feat: replace new keyword with this constructor syntax and ClassName.new() calls across core library and docs

Replace all uses of the `new` reserved word with explicit `this new()` constructor definitions and `ClassName.new()` instantiation calls in builtin/core.wren. Update all documentation files (classes.markdown, fiber.markdown, fn.markdown, sequence.markdown, error-handling.markdown, expressions.markdown, fibers.markdown, functions.markdown) to reflect the new constructor syntax, removing `new` keyword examples and replacing them with `ClassName.new()` patterns and `this new()` definitions.

test/language/constructor/cannot_be_infix.wren

@@ -0,0 +1,5 @@
+class Foo {
+  this +(value) { // expect error
+    IO.print("ok")
+  }
+}

test/language/constructor/cannot_be_minus.wren

@@ -0,0 +1,5 @@
+class Foo {
+  this -(value) { // expect error
+    IO.print("ok")
+  }
+}

test/language/constructor/cannot_be_setter.wren

@@ -0,0 +1,5 @@
+class Foo {
+  this name=(value) { // expect error
+    IO.print("ok")
+  }
+}

test/language/constructor/cannot_be_static.wren

@@ -0,0 +1,4 @@
+class Foo {
+  static this new() {} // expect error
+  this static new() {} // expect error
+}

test/language/constructor/cannot_be_subscript.wren

@@ -0,0 +1,5 @@
+class Foo {
+  this [value] { // expect error
+    IO.print("ok")
+  }
+}

test/language/constructor/cannot_be_unary.wren

@@ -0,0 +1,5 @@
+class Foo {
+  this ! { // expect error
+    IO.print("ok")
+  }
+}

test/language/constructor/cannot_call_initializer.wren

@@ -0,0 +1,8 @@
+class Foo {
+  this new() {
+    IO.print("ok")
+  }
+}
+
+var foo = Foo.new() // expect: ok
+foo.new() // expect runtime error: Foo does not implement 'new()'.

test/language/constructor/default.wren

@@ -2,7 +2,7 @@ class Foo {
   toString { "Foo" }
 }
 
-// Classes inherit the argument-less "new" one by default.
-var foo = new Foo
+// Classes get an argument-less "new()" by default.
+var foo = Foo.new()
 IO.print(foo is Foo) // expect: true
 IO.print(foo.toString) // expect: Foo

test/language/constructor/default_calls_new.wren

@@ -0,0 +1,9 @@
+class Foo {
+  this new() {
+    IO.print("Foo.new()")
+  }
+}
+
+class Bar is Foo {}
+
+Bar.new() // expect: Foo.new()

test/language/constructor/infix_class_expression.wren

@@ -2,6 +2,8 @@ class Foo {
   +(other) { "Foo " + other }
 }
 
-IO.print(new Foo + "value") // expect: Foo value
+IO.print(Foo.new() + "value") // expect: Foo value
 
 // TODO: Other expressions following a constructor, like new Foo.bar("arg").
+// TODO: Delete this test?
+// TODO: Other constructor tests, like named constructors, etc.

test/language/constructor/named.wren

@@ -0,0 +1,16 @@
+// TODO: Change this.
+
+class Foo {
+  this named() { _field = "named" }
+  this other() { _field = "other" }
+
+  toString { _field }
+}
+
+IO.print(Foo.named()) // expect: named
+IO.print(Foo.other()) // expect: other
+
+// Returns the new instance.
+var foo = Foo.named()
+IO.print(foo is Foo) // expect: true
+IO.print(foo.toString) // expect: named

test/language/constructor/new.wren

@@ -1,19 +0,0 @@
-class Foo {
-  new { IO.print("none") }
-  new() { IO.print("zero") }
-  new(a) { IO.print(a) }
-  new(a, b) { IO.print(a + b) }
-
-  toString { "Foo" }
-}
-
-// Can overload by arity.
-new Foo // expect: none
-new Foo() // expect: zero
-new Foo("one") // expect: one
-new Foo("one", "two") // expect: onetwo
-
-// Returns the new instance.
-var foo = new Foo // expect: none
-IO.print(foo is Foo) // expect: true
-IO.print(foo.toString) // expect: Foo

test/language/constructor/no_default.wren

@@ -0,0 +1,6 @@
+class Foo {
+  this real() {}
+}
+
+// Classes do not get an argument-less "new()" if they define a constructor.
+var foo = Foo.new() // expect runtime error: Foo metaclass does not implement 'new()'.

test/language/constructor/no_parameter_list.wren

@@ -0,0 +1,5 @@
+class Foo {
+  this new { // expect error
+    IO.print("ok")
+  }
+}

test/language/constructor/not_inherited.wren

@@ -0,0 +1,7 @@
+class Foo {
+  this base() {}
+}
+
+class Bar is Foo {}
+
+Bar.base() // expect runtime error: Bar metaclass does not implement 'base()'.

test/language/constructor/object.wren

@@ -0,0 +1,13 @@
+// Tests that Object implements new(). The only way to call that is through a
+// super() call in a subclass, so this does that.
+
+class Foo {
+  this new() {
+    super() // Should not cause a no method error.
+    IO.print("ok")
+  }
+}
+
+Foo.new() // expect: ok
+
+// TODO: Test that can't invoke initializer on existing instance.

test/language/constructor/super_must_have_args.wren

@@ -0,0 +1,7 @@
+class A {}
+
+class B is A {
+  this new() {
+    super // expect error
+  }
+}

test/language/constructor/superclass.wren

@@ -1,5 +1,5 @@
 class A {
-  new(arg) {
+  this new(arg) {
     IO.print("new A ", arg)
     _field = arg
   }
@@ -8,7 +8,7 @@ class A {
 }
 
 class B is A {
-  new(arg1, arg2) {
+  this new(arg1, arg2) {
     super(arg2)
     IO.print("new B ", arg1)
     _field = arg1
@@ -18,7 +18,7 @@ class B is A {
 }
 
 class C is B {
-  new {
+  this new() {
     super("one", "two")
     IO.print("new C")
     _field = "c"
@@ -27,7 +27,7 @@ class C is B {
   cField { _field }
 }
 
-var c = new C
+var c = C.new()
 // expect: new A two
 // expect: new B one
 // expect: new C