checker: add error for `if c >= A && c <= Z {` in non generic functions

vlib/v/checker/checker.v

@@ -89,6 +89,7 @@ pub mut:
 	inside_defer              bool // true inside `defer {}` blocks
 	inside_fn_arg             bool // `a`, `b` in `a.f(b)`
 	inside_ct_attr            bool // true inside `[if expr]`
+	inside_x_is_type          bool // true inside the Type expression of `if x is Type {`
 	inside_comptime_for_field bool
 	skip_flags                bool      // should `#flag` and `#include` be skipped
 	fn_level                  int       // 0 for the top level, 1 for `fn abc() {}`, 2 for a nested fn, etc
@@ -156,6 +157,7 @@ fn (mut c Checker) reset_checker_state_at_start_of_new_file() {
 	c.inside_defer = false
 	c.inside_fn_arg = false
 	c.inside_ct_attr = false
+	c.inside_x_is_type = false
 	c.skip_flags = false
 	c.fn_level = 0
 	c.expr_level = 0
@@ -1605,9 +1607,10 @@ fn (mut c Checker) assert_stmt(node ast.AssertStmt) {
 
 fn (mut c Checker) block(node ast.Block) {
 	if node.is_unsafe {
+		prev_unsafe := c.inside_unsafe
 		c.inside_unsafe = true
 		c.stmts(node.stmts)
-		c.inside_unsafe = false
+		c.inside_unsafe = prev_unsafe
 	} else {
 		c.stmts(node.stmts)
 	}
@@ -2021,7 +2024,9 @@ pub fn (mut c Checker) expr(node_ ast.Expr) ast.Type {
 			c.error('incorrect use of compile-time type', node.pos)
 		}
 		ast.EmptyExpr {
+			print_backtrace()
 			c.error('checker.expr(): unhandled EmptyExpr', token.Pos{})
+			return ast.void_type
 		}
 		ast.CTempVar {
 			return node.typ
@@ -2269,6 +2274,11 @@ pub fn (mut c Checker) expr(node_ ast.Expr) ast.Type {
 			return c.struct_init(mut node)
 		}
 		ast.TypeNode {
+			if !c.inside_x_is_type && node.typ.has_flag(.generic) && unsafe { c.table.cur_fn != 0 }
+				&& c.table.cur_fn.generic_names.len == 0 {
+				c.error('unexpected generic variable in non-generic function `$c.table.cur_fn.name`',
+					node.pos)
+			}
 			return node.typ
 		}
 		ast.TypeOf {

vlib/v/checker/comptime.v

@@ -9,7 +9,9 @@ import v.util
 import v.pkgconfig
 
 fn (mut c Checker) comptime_call(mut node ast.ComptimeCall) ast.Type {
+	if node.left !is ast.EmptyExpr {
 		node.left_type = c.expr(node.left)
+	}
 	if node.method_name == 'compile_error' {
 		c.error(node.args_var, node.pos)
 		return ast.void_type

vlib/v/checker/for.v

@@ -165,10 +165,13 @@ fn (mut c Checker) for_stmt(mut node ast.ForStmt) {
 	c.in_for_count++
 	prev_loop_label := c.loop_label
 	c.expected_type = ast.bool_type
+	if node.cond !is ast.EmptyExpr {
 		typ := c.expr(node.cond)
-	if !node.is_inf && typ.idx() != ast.bool_type_idx && !c.pref.translated && !c.file.is_translated {
+		if !node.is_inf && typ.idx() != ast.bool_type_idx && !c.pref.translated
+			&& !c.file.is_translated {
 			c.error('non-bool used as for condition', node.pos)
 		}
+	}
 	if mut node.cond is ast.InfixExpr {
 		if node.cond.op == .key_is {
 			if node.cond.right is ast.TypeNode && node.cond.left in [ast.Ident, ast.SelectorExpr] {

vlib/v/checker/infix.v

@@ -12,7 +12,14 @@ pub fn (mut c Checker) infix_expr(mut node ast.InfixExpr) ast.Type {
 	mut left_type := c.expr(node.left)
 	node.left_type = left_type
 	c.expected_type = left_type
+
+	if node.op == .key_is {
+		c.inside_x_is_type = true
+	}
 	mut right_type := c.expr(node.right)
+	if node.op == .key_is {
+		c.inside_x_is_type = false
+	}
 	node.right_type = right_type
 	if left_type.is_number() && !left_type.is_ptr()
 		&& right_type in [ast.int_literal_type, ast.float_literal_type] {

vlib/v/checker/tests/generic_type_name_in_non_generic_function.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/generic_type_name_in_non_generic_function.vv:3:10: error: unexpected generic variable in non-generic function `main`
+    1 | fn main() {
+    2 |     c := u8(`D`)
+    3 |     if c >= A && c <= Z {
+      |             ^
+    4 |         println('yes')
+    5 |     } else {

vlib/v/checker/tests/generic_type_name_in_non_generic_function.vv

@@ -0,0 +1,8 @@
+fn main() {
+	c := u8(`D`)
+	if c >= A && c <= Z {
+		println('yes')
+	} else {
+		println('no')
+	}
+}

vlib/vweb/vweb.v

@@ -252,7 +252,7 @@ pub fn (mut ctx Context) file(f_path string) Result {
 		return Result{}
 	}
 	content_type := vweb.mime_types[ext]
-	if content_type.len == O {
+	if content_type.len == 0 {
 		eprintln('no MIME type found for extension $ext')
 		ctx.server_error(500)
 	} else {