Support prototype assignment with a function declaration (#25300)

Previously variable declaration+function expression worked.
Note that class expression/class declaration do not work, due to the way
they are specified. I added a test for future reference.

src/compiler/checker.ts

@@ -19458,7 +19458,8 @@ namespace ts {
         function getAssignedClassType(symbol: Symbol) {
             const decl = symbol.valueDeclaration;
             const assignmentSymbol = decl && decl.parent &&
-                (isBinaryExpression(decl.parent) && getSymbolOfNode(decl.parent.left) ||
+                (isFunctionDeclaration(decl) && getSymbolOfNode(decl) ||
+                 isBinaryExpression(decl.parent) && getSymbolOfNode(decl.parent.left) ||
                  isVariableDeclaration(decl.parent) && getSymbolOfNode(decl.parent));
             if (assignmentSymbol) {
                 const prototype = forEach(assignmentSymbol.declarations, getAssignedJavascriptPrototype);

tests/baselines/reference/typeFromPropertyAssignment27.symbols

@@ -0,0 +1,26 @@
+=== tests/cases/conformance/salsa/a.js ===
+// mixed prototype-assignment+function declaration
+function C() { this.p = 1; }
+>C : Symbol(C, Decl(a.js, 0, 0), Decl(a.js, 1, 28))
+>p : Symbol(C.p, Decl(a.js, 1, 14))
+
+C.prototype = { q: 2 };
+>C.prototype : Symbol(C.prototype, Decl(a.js, 1, 28))
+>C : Symbol(C, Decl(a.js, 0, 0), Decl(a.js, 1, 28))
+>prototype : Symbol(C.prototype, Decl(a.js, 1, 28))
+>q : Symbol(q, Decl(a.js, 2, 15))
+
+const c = new C()
+>c : Symbol(c, Decl(a.js, 4, 5))
+>C : Symbol(C, Decl(a.js, 0, 0), Decl(a.js, 1, 28))
+
+c.p
+>c.p : Symbol(C.p, Decl(a.js, 1, 14))
+>c : Symbol(c, Decl(a.js, 4, 5))
+>p : Symbol(C.p, Decl(a.js, 1, 14))
+
+c.q
+>c.q : Symbol(q, Decl(a.js, 2, 15))
+>c : Symbol(c, Decl(a.js, 4, 5))
+>q : Symbol(q, Decl(a.js, 2, 15))
+

tests/baselines/reference/typeFromPropertyAssignment27.types

@@ -0,0 +1,34 @@
+=== tests/cases/conformance/salsa/a.js ===
+// mixed prototype-assignment+function declaration
+function C() { this.p = 1; }
+>C : typeof C
+>this.p = 1 : 1
+>this.p : any
+>this : any
+>p : any
+>1 : 1
+
+C.prototype = { q: 2 };
+>C.prototype = { q: 2 } : { [x: string]: any; q: number; }
+>C.prototype : { [x: string]: any; }
+>C : typeof C
+>prototype : { [x: string]: any; }
+>{ q: 2 } : { [x: string]: any; q: number; }
+>q : number
+>2 : 2
+
+const c = new C()
+>c : C & { [x: string]: any; q: number; }
+>new C() : C & { [x: string]: any; q: number; }
+>C : typeof C
+
+c.p
+>c.p : number
+>c : C & { [x: string]: any; q: number; }
+>p : number
+
+c.q
+>c.q : number
+>c : C & { [x: string]: any; q: number; }
+>q : number
+

