parser: check for import errors

vlib/v/checker/tests/import_multiple_modules_err.out

@@ -0,0 +1,5 @@
+vlib/v/checker/tests/import_multiple_modules_err.v:1:13: error: cannot import multiple modules at a time
+    1 | import time math
+      |             ~~~~
+    2 | fn main() {
+    3 |     println(time.now().unix_time())

vlib/v/checker/tests/import_multiple_modules_err.vv

@@ -0,0 +1,4 @@
+import time math
+fn main() {
+	println(time.now().unix_time())
+}

vlib/v/checker/tests/import_not_same_line_err.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/import_not_same_line_err.v:2:2: error: `import` and `module` must be at same line
+    1 | import
+    2 |  time
+      |  ~~~~
+    3 | fn main() {
+    4 |     println(time.now())

vlib/v/checker/tests/import_not_same_line_err.vv

@@ -0,0 +1,5 @@
+import
+ time
+fn main() {
+	println(time.now())
+}

vlib/v/checker/tests/import_syntax_err.out

@@ -0,0 +1,5 @@
+vlib/v/checker/tests/import_syntax_err.v:1:12: error: module syntax error, please use `x.y.z`
+    1 | import time, os
+      |            ^
+    2 | fn main() {
+    3 |     println(time.now())

vlib/v/checker/tests/import_syntax_err.vv

@@ -0,0 +1,4 @@
+import time, os
+fn main() {
+	println(time.now())
+}

vlib/v/parser/parser.v

@@ -958,15 +958,26 @@ fn (mut p Parser) module_decl() ast.Module {
 }
 
 fn (mut p Parser) import_stmt() ast.Import {
+	import_pos := p.tok.position()
 	p.check(.key_import)
 	pos := p.tok.position()
 	if p.tok.kind == .lpar {
 		p.error_with_pos('`import()` has been deprecated, use `import x` instead', pos)
 	}
 	mut mod_name := p.check_name()
+	if import_pos.line_nr != pos.line_nr {
+		p.error_with_pos('`import` and `module` must be at same line', pos)
+	}
 	mut mod_alias := mod_name
 	for p.tok.kind == .dot {
 		p.next()
+		pos_t := p.tok.position()
+		if p.tok.kind != .name {
+			p.error_with_pos('module syntax error, please use `x.y.z`', pos)
+		}
+		if import_pos.line_nr != pos_t.line_nr {
+			p.error_with_pos('`import` and `submodule` must be at same line', pos)
+		}
 		submod_name := p.check_name()
 		mod_name += '.' + submod_name
 		mod_alias = submod_name
@@ -975,6 +986,14 @@ fn (mut p Parser) import_stmt() ast.Import {
 		p.next()
 		mod_alias = p.check_name()
 	}
+	pos_t := p.tok.position()
+	if import_pos.line_nr == pos_t.line_nr {
+		if p.tok.kind != .name {
+			p.error_with_pos('module syntax error, please use `x.y.z`', pos_t)
+		} else {
+			p.error_with_pos('cannot import multiple modules at a time', pos_t)
+		}
+	}
 	p.imports[mod_alias] = mod_name
 	p.table.imports << mod_name
 	node := ast.Import{