cgen: fix generic type $else $if (#8339)

vlib/v/ast/str.v

@@ -312,6 +312,9 @@ pub fn (x Expr) str() string {
 		StringLiteral {
 			return '"$x.val"'
 		}
+		Type {
+			return 'Type($x.typ)'
+		}
 		TypeOf {
 			return 'typeof($x.expr.str())'
 		}

vlib/v/checker/checker.v

@@ -4361,7 +4361,7 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 	mut nbranches_without_return := 0
 	mut should_skip := false // Whether the current branch should be skipped
 	mut found_branch := false // Whether a matching branch was found- skip the rest
-	mut is_comptime_t_is_expr := false // if `$if T is string`
+	mut is_comptime_type_is_expr := false // if `$if T is string`
 	for i in 0 .. node.branches.len {
 		mut branch := node.branches[i]
 		if branch.cond is ast.ParExpr {
@@ -4443,8 +4443,9 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 					got_type := (branch.cond.right as ast.Type).typ
 					if left is ast.SelectorExpr {
 						c.comptime_fields_type[left.expr.str()] = got_type
+						is_comptime_type_is_expr = true
 					} else if left is ast.Type {
-						is_comptime_t_is_expr = true
+						is_comptime_type_is_expr = true
 						left_type := c.unwrap_generic(left.typ)
 						if left_type != got_type {
 							should_skip = true
@@ -4458,12 +4459,12 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 			} else if should_skip {
 				c.skip_flags = true
 				should_skip = false // Reset the value of `should_skip` for the next branch
-			} else {
+			} else if !is_comptime_type_is_expr {
 				found_branch = true // If a branch wasn't skipped, the rest must be
 			}
 			if !c.skip_flags || c.pref.output_cross_c {
 				c.stmts(branch.stmts)
-			} else if !is_comptime_t_is_expr {
+			} else if !is_comptime_type_is_expr {
 				node.branches[i].stmts = []
 			}
 			c.skip_flags = cur_skip_flags

vlib/v/gen/comptime.v

@@ -155,13 +155,14 @@ fn (mut g Gen) comp_if(node ast.IfExpr) {
 		start_pos := g.out.len
 		if i == node.branches.len - 1 && node.has_else {
 			g.writeln('#else')
+			comp_if_stmts_skip = false
 		} else {
 			if i == 0 {
 				g.write('#if ')
 			} else {
 				g.write('#elif ')
 			}
-			g.comp_if_expr(branch.cond)
+			comp_if_stmts_skip = !g.comp_if_cond(branch.cond)
 			g.writeln('')
 		}
 		expr_str := g.out.last_n(g.out.len - start_pos).trim_space()
@@ -193,30 +194,12 @@ fn (mut g Gen) comp_if(node ast.IfExpr) {
 			if should_create_scope {
 				g.writeln('{')
 			}
-			if branch.cond is ast.InfixExpr {
-				if branch.cond.op == .key_is {
-					left := branch.cond.left
-					got_type := (branch.cond.right as ast.Type).typ
-					if left is ast.Type {
-						left_type := g.unwrap_generic(left.typ)
-						if left_type != got_type {
-							comp_if_stmts_skip = true
-						}
-					}
-				}
-			}
-			is_else := node.has_else && i == node.branches.len - 1
-			if !comp_if_stmts_skip || (comp_if_stmts_skip && is_else) {
+			if !comp_if_stmts_skip {
 				g.stmts(branch.stmts)
 			}
 			if should_create_scope {
 				g.writeln('}')
 			}
-			if !comp_if_stmts_skip && branch.cond is ast.InfixExpr {
-				if (branch.cond as ast.InfixExpr).op == .key_is {
-					break
-				}
-			}
 		}
 		g.defer_ifdef = ''
 	}
@@ -227,33 +210,37 @@ fn (mut g Gen) comp_if(node ast.IfExpr) {
 	}
 }
 
-fn (mut g Gen) comp_if_expr(cond ast.Expr) {
+fn (mut g Gen) comp_if_cond(cond ast.Expr) bool {
 	match cond {
 		ast.BoolLiteral {
 			g.expr(cond)
+			return true
 		}
 		ast.ParExpr {
 			g.write('(')
-			g.comp_if_expr(cond.expr)
+			is_cond_true := g.comp_if_cond(cond.expr)
 			g.write(')')
+			return is_cond_true
 		}
 		ast.PrefixExpr {
 			g.write(cond.op.str())
-			g.comp_if_expr(cond.right)
+			return g.comp_if_cond(cond.right)
 		}
 		ast.PostfixExpr {
 			ifdef := g.comp_if_to_ifdef((cond.expr as ast.Ident).name, true) or {
 				verror(err)
-				return
+				return false
 			}
 			g.write('defined($ifdef)')
+			return true
 		}
 		ast.InfixExpr {
 			match cond.op {
 				.and, .logical_or {
-					g.comp_if_expr(cond.left)
+					l := g.comp_if_cond(cond.left)
 					g.write(' $cond.op ')
-					g.comp_if_expr(cond.right)
+					r := g.comp_if_cond(cond.right)
+					return l && r
 				}
 				.key_is, .not_is {
 					left := cond.left
@@ -268,23 +255,34 @@ fn (mut g Gen) comp_if_expr(cond ast.Expr) {
 						// this is only allowed for generics currently, otherwise blocked by checker
 						exp_type = g.unwrap_generic(left.typ)
 					}
-					op := if cond.op == .key_is { '==' } else { '!=' }
-					g.write('$exp_type $op $got_type')
+
+					if cond.op == .key_is {
+						g.write('$exp_type == $got_type')
+						return exp_type == got_type
+					} else {
+						g.write('$exp_type !=$got_type')
+						return exp_type != got_type
+					}
 				}
 				.eq, .ne {
 					// TODO Implement `$if method.args.len == 1`
 					g.write('1')
+					return true
+				}
+				else {
+					return true
 				}
-				else {}
 			}
 		}
 		ast.Ident {
 			ifdef := g.comp_if_to_ifdef(cond.name, false) or { 'true' } // handled in checker
 			g.write('defined($ifdef)')
+			return true
 		}
 		else {
 			// should be unreachable, but just in case
 			g.write('1')
+			return true
 		}
 	}
 }

vlib/v/tests/comptime_if_expr_test.v

@@ -81,6 +81,14 @@ fn test_generic_t_is3() {
 	assert res == GenericTIsTest{}
 }
 
+fn generic_t_is_with_else<T>(raw_data string) ?T {
+	$if T is string {
+		return raw_data
+	} $else {
+		return T{}
+	}
+}
+
 fn test_generic_t_is_with_else() {
 	res := generic_t_is_with_else<GenericTIsTest>('') or {
 		assert false
@@ -94,10 +102,25 @@ fn test_generic_t_is_with_else() {
 	assert str == 'test'
 }
 
-fn generic_t_is_with_else<T>(raw_data string) ?T {
-	$if T is string {
-		return raw_data
-	} $else {
-		return T{}
+fn generic_t_is_with_else_if<T>() []string {
+	mut fields := []string{}
+	$for field in T.fields {
+		$if field.typ is string {
+			fields << field.name
+		} $else $if field.typ is int {
+			fields << field.name
+		}
 	}
+	return fields
 }
+
+struct User {
+	name string
+	age  int
+}
+
+fn test_generic_t_is_with_else_if() {
+	x := generic_t_is_with_else_if<User>()
+	assert x == ['name', 'age']
+}
+