tests/baselines/reference/typeFromPropertyAssignment28.errors.txt

@@ -0,0 +1,23 @@
+tests/cases/conformance/salsa/a.js(7,17): error TS2322: Type '{ [x: string]: any; q: number; }' is not assignable to type 'C'.
+  Object literal may only specify known properties, and 'q' does not exist in type 'C'.
+tests/cases/conformance/salsa/a.js(11,3): error TS2339: Property 'q' does not exist on type 'C'.
+
+
+==== tests/cases/conformance/salsa/a.js (2 errors) ====
+    // mixed prototype-assignment+class declaration
+    class C { constructor() { this.p = 1; } }
+    // Property assignment does nothing.
+    // You have to use Object.defineProperty(C, "prototype", { q: 2 })
+    // and that only works on classes with no superclass.
+    // (Object.defineProperty isn't recognised as a JS special assignment right now.)
+    C.prototype = { q: 2 };
+                    ~~~~
+!!! error TS2322: Type '{ [x: string]: any; q: number; }' is not assignable to type 'C'.
+!!! error TS2322:   Object literal may only specify known properties, and 'q' does not exist in type 'C'.
+    
+    const c = new C()
+    c.p
+    c.q
+      ~
+!!! error TS2339: Property 'q' does not exist on type 'C'.
+    

tests/baselines/reference/typeFromPropertyAssignment28.symbols

@@ -0,0 +1,30 @@
+=== tests/cases/conformance/salsa/a.js ===
+// mixed prototype-assignment+class declaration
+class C { constructor() { this.p = 1; } }
+>C : Symbol(C, Decl(a.js, 0, 0), Decl(a.js, 1, 41))
+>this.p : Symbol(C.p, Decl(a.js, 1, 25))
+>this : Symbol(C, Decl(a.js, 0, 0), Decl(a.js, 1, 41))
+>p : Symbol(C.p, Decl(a.js, 1, 25))
+
+// Property assignment does nothing.
+// You have to use Object.defineProperty(C, "prototype", { q: 2 })
+// and that only works on classes with no superclass.
+// (Object.defineProperty isn't recognised as a JS special assignment right now.)
+C.prototype = { q: 2 };
+>C.prototype : Symbol(C.prototype, Decl(a.js, 1, 41))
+>C : Symbol(C, Decl(a.js, 0, 0), Decl(a.js, 1, 41))
+>prototype : Symbol(C.prototype, Decl(a.js, 1, 41))
+>q : Symbol(q, Decl(a.js, 6, 15))
+
+const c = new C()
+>c : Symbol(c, Decl(a.js, 8, 5))
+>C : Symbol(C, Decl(a.js, 0, 0), Decl(a.js, 1, 41))
+
+c.p
+>c.p : Symbol(C.p, Decl(a.js, 1, 25))
+>c : Symbol(c, Decl(a.js, 8, 5))
+>p : Symbol(C.p, Decl(a.js, 1, 25))
+
+c.q
+>c : Symbol(c, Decl(a.js, 8, 5))
+

tests/baselines/reference/typeFromPropertyAssignment28.types

@@ -0,0 +1,38 @@
+=== tests/cases/conformance/salsa/a.js ===
+// mixed prototype-assignment+class declaration
+class C { constructor() { this.p = 1; } }
+>C : C
+>this.p = 1 : 1
+>this.p : number
+>this : this
+>p : number
+>1 : 1
+
+// Property assignment does nothing.
+// You have to use Object.defineProperty(C, "prototype", { q: 2 })
+// and that only works on classes with no superclass.
+// (Object.defineProperty isn't recognised as a JS special assignment right now.)
+C.prototype = { q: 2 };
+>C.prototype = { q: 2 } : { [x: string]: any; q: number; }
+>C.prototype : C
+>C : typeof C
+>prototype : C
+>{ q: 2 } : { [x: string]: any; q: number; }
+>q : number
+>2 : 2
+
+const c = new C()
+>c : C
+>new C() : C
+>C : typeof C
+
+c.p
+>c.p : number
+>c : C
+>p : number
+
+c.q
+>c.q : any
+>c : C
+>q : any
+

tests/cases/conformance/salsa/typeFromPropertyAssignment27.ts

@@ -0,0 +1,11 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @Filename: a.js
+// mixed prototype-assignment+function declaration
+function C() { this.p = 1; }
+C.prototype = { q: 2 };
+
+const c = new C()
+c.p
+c.q

tests/cases/conformance/salsa/typeFromPropertyAssignment28.ts

@@ -0,0 +1,15 @@
+// @noEmit: true
+// @allowJs: true
+// @checkJs: true
+// @Filename: a.js
+// mixed prototype-assignment+class declaration
+class C { constructor() { this.p = 1; } }
+// Property assignment does nothing.
+// You have to use Object.defineProperty(C, "prototype", { q: 2 })
+// and that only works on classes with no superclass.
+// (Object.defineProperty isn't recognised as a JS special assignment right now.)
+C.prototype = { q: 2 };
+
+const c = new C()
+c.p
+c.q