Definite assignment checking for expando properties (#27128)

src/compiler/checker.ts

@@ -14734,6 +14734,14 @@ namespace ts {
                 // reference 'x.y.z', we may be at an assignment to 'x.y' or 'x'. In that case,
                 // return the declared type.
                 if (containsMatchingReference(reference, node)) {
+                    // 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 (isVariableDeclaration(node) && (isInJSFile(node) || isVarConst(node))) {
+                        const init = getDeclaredExpandoInitializer(node);
+                        if (init && (init.kind === SyntaxKind.FunctionExpression || init.kind === SyntaxKind.ArrowFunction)) {
+                            return getTypeAtFlowNode(flow.antecedent);
+                        }
+                    }
                     return declaredType;
                 }
                 // Assignment doesn't affect reference
@@ -18395,6 +18403,9 @@ namespace ts {
                     }
                 }
             }
+            else if (strictNullChecks && prop && prop.valueDeclaration && isPropertyAccessExpression(prop.valueDeclaration) && getAssignmentDeclarationPropertyAccessKind(prop.valueDeclaration)) {
+                assumeUninitialized = true;
+            }
             const flowType = getFlowTypeOfReference(node, propType, assumeUninitialized ? getOptionalType(propType) : propType);
             if (assumeUninitialized && !(getFalsyFlags(propType) & TypeFlags.Undefined) && getFalsyFlags(flowType) & TypeFlags.Undefined) {
                 error(right, Diagnostics.Property_0_is_used_before_being_assigned, symbolToString(prop!)); // TODO: GH#18217

tests/baselines/reference/typeFromPropertyAssignment36.errors.txt

@@ -0,0 +1,85 @@
+tests/cases/conformance/salsa/typeFromPropertyAssignment36.ts(11,7): error TS2565: Property 'q' is used before being assigned.
+tests/cases/conformance/salsa/typeFromPropertyAssignment36.ts(42,3): error TS2565: Property 'q' is used before being assigned.
+tests/cases/conformance/salsa/typeFromPropertyAssignment36.ts(64,3): error TS2565: Property 'expando' is used before being assigned.
+
+
+==== tests/cases/conformance/salsa/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
+    

tests/baselines/reference/typeFromPropertyAssignment36.js

@@ -0,0 +1,144 @@
+//// [typeFromPropertyAssignment36.ts]
+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
+    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
+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
+
+if (!!false) {
+    g.both = 'hi'
+}
+else {
+    g.both = 0
+}
+g.both
+
+
+//// [typeFromPropertyAssignment36.js]
+"use strict";
+function f(b) {
+    function d() {
+    }
+    d.e = 12;
+    d.e;
+    if (b) {
+        d.q = false;
+    }
+    // error d.q might not be assigned
+    d.q;
+    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;
+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
+var g = function () {
+};
+if (!!false) {
+    g.expando = 1;
+}
+g.expando; // error
+if (!!false) {
+    g.both = 'hi';
+}
+else {
+    g.both = 0;
+}
+g.both;

