Port CFA for expando property access expressions (#4177)

Author: ahejlsberg

internal/checker/checker.go

@@ -11362,18 +11362,21 @@ func (c *Checker) getFlowTypeOfAccessExpression(node *ast.Node, prop *ast.Symbol
 	// and if we are in a constructor of the same class as the property declaration, assume that
 	// the property is uninitialized at the top of the control flow.
 	assumeUninitialized := false
-	initialType := propType
 	if c.strictNullChecks && prop != nil {
-		declaration := prop.ValueDeclaration
-		if declaration != nil && c.strictPropertyInitialization && ast.IsAccessExpression(node) && node.Expression().Kind == ast.KindThisKeyword && c.isPropertyWithoutInitializer(declaration) && !ast.IsStatic(declaration) {
-			flowContainer := c.getControlFlowContainer(node)
-			if ast.IsConstructorDeclaration(flowContainer) && flowContainer.Parent == declaration.Parent && declaration.Flags&ast.NodeFlagsAmbient == 0 {
+		if declaration := prop.ValueDeclaration; declaration != nil {
+			if c.strictPropertyInitialization && ast.IsAccessExpression(node) && node.Expression().Kind == ast.KindThisKeyword &&
+				c.isPropertyWithoutInitializer(declaration) && !ast.IsStatic(declaration) {
+				flowContainer := c.getControlFlowContainer(node)
+				if ast.IsConstructorDeclaration(flowContainer) && flowContainer.Parent == declaration.Parent && declaration.Flags&ast.NodeFlagsAmbient == 0 {
+					assumeUninitialized = true
+				}
+			} else if ast.IsBinaryExpression(declaration) && ast.IsPropertyAccessExpression(declaration.AsBinaryExpression().Left) &&
+				c.getControlFlowContainer(node) == c.getControlFlowContainer(declaration) {
 				assumeUninitialized = true
-				initialType = c.getOptionalType(propType, false /*isProperty*/)
 			}
 		}
 	}
-	flowType := c.getFlowTypeOfReferenceEx(node, propType, initialType, nil, nil)
+	flowType := c.getFlowTypeOfReferenceEx(node, propType, c.addOptionalityEx(propType, false /*isProperty*/, assumeUninitialized), nil, nil)
 	if assumeUninitialized && !c.containsUndefinedType(propType) && c.containsUndefinedType(flowType) {
 		c.error(errorNode, diagnostics.Property_0_is_used_before_being_assigned, c.symbolToString(prop))
 		// Return the declared type to reduce follow-on errors

internal/checker/flow.go

@@ -256,6 +256,13 @@ func (c *Checker) getTypeAtFlowAssignment(f *FlowState, flow *ast.FlowNode) Flow
 		if !c.isReachableFlowNode(flow) {
 			return FlowType{t: c.unreachableNeverType}
 		}
+		// A matching dotted name might also be an expando property on a function *expression*,
+		// in which case we continue control flow analysis back to the function's declaration
+		if ast.IsVariableDeclaration(node) && (ast.IsInJSFile(node) || ast.IsVarConstLike(node)) {
+			if init := node.Initializer(); init != nil && ast.IsFunctionExpressionOrArrowFunction(init) {
+				return c.getTypeAtFlowNode(f, flow.Antecedent)
+			}
+		}
 		return FlowType{t: f.declaredType}
 	}
 	// for (const _ in ref) acts as a nonnull on ref

testdata/baselines/reference/submodule/compiler/classFieldSuperAccessibleJs1.errors.txt

