javascript: new this.constructor() builds the receiver's class at each site

graph/javascript/engine/resolution/value-flow.dl

@@ -370,7 +370,7 @@ installed_function(val, m) :- expr_kind(_, "ASSIGNMENT", _, val), expr_child(_,
 // parser attributes a nested function's body to the nested function, so no
 // filtering by nesting is needed. Plus `@returns {T}`.
 return_value(m, k, i) :- expr_root(_, "RETURN", e), expr_owner(_, m, _, e), !expr_kind(_, "THIS", _, e),
-    !wrapped_result_return(e), expr_value(e, k, i).
+    !wrapped_result_return(e), !returns_own_class_new(m, e), expr_value(e, k, i).
 // A wrapper closure's carrying return keeps every value that does NOT come from the
 // parameter's call: `fn() || fallback`, `override || (cached = make())`, a variable
 // that starts as a default (below). Not an `undefined` placeholder (`let result =
@@ -523,6 +523,26 @@ expr_value(ce, k, i) :- expr_kind(_, "CALL", _, ce), expr_resolves_to_method(ce,
 expr_value(ce, k, i) :- expr_kind(_, "CALL", _, ce), expr_resolves_to_method(ce, m), method_returns_this(m),
     call_site(_, ck, _, _, _, _, ce, _, _), !call_kind_is_member_form(ck),
     this_value(m, k, i).
+// `return new this.constructor(...)` is polymorphic the same way: `clone()` declared on
+// Base and called on a Sub builds a Sub. Read merged, the construction held every
+// instantiated subclass of Base and each call on the clone fanned to all their
+// overrides. So it is not a value of the method either; each site builds an instance of
+// its own receiver's class. (`new this()` in a static is not read this way: the compiler
+// types it as the declaring class, and the oracle would score the receiver's as WRONG.)
+// Returned directly, or through a `const` it initialises (`const c = new
+// this.constructor(); c.x = …; return c`, the everyday clone), which nothing rebinds.
+own_class_new(m, e) :- expr_kind(_, "NEW", _, e), call_site(_, "CONSTRUCTOR_CALL", "constructor", "SYNTACTIC", _, _, e, _, _),
+    expr_child(_, e, "RECEIVER", _, r), expr_kind(_, "THIS", _, r), expr_owner(_, m, _, r).
+returns_own_class_new(m, e) :- expr_root(_, "RETURN", e), expr_owner(_, m, _, e), own_class_new(m, e).
+returns_own_class_new(m, e) :- expr_root(_, "RETURN", e), expr_owner(_, m, _, e), expr_kind(_, "IDENTIFIER", _, e),
+    expr_binding(_, v, e), var_decl(_, _, "CONST_BLOCK_TDZ", _, _, _, v), var_binding_form(_, "IDENTIFIER", v),
+    var_init(_, _, n, v), own_class_new(m, n).
+expr_value(ce, "inst", t) :- expr_kind(_, "CALL", _, ce), expr_resolves_to_method(ce, m), returns_own_class_new(m, _),
+    call_site(_, ck, _, "SYNTACTIC", _, _, ce, _, _), call_kind_is_member_form(ck),
+    expr_child(_, ce, "RECEIVER", _, r), expr_value(r, "inst", t).
+expr_value(ce, "inst", t) :- expr_kind(_, "CALL", _, ce), expr_resolves_to_method(ce, m), returns_own_class_new(m, _),
+    call_site(_, ck, _, _, _, _, ce, _, _), !call_kind_is_member_form(ck),
+    this_value(m, "inst", t).
 
 // ── prop_value(K, I, Name, K2, I2) — reading a property off a value ────────
 // Object literal: `{ a: v }` (key + value children at the same child index),

graph/javascript/souffle/decls_all.dl

@@ -397,6 +397,8 @@
 .decl var_regime_is_block(c0:symbol)
 .decl call_ambient_alternative(c0:symbol)
 .decl method_returns_this(c0:symbol)
+.decl returns_own_class_new(c0:symbol, c1:symbol)
+.decl own_class_new(c0:symbol, c1:symbol)
 .decl module_base_path(c0:symbol, c1:symbol, c2:symbol)
 // ── resolution/arrays.dl: a class extending Map / Set (#619) ──
 .decl coll_ctor(c0:symbol, c1:symbol)