tests/baselines/reference/typeFromPropertyAssignment36.symbols

@@ -0,0 +1,178 @@
+=== tests/cases/conformance/salsa/typeFromPropertyAssignment36.ts ===
+function f(b: boolean) {
+>f : Symbol(f, Decl(typeFromPropertyAssignment36.ts, 0, 0))
+>b : Symbol(b, Decl(typeFromPropertyAssignment36.ts, 0, 11))
+
+    function d() {
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+    }
+    d.e = 12
+>d.e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 2, 5))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 2, 5))
+
+    d.e
+>d.e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 2, 5))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 2, 5))
+
+    if (b) {
+>b : Symbol(b, Decl(typeFromPropertyAssignment36.ts, 0, 11))
+
+        d.q = false
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+    }
+    // error d.q might not be assigned
+    d.q
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+
+    if (b) {
+>b : Symbol(b, Decl(typeFromPropertyAssignment36.ts, 0, 11))
+
+        d.q = false
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+    }
+    else {
+        d.q = true
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+    }
+    d.q
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 6, 12), Decl(typeFromPropertyAssignment36.ts, 11, 12), Decl(typeFromPropertyAssignment36.ts, 14, 10))
+
+    if (b) {
+>b : Symbol(b, Decl(typeFromPropertyAssignment36.ts, 0, 11))
+
+        d.r = 1
+>d.r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 18, 12), Decl(typeFromPropertyAssignment36.ts, 21, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 18, 12), Decl(typeFromPropertyAssignment36.ts, 21, 10))
+    }
+    else {
+        d.r = 2
+>d.r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 18, 12), Decl(typeFromPropertyAssignment36.ts, 21, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 18, 12), Decl(typeFromPropertyAssignment36.ts, 21, 10))
+    }
+    d.r
+>d.r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 18, 12), Decl(typeFromPropertyAssignment36.ts, 21, 10))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 18, 12), Decl(typeFromPropertyAssignment36.ts, 21, 10))
+
+    if (b) {
+>b : Symbol(b, Decl(typeFromPropertyAssignment36.ts, 0, 11))
+
+        d.s = 'hi'
+>d.s : Symbol(d.s, Decl(typeFromPropertyAssignment36.ts, 25, 12))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+>s : Symbol(d.s, Decl(typeFromPropertyAssignment36.ts, 25, 12))
+    }
+    return d
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 0, 24))
+}
+// OK to access possibly-unassigned properties outside the initialising scope
+var test = f(true).s
+>test : Symbol(test, Decl(typeFromPropertyAssignment36.ts, 31, 3))
+>f(true).s : Symbol(d.s, Decl(typeFromPropertyAssignment36.ts, 25, 12))
+>f : Symbol(f, Decl(typeFromPropertyAssignment36.ts, 0, 0))
+>s : Symbol(d.s, Decl(typeFromPropertyAssignment36.ts, 25, 12))
+
+function d() {
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+}
+d.e = 12
+>d.e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 34, 1))
+
+d.e
+>d.e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>e : Symbol(d.e, Decl(typeFromPropertyAssignment36.ts, 34, 1))
+
+if (!!false) {
+    d.q = false
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+}
+d.q
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+
+if (!!false) {
+    d.q = false
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+}
+else {
+    d.q = true
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+}
+d.q
+>d.q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>q : Symbol(d.q, Decl(typeFromPropertyAssignment36.ts, 38, 14), Decl(typeFromPropertyAssignment36.ts, 42, 14), Decl(typeFromPropertyAssignment36.ts, 45, 6))
+
+if (!!false) {
+    d.r = 1
+>d.r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 49, 14), Decl(typeFromPropertyAssignment36.ts, 52, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 49, 14), Decl(typeFromPropertyAssignment36.ts, 52, 6))
+}
+else {
+    d.r = 2
+>d.r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 49, 14), Decl(typeFromPropertyAssignment36.ts, 52, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 49, 14), Decl(typeFromPropertyAssignment36.ts, 52, 6))
+}
+d.r
+>d.r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 49, 14), Decl(typeFromPropertyAssignment36.ts, 52, 6))
+>d : Symbol(d, Decl(typeFromPropertyAssignment36.ts, 31, 20), Decl(typeFromPropertyAssignment36.ts, 34, 1))
+>r : Symbol(d.r, Decl(typeFromPropertyAssignment36.ts, 49, 14), Decl(typeFromPropertyAssignment36.ts, 52, 6))
+
+// test function expressions too
+const g = function() {
+>g : Symbol(g, Decl(typeFromPropertyAssignment36.ts, 58, 5))
+}
+if (!!false) {
+    g.expando = 1
+>g.expando : Symbol(g.expando, Decl(typeFromPropertyAssignment36.ts, 60, 14))
+>g : Symbol(g, Decl(typeFromPropertyAssignment36.ts, 58, 5))
+>expando : Symbol(g.expando, Decl(typeFromPropertyAssignment36.ts, 60, 14))
+}
+g.expando // error
+>g.expando : Symbol(g.expando, Decl(typeFromPropertyAssignment36.ts, 60, 14))
+>g : Symbol(g, Decl(typeFromPropertyAssignment36.ts, 58, 5))
+>expando : Symbol(g.expando, Decl(typeFromPropertyAssignment36.ts, 60, 14))
+
+if (!!false) {
+    g.both = 'hi'
+>g.both : Symbol(g.both, Decl(typeFromPropertyAssignment36.ts, 65, 14), Decl(typeFromPropertyAssignment36.ts, 68, 6))
+>g : Symbol(g, Decl(typeFromPropertyAssignment36.ts, 58, 5))
+>both : Symbol(g.both, Decl(typeFromPropertyAssignment36.ts, 65, 14), Decl(typeFromPropertyAssignment36.ts, 68, 6))
+}
+else {
+    g.both = 0
+>g.both : Symbol(g.both, Decl(typeFromPropertyAssignment36.ts, 65, 14), Decl(typeFromPropertyAssignment36.ts, 68, 6))
+>g : Symbol(g, Decl(typeFromPropertyAssignment36.ts, 58, 5))
+>both : Symbol(g.both, Decl(typeFromPropertyAssignment36.ts, 65, 14), Decl(typeFromPropertyAssignment36.ts, 68, 6))
+}
+g.both
+>g.both : Symbol(g.both, Decl(typeFromPropertyAssignment36.ts, 65, 14), Decl(typeFromPropertyAssignment36.ts, 68, 6))
+>g : Symbol(g, Decl(typeFromPropertyAssignment36.ts, 58, 5))
+>both : Symbol(g.both, Decl(typeFromPropertyAssignment36.ts, 65, 14), Decl(typeFromPropertyAssignment36.ts, 68, 6))
+

