[bugfix] no-unsafe-any: allow implicitly downcasting any to `unkn…

…own` (palantir#4442)

src/rules/noUnsafeAnyRule.ts

@@ -34,6 +34,7 @@ export class Rule extends Lint.Rules.TypedRule {
         description: Lint.Utils.dedent`
             Warns when using an expression of type 'any' in a dynamic way.
             Uses are only allowed if they would work for \`{} | null | undefined\`.
+            Downcasting to unknown is always safe.
             Type casts and tests are allowed.
             Expressions that work on all values (such as \`"" + x\`) are allowed.`,
         optionsDescription: "Not configurable.",
@@ -153,7 +154,7 @@ class NoUnsafeAnyWalker extends Lint.AbstractWalker<void> {
                     initializer !== undefined &&
                     this.visitNode(
                         initializer,
-                        isPropertyAny(node as ts.PropertyDeclaration, this.checker),
+                        isPropertyAnyOrUnknown(node as ts.PropertyDeclaration, this.checker),
                     )
                 );
             }
@@ -315,7 +316,8 @@ class NoUnsafeAnyWalker extends Lint.AbstractWalker<void> {
 
     private checkContextualType(node: ts.Expression, allowIfNoContextualType?: boolean) {
         const type = this.checker.getContextualType(node);
-        return this.visitNode(node, (type === undefined && allowIfNoContextualType) || isAny(type));
+        const anyOk = (type === undefined && allowIfNoContextualType) || isAny(type, true);
+        return this.visitNode(node, anyOk);
     }
 
     // Allow `const x = foo;` and `const x: any = foo`, but not `const x: Foo = foo;`.
@@ -325,17 +327,15 @@ class NoUnsafeAnyWalker extends Lint.AbstractWalker<void> {
         initializer,
     }: ts.VariableDeclaration | ts.ParameterDeclaration) {
         this.checkBindingName(name);
-        // Always allow the LHS to be `any`. Just don't allow RHS to be `any` when LHS isn't.
-        return (
-            initializer !== undefined &&
-            this.visitNode(
-                initializer,
-                /*anyOk*/
-                (name.kind === ts.SyntaxKind.Identifier &&
-                    (type === undefined || type.kind === ts.SyntaxKind.AnyKeyword)) ||
-                    (type !== undefined && type.kind === ts.SyntaxKind.AnyKeyword),
-            )
-        );
+        // Always allow the LHS to be `any`. Just don't allow RHS to be `any` when LHS isn't `any` or `unknown`.
+        const anyOk =
+            (name.kind === ts.SyntaxKind.Identifier &&
+                (type === undefined ||
+                    type.kind === ts.SyntaxKind.AnyKeyword ||
+                    type.kind === ts.SyntaxKind.UnknownKeyword)) ||
+            (type !== undefined && type.kind === ts.SyntaxKind.AnyKeyword) ||
+            (type !== undefined && type.kind === ts.SyntaxKind.UnknownKeyword);
+        return initializer !== undefined && this.visitNode(initializer, anyOk);
     }
 
     private checkBinaryExpression(node: ts.BinaryExpression, anyOk: boolean | undefined) {
@@ -357,7 +357,7 @@ class NoUnsafeAnyWalker extends Lint.AbstractWalker<void> {
             case ts.SyntaxKind.EqualsToken:
                 // Allow assignment if the lhs is also *any*.
                 allowAnyLeft = true;
-                allowAnyRight = isNodeAny(node.left, this.checker);
+                allowAnyRight = isNodeAny(node.left, this.checker, true);
                 break;
             case ts.SyntaxKind.PlusToken: // Allow implicit stringification
             case ts.SyntaxKind.PlusEqualsToken:
@@ -416,22 +416,28 @@ class NoUnsafeAnyWalker extends Lint.AbstractWalker<void> {
 }
 
 /** Check if property has no type annotation in this class and the base class */
-function isPropertyAny(node: ts.PropertyDeclaration, checker: ts.TypeChecker) {
-    if (!isNodeAny(node.name, checker) || node.name.kind === ts.SyntaxKind.ComputedPropertyName) {
+function isPropertyAnyOrUnknown(node: ts.PropertyDeclaration, checker: ts.TypeChecker) {
+    if (
+        !isNodeAny(node.name, checker, true) ||
+        node.name.kind === ts.SyntaxKind.ComputedPropertyName
+    ) {
         return false;
     }
     for (const base of checker.getBaseTypes(checker.getTypeAtLocation(
         node.parent,
     ) as ts.InterfaceType)) {
         const prop = base.getProperty(node.name.text);
         if (prop !== undefined && prop.declarations !== undefined) {
-            return isAny(checker.getTypeOfSymbolAtLocation(prop, prop.declarations[0]));
+            return isAny(checker.getTypeOfSymbolAtLocation(prop, prop.declarations[0]), true);
         }
     }
     return true;
 }
 
