checker: fix comptime if branch checking (#16938)

vlib/v/checker/if.v

@@ -131,8 +131,9 @@ fn (mut c Checker) if_expr(mut node ast.IfExpr) ast.Type {
 			} else if skip_state == .skip {
 				c.skip_flags = true
 				skip_state = .unknown // Reset the value of `skip_state` for the next branch
-			} else if !is_comptime_type_is_expr && skip_state == .eval {
+			} else if skip_state == .eval {
 				found_branch = true // If a branch wasn't skipped, the rest must be
+				c.skip_flags = skip_state == .skip
 			}
 			if c.fn_level == 0 && c.pref.output_cross_c {
 				// do not skip any of the branches for top level `$if OS {`

vlib/v/checker/return.v

@@ -270,7 +270,9 @@ fn has_top_return(stmts []ast.Stmt) bool {
 			}
 			ast.ExprStmt {
 				if stmt.expr is ast.CallExpr {
-					if stmt.expr.is_noreturn {
+					// do not ignore panic() calls on non checked stmts
+					if stmt.expr.is_noreturn
+						|| (stmt.expr.is_method == false && stmt.expr.name == 'panic') {
 						return true
 					}
 				}

vlib/v/checker/tests/comptime_branching_working_with_a_custom_compile_error.out

@@ -0,0 +1,7 @@
+vlib/v/checker/tests/comptime_branching_working_with_a_custom_compile_error.vv:8:3: error: 11
+    6 |         return Value(val)
+    7 |     } $else {
+    8 |         $compile_error('11')
+      |         ~~~~~~~~~~~~~~~~~~~~
+    9 |         println('not bool ${val}')
+   10 |     }

vlib/v/checker/tests/comptime_branching_working_with_a_custom_compile_error.vv

@@ -0,0 +1,16 @@
+type Value = bool | voidptr
+
+pub fn create[T](val T) Value {
+	$if T is bool {
+		println('bool ${val}')
+		return Value(val)
+	} $else {
+		$compile_error('11')
+		println('not bool ${val}')
+	}
+	return Value(voidptr(123))
+}
+
+fn main() {
+	println(create(123))
+}

vlib/v/tests/comptime_branching_working_without_compile_error_test.v

@@ -0,0 +1,16 @@
+type Value = bool | voidptr
+
+pub fn create[T](val T) Value {
+	$if T is bool {
+		println('bool ${val}')
+		return Value(val)
+	} $else {
+		$compile_error('11')
+		println('not bool ${val}')
+	}
+	return Value(voidptr(123))
+}
+
+fn test_calling_generic_function_that_has_inside_a_comptime_compile_error_directive() {
+	assert create(true) == Value(true)
+}