tests/baselines/reference/typeFromPropertyAssignment36.types

@@ -0,0 +1,233 @@
+=== tests/cases/conformance/salsa/typeFromPropertyAssignment36.ts ===
+function f(b: boolean) {
+>f : (b: boolean) => { (): void; e: number; q: boolean; r: number; s: string; }
+>b : boolean
+
+    function d() {
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+    }
+    d.e = 12
+>d.e = 12 : 12
+>d.e : number
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>e : number
+>12 : 12
+
+    d.e
+>d.e : number
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>e : number
+
+    if (b) {
+>b : boolean
+
+        d.q = false
+>d.q = false : false
+>d.q : boolean
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>q : boolean
+>false : false
+    }
+    // error d.q might not be assigned
+    d.q
+>d.q : boolean
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>q : boolean
+
+    if (b) {
+>b : boolean
+
+        d.q = false
+>d.q = false : false
+>d.q : boolean
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>q : boolean
+>false : false
+    }
+    else {
+        d.q = true
+>d.q = true : true
+>d.q : boolean
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>q : boolean
+>true : true
+    }
+    d.q
+>d.q : boolean
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>q : boolean
+
+    if (b) {
+>b : boolean
+
+        d.r = 1
+>d.r = 1 : 1
+>d.r : number
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>r : number
+>1 : 1
+    }
+    else {
+        d.r = 2
+>d.r = 2 : 2
+>d.r : number
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>r : number
+>2 : 2
+    }
+    d.r
+>d.r : number
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>r : number
+
+    if (b) {
+>b : boolean
+
+        d.s = 'hi'
+>d.s = 'hi' : "hi"
+>d.s : string
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+>s : string
+>'hi' : "hi"
+    }
+    return d
+>d : { (): void; e: number; q: boolean; r: number; s: string; }
+}
+// OK to access possibly-unassigned properties outside the initialising scope
+var test = f(true).s
+>test : string
+>f(true).s : string
+>f(true) : { (): void; e: number; q: boolean; r: number; s: string; }
+>f : (b: boolean) => { (): void; e: number; q: boolean; r: number; s: string; }
+>true : true
+>s : string
+
+function d() {
+>d : typeof d
+}
+d.e = 12
+>d.e = 12 : 12
+>d.e : number
+>d : typeof d
+>e : number
+>12 : 12
+
+d.e
+>d.e : number
+>d : typeof d
+>e : number
+
+if (!!false) {
+>!!false : false
+>!false : true
+>false : false
+
+    d.q = false
+>d.q = false : false
+>d.q : boolean
+>d : typeof d
+>q : boolean
+>false : false
+}
+d.q
+>d.q : boolean
+>d : typeof d
+>q : boolean
+
+if (!!false) {
+>!!false : false
+>!false : true
+>false : false
+
+    d.q = false
+>d.q = false : false
+>d.q : boolean
+>d : typeof d
+>q : boolean
+>false : false
+}
+else {
+    d.q = true
+>d.q = true : true
+>d.q : boolean
+>d : typeof d
+>q : boolean
+>true : true
+}
+d.q
+>d.q : boolean
+>d : typeof d
+>q : boolean
+
+if (!!false) {
+>!!false : false
+>!false : true
+>false : false
+
+    d.r = 1
+>d.r = 1 : 1
+>d.r : number
+>d : typeof d
+>r : number
+>1 : 1
+}
+else {
+    d.r = 2
+>d.r = 2 : 2
+>d.r : number
+>d : typeof d
+>r : number
+>2 : 2
+}
+d.r
+>d.r : number
+>d : typeof d
+>r : number
+
+// test function expressions too
+const g = function() {
+>g : { (): void; expando: number; both: string | number; }
+>function() {} : { (): void; expando: number; both: string | number; }
+}
+if (!!false) {
+>!!false : false
+>!false : true
+>false : false
+
+    g.expando = 1
+>g.expando = 1 : 1
+>g.expando : number
+>g : { (): void; expando: number; both: string | number; }
+>expando : number
+>1 : 1
+}
+g.expando // error
+>g.expando : number
+>g : { (): void; expando: number; both: string | number; }
+>expando : number
+
+if (!!false) {
+>!!false : false
+>!false : true
+>false : false
+
+    g.both = 'hi'
+>g.both = 'hi' : "hi"
+>g.both : string | number
+>g : { (): void; expando: number; both: string | number; }
+>both : string | number
+>'hi' : "hi"
+}
+else {
+    g.both = 0
+>g.both = 0 : 0
+>g.both : string | number
+>g : { (): void; expando: number; both: string | number; }
+>both : string | number
+>0 : 0
+}
+g.both
+>g.both : string | number
+>g : { (): void; expando: number; both: string | number; }
+>both : string | number
+

tests/cases/conformance/salsa/typeFromPropertyAssignment36.ts

@@ -0,0 +1,73 @@
+// @strict: true
+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
+    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
+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
+
+if (!!false) {
+    g.both = 'hi'
+}
+else {
+    g.both = 0
+}
+g.both