Explorer: Support class extension (#1946)

Support class extension with `extends`
Relates to #1881 

Add support for:
* Class extension with `extends`
* Using base class methods and members

explorer/testdata/class/class_inheritance_function_call.carbon

@@ -0,0 +1,40 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// RUN: %{explorer-run}
+// RUN: %{explorer-run-trace}
+// CHECK:STDOUT: Class C, call 0
+// CHECK:STDOUT: Class D, call 0
+// CHECK:STDOUT: Class C, call 1
+// CHECK:STDOUT: Class C, call 2
+// CHECK:STDOUT: Class D, call 2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  fn FunctionC(var i: i32) {
+    Print("Class C, call {0}", i);
+  }
+}
+
+class D extends C {
+  fn FunctionD(var i: i32) {
+    C.FunctionC(i);
+    Print("Class D, call {0}", i);
+  }
+}
+
+fn Main() -> i32 {
+  // Calling function from class type
+  D.FunctionD(0);
+  // Note: D.FunctionC(0); is not accessible
+
+  // Calling function from class object
+  var d: D = {};
+  d.FunctionC(1);
+  d.FunctionD(2);
+  return 0;
+}

explorer/testdata/class/class_inheritance_methods.carbon

@@ -0,0 +1,38 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// RUN: %{explorer-run}
+// RUN: %{explorer-run-trace}
+// CHECK:STDOUT: Class 1
+// CHECK:STDOUT: Class 2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  fn BasePrint(v: i32) {
+    Print("Class {0}", v);
+  }
+  fn Method1[me:Self]() {
+    me.BasePrint(me.value_c);
+  }
+
+  var value_c: i32;
+}
+
+class D extends C {
+  fn Method2[me:Self]() {
+    me.BasePrint(me.value_d);
+  }
+
+  var value_d: i32;
+}
+
+fn Main() -> i32 {
+  var d: D = {.value_c = 1, .value_d = 2};
+  d.Method1();
+  d.Method2();
+  return 0;
+}

explorer/testdata/class/class_inheritance_multiple.carbon

@@ -0,0 +1,33 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// RUN: %{explorer-run}
+// RUN: %{explorer-run-trace}
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class A {
+  fn FunctionA() {}
+  var var_a: i32;
+}
+
+base class B extends A {
+  fn FunctionB() {}
+  var var_b: i32;
+}
+
+class C extends B {
+  fn FunctionC() {}
+  var var_c: i32;
+}
+
+fn Main() -> i32 {
+  var c: C = {.var_a=1, .var_b=2, .var_c=3};
+  c.FunctionA();
+  c.FunctionB();
+  c.FunctionC();
+  return 0;
+}

explorer/testdata/class/class_inheritance_shadow.carbon

@@ -0,0 +1,40 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// RUN: %{explorer-run}
+// RUN: %{explorer-run-trace}
+// CHECK:STDOUT: Class D
+// CHECK:STDOUT: d.value = 2
+// CHECK:STDOUT: d.GetValue() = 2
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  fn Method1() {
+    Print("Class C");
+  }
+  fn GetValue[me: Self]() -> i32 {
+    return me.value;
+  }
+  var value: i32;
+}
+
+class D extends C {
+  fn Method1() {
+    Print("Class D");
+  }
+  var value: i32;
+}
+
+fn Main() -> i32 {
+  // Initialize derived value first, base value second
+  var d: D = {.value = 2, .value = 1};
+  d.Method1();
+
+  Print("d.value = {0}", d.value);
+  Print("d.GetValue() = {0}", d.GetValue());
+  return 0;
+}

explorer/testdata/class/class_inheritance_variables.carbon

@@ -0,0 +1,39 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+// RUN: %{explorer-run}
+// RUN: %{explorer-run-trace}
+// CHECK:STDOUT: Read var_c=1
+// CHECK:STDOUT: Read var_d=2
+// CHECK:STDOUT: Assign var_c=3
+// CHECK:STDOUT: Assign var_d=4
+// CHECK:STDOUT: result: 0
+
+package ExplorerTest api;
+
+base class C {
+  var var_c: i32;
+}
+
+class D extends C {
+  var var_d: i32;
+}
+
+fn Main() -> i32 {
+  // Initialization
+  var d: D = {.var_c= 1, .var_d= 2};
+
+  // Read
+  Print("Read var_c={0}", d.var_c);
+  Print("Read var_d={0}", d.var_d);
+
+  // Assignment
+  d.var_c = 3;
+  d.var_d = 4;
+  Print("Assign var_c={0}", d.var_c);
+  Print("Assign var_d={0}", d.var_d);
+
+  return 0;
+}

explorer/testdata/class/fail_abstract_class.carbon

@@ -10,7 +10,7 @@ package ExplorerTest api;
 
 abstract class C {
   fn F() {}
-// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_abstract_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_abstract_class.carbon:[[@LINE+1]]: Class prefix `abstract` is not supported yet
 }
 
 fn Main() -> i32 {

explorer/testdata/class/fail_extends_final_class.carbon

@@ -8,13 +8,13 @@
 
 package ExplorerTest api;
 
-class A {
+class C {
   fn F() {}
 }
 
-class B extends A {
-  fn F() {}
-// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_class_extends.carbon:[[@LINE+1]]: Class extension with `extends` is not supported yet
+class D extends C {
+  fn G() {}
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_extends_final_class.carbon:[[@LINE+1]]: Base class `C` is `final` and cannot inherited. Add the `base` or `abstract` class prefix to `C` to allow it to be inherited
 }
 
 fn Main() -> i32 {

explorer/testdata/class/fail_extends_non_class.carbon

@@ -8,9 +8,10 @@
 
 package ExplorerTest api;
 
-base class C {
-  fn F() {}
-// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_base_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_extends_non_class.carbon:[[@LINE+1]]: Expected a type, but got 3
+class C extends 3 {
+  var x: i32;
+  var y: i32;
 }
 
 fn Main() -> i32 {