graph/test/javascript/cases/69-this-constructor-per-site/src/main.js

@@ -0,0 +1,43 @@
+'use strict';
+// `new this.constructor()` builds the RECEIVER's class at each site, not every
+// subclass of the class that declares it.
+class Base {
+  clone() { return new this.constructor(); }
+  copy() { return new Base(); }
+  run() { return 'base'; }
+}
+class Sub extends Base { run() { return 'sub'; } }
+class Other extends Base { run() { return 'other'; } }
+
+// The same shape on a constructor function and its prototype.
+function Shape() {}
+Shape.prototype.dup = function () { return new this.constructor(); };
+Shape.prototype.area = function () { return 0; };
+function Circle() { Shape.call(this); }
+Circle.prototype = Object.create(Shape.prototype);
+Circle.prototype.constructor = Circle;
+Circle.prototype.area = function () { return 3; };
+
+// The everyday clone: built into a `const`, filled in, returned.
+class Query {
+  clone() { const q = new this.constructor(); q.opts = this.opts; return q; }
+  // Control: a `let` may be rebound before the return, so it keeps its merged value.
+  fork() { let q = new this.constructor(); return q; }
+  exec() { return 'query'; }
+}
+class Select extends Query { exec() { return 'select'; } }
+
+function main() {
+  new Select().clone().exec();
+  new Query().clone().exec();
+  new Select().fork().exec();
+  new Sub().clone().run();
+  new Other().clone().run();
+  new Sub().clone().clone().run();
+  new Base().clone().run();
+  // Control: a fixed `new Base()` stays Base whatever the receiver.
+  new Sub().copy().run();
+  new Circle().dup().area();
+  new Shape().dup().area();
+}
+main();

graph/test/javascript/cases/69-this-constructor-per-site/src/package.json

@@ -0,0 +1 @@
+{ "name": "this-constructor-per-site" }

graph/test/javascript/expected/07-esm-class-hierarchy.edges

@@ -10,8 +10,7 @@ Component.js:7:15 CONSTRUCTOR_CALL AbstractBlock  ->  known_edge  AbstractBlock.
 Component.js:7:5 METHOD_CALL block.add  ->  known_edge  Node.js:8:3 add
 Component.js:7:5 METHOD_CALL block.add(new AbstractBlock(this)).walk  ->  known_edge  AbstractBlock.js:4:3 walk
 Component.js:8:18 METHOD_CALL block.clone  ->  known_edge  Node.js:9:3 clone
-Component.js:9:5 METHOD_CALL copy.walk  ->  multi_inferred  AbstractBlock.js:4:3 walk
-Component.js:9:5 METHOD_CALL copy.walk  ->  multi_inferred  Node.js:7:3 walk
+Component.js:9:5 METHOD_CALL copy.walk  ->  known_edge  AbstractBlock.js:4:3 walk
 Node.js:7:12 METHOD_CALL this.component.warn  ->  known_edge  Component.js:3:3 warn
 Node.js:7:39 METHOD_CALL this.children.forEach  ->  ambient_terminal  -
 Node.js:7:39 METHOD_CALL this.children.forEach  ->  callback_registered  Node.js:7:61 <arrow>

graph/test/javascript/expected/37-this-constructor.edges

@@ -1,14 +1,12 @@
 main.js:11:13 CONSTRUCTOR_CALL Sub  ->  implicit_constructor  -
 main.js:12:3 METHOD_CALL s.clone  ->  known_edge  main.js:3:3 clone
-main.js:12:3 METHOD_CALL s.clone().run  ->  multi_inferred  main.js:5:3 run
-main.js:12:3 METHOD_CALL s.clone().run  ->  multi_inferred  main.js:8:26 run
+main.js:12:3 METHOD_CALL s.clone().run  ->  known_edge  main.js:8:26 run
 main.js:13:3 METHOD_CALL Sub.build  ->  known_edge  main.js:6:3 build
 main.js:13:3 METHOD_CALL Sub.build().run  ->  multi_inferred  main.js:5:3 run
 main.js:13:3 METHOD_CALL Sub.build().run  ->  multi_inferred  main.js:8:26 run
 main.js:14:3 CONSTRUCTOR_CALL Base  ->  implicit_constructor  -
 main.js:14:3 METHOD_CALL new Base().make  ->  known_edge  main.js:4:3 make
-main.js:14:3 METHOD_CALL new Base().make().run  ->  multi_inferred  main.js:5:3 run
-main.js:14:3 METHOD_CALL new Base().make().run  ->  multi_inferred  main.js:8:26 run
+main.js:14:3 METHOD_CALL new Base().make().run  ->  known_edge  main.js:5:3 run
 main.js:16:1 FUNCTION_CALL main  ->  known_edge  main.js:10:1 main
 main.js:3:20 CONSTRUCTOR_CALL this.constructor  ->  implicit_constructor  -
 main.js:4:19 CONSTRUCTOR_CALL this.constructor  ->  implicit_constructor  -

