parser: improve syntax errors in module declarations

vlib/v/checker/tests/module_multiple_names_err.out

@@ -1,5 +0,0 @@
-vlib/v/checker/tests/module_multiple_names_err.vv:1:13: error: `module x` can only declare one module
-    1 | module main os
-      |             ~~
-    2 | fn main() {
-    3 |     println('hello, world')

vlib/v/checker/tests/module_syntax_err.out

@@ -1,5 +0,0 @@
-vlib/v/checker/tests/module_syntax_err.vv:1:12: error: `module x` syntax error
-    1 | module main.os
-      |            ^
-    2 | fn main() {
-    3 |     println('hello, world')

vlib/v/parser/parser.v

@@ -1835,12 +1835,14 @@ fn (mut p Parser) module_decl() ast.Module {
 		// as it creates a wrong position when extended
 		// to module_pos
 		n_pos := p.tok.position()
-		if module_pos.line_nr == n_pos.line_nr && p.tok.kind != .comment {
-			if p.tok.kind != .name {
-				p.error_with_pos('`module x` syntax error', n_pos)
+		if module_pos.line_nr == n_pos.line_nr && p.tok.kind != .comment && p.tok.kind != .eof {
+			if p.tok.kind == .name {
+				p.error_with_pos('`module $name`, you can only declare one module, unexpected `$p.tok.lit`',
+					n_pos)
 				return mod_node
 			} else {
-				p.error_with_pos('`module x` can only declare one module', n_pos)
+				p.error_with_pos('`module $name`, unexpected `$p.tok.kind` after module name',
+					n_pos)
 				return mod_node
 			}
 		}

vlib/v/parser/tests/module_multiple_names_err.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/module_multiple_names_err.vv:1:13: error: `module main`, you can only declare one module, unexpected `os`
+    1 | module main os
+      |             ~~
+    2 | fn main() {
+    3 |     println('hello, world')

vlib/v/parser/tests/module_syntax_err.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/module_syntax_err.vv:1:12: error: `module main`, unexpected `.` after module name
+    1 | module main.os
+      |            ^
+    2 | fn main() {
+    3 |     println('hello, world')