r')
+	if isnil(fp) {
+		return error('failed to open file "$path"')
+	}
+	C.fseek(fp, 0, SEEK_END)
+	fsize := C.ftell(fp)
+	// C.fseek(fp, 0, SEEK_SET)  // same as C.rewind(fp) below
+	C.rewind(fp)
+	mut str := malloc(fsize + 1)
+	C.fread(str, fsize, 1, fp)
+	C.fclose(fp)
+	str[fsize] = 0
+	res = tos(str, fsize)
 	return res
 }