graph/test/javascript/expected/69-this-constructor-per-site.diag

@@ -0,0 +1,2 @@
+package_entry    this-constructor-per-site  .  []  DEFAULT_INDEX  index.js  MISSING_FILE  -> -
+unresolved       main.js:17:20  METHOD_CALL create  no_target

graph/test/javascript/expected/69-this-constructor-per-site.edges

@@ -0,0 +1,41 @@
+main.js:14:44 CONSTRUCTOR_CALL this.constructor  ->  multi_inferred  main.js:13:1 Shape
+main.js:14:44 CONSTRUCTOR_CALL this.constructor  ->  multi_inferred  main.js:16:1 Circle
+main.js:16:21 FUNCTION_CALL_CALL Shape.call  ->  known_edge  main.js:13:1 Shape
+main.js:17:20 METHOD_CALL Object.create  ->  ambient_terminal  -
+main.js:23:23 CONSTRUCTOR_CALL this.constructor  ->  implicit_constructor  -
+main.js:25:20 CONSTRUCTOR_CALL this.constructor  ->  implicit_constructor  -
+main.js:31:3 CONSTRUCTOR_CALL Select  ->  implicit_constructor  -
+main.js:31:3 METHOD_CALL new Select().clone  ->  known_edge  main.js:23:3 clone
+main.js:31:3 METHOD_CALL new Select().clone().exec  ->  known_edge  main.js:28:30 exec
+main.js:32:3 CONSTRUCTOR_CALL Query  ->  implicit_constructor  -
+main.js:32:3 METHOD_CALL new Query().clone  ->  known_edge  main.js:23:3 clone
+main.js:32:3 METHOD_CALL new Query().clone().exec  ->  known_edge  main.js:26:3 exec
+main.js:33:3 CONSTRUCTOR_CALL Select  ->  implicit_constructor  -
+main.js:33:3 METHOD_CALL new Select().fork  ->  known_edge  main.js:25:3 fork
+main.js:33:3 METHOD_CALL new Select().fork().exec  ->  multi_inferred  main.js:26:3 exec
+main.js:33:3 METHOD_CALL new Select().fork().exec  ->  multi_inferred  main.js:28:30 exec
+main.js:34:3 CONSTRUCTOR_CALL Sub  ->  implicit_constructor  -
+main.js:34:3 METHOD_CALL new Sub().clone  ->  known_edge  main.js:5:3 clone
+main.js:34:3 METHOD_CALL new Sub().clone().run  ->  known_edge  main.js:9:26 run
+main.js:35:3 CONSTRUCTOR_CALL Other  ->  implicit_constructor  -
+main.js:35:3 METHOD_CALL new Other().clone  ->  known_edge  main.js:5:3 clone
+main.js:35:3 METHOD_CALL new Other().clone().run  ->  known_edge  main.js:10:28 run
+main.js:36:3 CONSTRUCTOR_CALL Sub  ->  implicit_constructor  -
+main.js:36:3 METHOD_CALL new Sub().clone  ->  known_edge  main.js:5:3 clone
+main.js:36:3 METHOD_CALL new Sub().clone().clone  ->  known_edge  main.js:5:3 clone
+main.js:36:3 METHOD_CALL new Sub().clone().clone().run  ->  known_edge  main.js:9:26 run
+main.js:37:3 CONSTRUCTOR_CALL Base  ->  implicit_constructor  -
+main.js:37:3 METHOD_CALL new Base().clone  ->  known_edge  main.js:5:3 clone
+main.js:37:3 METHOD_CALL new Base().clone().run  ->  known_edge  main.js:7:3 run
+main.js:39:3 CONSTRUCTOR_CALL Sub  ->  implicit_constructor  -
+main.js:39:3 METHOD_CALL new Sub().copy  ->  known_edge  main.js:6:3 copy
+main.js:39:3 METHOD_CALL new Sub().copy().run  ->  known_edge  main.js:7:3 run
+main.js:40:3 CONSTRUCTOR_CALL Circle  ->  known_edge  main.js:16:1 Circle
+main.js:40:3 METHOD_CALL new Circle().dup  ->  known_edge  main.js:14:23 dup
+main.js:40:3 METHOD_CALL new Circle().dup().area  ->  known_edge  main.js:19:25 area
+main.js:41:3 CONSTRUCTOR_CALL Shape  ->  known_edge  main.js:13:1 Shape
+main.js:41:3 METHOD_CALL new Shape().dup  ->  known_edge  main.js:14:23 dup
+main.js:41:3 METHOD_CALL new Shape().dup().area  ->  known_edge  main.js:15:24 area
+main.js:43:1 FUNCTION_CALL main  ->  known_edge  main.js:30:1 main
+main.js:5:20 CONSTRUCTOR_CALL this.constructor  ->  implicit_constructor  -
+main.js:6:19 CONSTRUCTOR_CALL Base  ->  implicit_constructor  -