@@ -0,0 +1,18 @@
+index.js(9,23): error TS2565: Property 'blah2' is used before being assigned.
+
+
+==== index.js (1 errors) ====
+    class C {
+      static blah1 = 123;
+    }
+    C.blah2 = 456;
+    
+    class D extends C {
+      static {
+        console.log(super.blah1);
+        console.log(super.blah2);
+                          ~~~~~
+!!! error TS2565: Property 'blah2' is used before being assigned.
+      }
+    }
+    

testdata/baselines/reference/submodule/conformance/jsDeclarationsFunctionsCjs.errors.txt

@@ -1,9 +1,10 @@
 index.js(4,18): error TS2339: Property 'cat' does not exist on type '() => void'.
 index.js(7,18): error TS2339: Property 'Cls' does not exist on type '() => void'.
 index.js(31,18): error TS2339: Property 'self' does not exist on type '<T>(a: T) => T'.
+index.js(57,36): error TS2565: Property 'j' is used before being assigned.
 
 
-==== index.js (3 errors) ====
+==== index.js (4 errors) ====
     module.exports.a = function a() {}
 
     module.exports.b = function b() {}
@@ -67,5 +68,7 @@ index.js(31,18): error TS2339: Property 'self' does not exist on type '<T>(a: T)
 
     // note that this last one doesn't make much sense in cjs, since exports aren't hoisted bindings
     module.exports.jj = module.exports.j;
+                                       ~
+!!! error TS2565: Property 'j' is used before being assigned.
     module.exports.j = function j() {}
 

testdata/baselines/reference/submodule/conformance/jsDeclarationsFunctionsCjs.errors.txt.diff

@@ -1,16 +1,14 @@
 --- old.jsDeclarationsFunctionsCjs.errors.txt
 +++ new.jsDeclarationsFunctionsCjs.errors.txt
 @@= skipped -0, +0 lines =@@
--index.js(57,36): error TS2565: Property 'j' is used before being assigned.
--
--
--==== index.js (1 errors) ====
 +index.js(4,18): error TS2339: Property 'cat' does not exist on type '() => void'.
 +index.js(7,18): error TS2339: Property 'Cls' does not exist on type '() => void'.
 +index.js(31,18): error TS2339: Property 'self' does not exist on type '<T>(a: T) => T'.
-+
-+
-+==== index.js (3 errors) ====
+ index.js(57,36): error TS2565: Property 'j' is used before being assigned.
+
+
+-==== index.js (1 errors) ====
++==== index.js (4 errors) ====
      module.exports.a = function a() {}
 
      module.exports.b = function b() {}
@@ -25,20 +23,12 @@
 
      /**
       * @param {number} a
-@@= skipped -32, +38 lines =@@
+@@= skipped -32, +39 lines =@@
          return a;
      }
      module.exports.f.self = module.exports.f;
 +                     ~~~~
 +!!! error TS2339: Property 'self' does not exist on type '<T>(a: T) => T'.
 
      /**
-      * @param {{x: string}} a
-@@= skipped -26, +28 lines =@@
-     
-     // note that this last one doesn't make much sense in cjs, since exports aren't hoisted bindings
-     module.exports.jj = module.exports.j;
--                                       ~
--!!! error TS2565: Property 'j' is used before being assigned.
-     module.exports.j = function j() {}
-     
+      * @param {{x: string}} a

testdata/baselines/reference/submodule/conformance/typeFromPropertyAssignment36.errors.txt

@@ -0,0 +1,85 @@
+typeFromPropertyAssignment36.ts(11,7): error TS2565: Property 'q' is used before being assigned.
+typeFromPropertyAssignment36.ts(42,3): error TS2565: Property 'q' is used before being assigned.
+typeFromPropertyAssignment36.ts(64,3): error TS2565: Property 'expando' is used before being assigned.
+
+
+==== typeFromPropertyAssignment36.ts (3 errors) ====
+    function f(b: boolean) {
+        function d() {
+        }
+        d.e = 12
+        d.e
+    
+        if (b) {
+            d.q = false
+        }
+        // error d.q might not be assigned
+        d.q
+          ~
+!!! error TS2565: Property 'q' is used before being assigned.
+        if (b) {
+            d.q = false
+        }
+        else {
+            d.q = true
+        }
+        d.q
+        if (b) {
+            d.r = 1
+        }
+        else {
+            d.r = 2
+        }
+        d.r
+        if (b) {
+            d.s = 'hi'
+        }
+        return d
+    }
+    // OK to access possibly-unassigned properties outside the initialising scope
+    var test = f(true).s
+    
+    function d() {
+    }
+    d.e = 12
+    d.e
+    
+    if (!!false) {
+        d.q = false
+    }
+    d.q
+      ~
+!!! error TS2565: Property 'q' is used before being assigned.
+    if (!!false) {
+        d.q = false
+    }
+    else {
+        d.q = true
+    }
+    d.q
+    if (!!false) {
+        d.r = 1
+    }
+    else {
+        d.r = 2
+    }
+    d.r
+    
+    // test function expressions too
+    const g = function() {
+    }
+    if (!!false) {
+        g.expando = 1
+    }
+    g.expando // error
+      ~~~~~~~
+!!! error TS2565: Property 'expando' is used before being assigned.
+    
+    if (!!false) {
+        g.both = 'hi'
+    }
+    else {
+        g.both = 0
+    }
+    g.both
+    

testdata/baselines/reference/submodule/conformance/typeFromPropertyAssignment36.errors.txt.diff

@@ -463,9 +463,6 @@ compiler/invalidUnicodeEscapeSequance2.errors.txt.diff
 compiler/invalidUnicodeEscapeSequance3.errors.txt.diff
 compiler/invalidUnicodeEscapeSequance4.errors.txt.diff
 
-## wrong errors ##
-compiler/classFieldSuperAccessibleJs1.errors.txt.diff
-
 ## deprecated errors ##
 compiler/declarationFileNoCrashOnExtraExportModifier.errors.txt.diff
 compiler/declarationFileNoCrashOnExtraExportModifier.symbols.diff