graph/test/javascript/expected/69-this-constructor-per-site.oracle

@@ -0,0 +1,29 @@
+main.js:14:44 CONSTRUCTOR_CALL constructor  SYNTHESIZED_OVER  main.js:13:1;main.js:16:1
+main.js:16:21 FUNCTION_CALL_CALL call  EXACT  main.js:13:1
+main.js:17:20 METHOD_CALL create  LIB_AMBIENT_OK  
+main.js:23:23 CONSTRUCTOR_CALL constructor  SYNTHESIZED_OK  
+main.js:25:20 CONSTRUCTOR_CALL constructor  SYNTHESIZED_OK  
+main.js:31:3 CONSTRUCTOR_CALL Select  SYNTHESIZED_OK  
+main.js:31:3 METHOD_CALL clone  EXACT  main.js:23:3
+main.js:32:3 CONSTRUCTOR_CALL Query  SYNTHESIZED_OK  
+main.js:32:3 METHOD_CALL clone  EXACT  main.js:23:3
+main.js:33:3 CONSTRUCTOR_CALL Select  SYNTHESIZED_OK  
+main.js:33:3 METHOD_CALL fork  EXACT  main.js:25:3
+main.js:34:3 CONSTRUCTOR_CALL Sub  SYNTHESIZED_OK  
+main.js:34:3 METHOD_CALL clone  EXACT  main.js:5:3
+main.js:35:3 CONSTRUCTOR_CALL Other  SYNTHESIZED_OK  
+main.js:35:3 METHOD_CALL clone  EXACT  main.js:5:3
+main.js:36:3 CONSTRUCTOR_CALL Sub  SYNTHESIZED_OK  
+main.js:36:3 METHOD_CALL clone  EXACT  main.js:5:3
+main.js:37:3 CONSTRUCTOR_CALL Base  SYNTHESIZED_OK  
+main.js:37:3 METHOD_CALL clone  EXACT  main.js:5:3
+main.js:39:3 CONSTRUCTOR_CALL Sub  SYNTHESIZED_OK  
+main.js:39:3 METHOD_CALL copy  EXACT  main.js:6:3
+main.js:39:3 METHOD_CALL run  EXACT  main.js:7:3
+main.js:40:3 CONSTRUCTOR_CALL Circle  EXACT  main.js:16:1
+main.js:41:3 CONSTRUCTOR_CALL Shape  EXACT  main.js:13:1
+main.js:41:3 METHOD_CALL dup  EXACT  main.js:14:23
+main.js:43:1 FUNCTION_CALL main  EXACT  main.js:30:1
+main.js:5:20 CONSTRUCTOR_CALL constructor  SYNTHESIZED_OK  
+main.js:6:19 CONSTRUCTOR_CALL Base  SYNTHESIZED_OK  
+# defects: 0