-function isNodeAny(node: ts.Node, checker: ts.TypeChecker): boolean {
+/**
+ * @param orUnknown If true, this function will also return true when the node is unknown.
+ */
+function isNodeAny(node: ts.Node, checker: ts.TypeChecker, orUnknown: boolean = false): boolean {
     let symbol = checker.getSymbolAtLocation(node);
     if (symbol !== undefined && isSymbolFlagSet(symbol, ts.SymbolFlags.Alias)) {
         symbol = checker.getAliasedSymbol(symbol);
@@ -442,7 +448,7 @@ function isNodeAny(node: ts.Node, checker: ts.TypeChecker): boolean {
             return false;
         }
         if (isSymbolFlagSet(symbol, ts.SymbolFlags.Type)) {
-            return isAny(checker.getDeclaredTypeOfSymbol(symbol));
+            return isAny(checker.getDeclaredTypeOfSymbol(symbol), orUnknown);
         }
     }
 
@@ -451,7 +457,7 @@ function isNodeAny(node: ts.Node, checker: ts.TypeChecker): boolean {
         return false;
     }
 
-    return isAny(checker.getTypeAtLocation(node));
+    return isAny(checker.getTypeAtLocation(node), orUnknown);
 }
 
 const jsxElementTypes = new Set<ts.SyntaxKind>([
@@ -477,6 +483,10 @@ function isStringLike(expr: ts.Expression, checker: ts.TypeChecker): boolean {
     return isTypeFlagSet(checker.getTypeAtLocation(expr), ts.TypeFlags.StringLike);
 }
 
-function isAny(type: ts.Type | undefined): boolean {
-    return type !== undefined && isTypeFlagSet(type, ts.TypeFlags.Any);
+function isAny(type: ts.Type | undefined, orUnknown: boolean = false): boolean {
+    return (
+        type !== undefined &&
+        (isTypeFlagSet(type, ts.TypeFlags.Any) ||
+            (orUnknown && isTypeFlagSet(type, ts.TypeFlags.Unknown)))
+    );
 }

test/rules/no-unsafe-any/unknown/test.ts.lint

@@ -0,0 +1,83 @@
+[typescript]: >= 3.0.0
+
+/*
+ * It is not unsafe to pass any where unknown is allowed. This file checks
+ * these uses.
+ */
+
+declare const x: any;
+
+declare function takesUnknown(a: unknown, ...bs: unknown[]): void;
+takesUnknown(x, x);
+
+declare function templateTakesUnknown(arr: TemplateStringsArray, a: unknown, ...bs: unknown[]): any;
+templateTakesUnknown`${x}${x}`;
+
+declare function decoratorTakesUnknown(value: unknown): Function;
+
+class C {
+    @decoratorTakesUnknown(x) f() {}
+}
+
+function f(x: any, retAny: () => any): unknown {
+    const v2: unknown = x;
+    let v5: unknown;
+    v5 = x;
+
+    // Return OK if return type is 'any'
+    return x;
+}
+
+class X {
+    constructor(y: any) {}
+    prop: unknown = x;
+}
+
+takesUnknown(x ? x : x);
+
+function *gen(): IterableIterator<unknown> {
+    yield x;
+}
+
+void x;
+
+{
+    class C {
+        prop: unknown = x;
+    }
+    class D extends C {
+        prop = x;
+    }
+}
+
+function hasThisParameter(this: any) {
+    const u: unknown = this;
+}
+
+(async function(): Promise<unknown> {
+    return x;
+});
+
+const obj = { property: "value" } as any;
+const result: unknown = JSON.parse("{}");
+
+const hasUnknownProp: { prop: unknown, obj: unknown } = { prop: obj, obj };
+hasUnknownProp.prop = obj;
+
+function acceptsUnknown(a: unknown, b: unknown = x) { }
+
+acceptsUnknown(obj);
+
+interface ContainsUnknownProperty {
+    e: unknown;
+}
+
+const p: ContainsUnknownProperty = { e: (123 as any) };
+
+function g() {
+    try {
+
+    } catch (e) {
+        acceptsUnknown(e);
+    }
+}

test/rules/no-unsafe-any/unknown/tsconfig.json

@@ -0,0 +1,7 @@
+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "target": "es6",
+        "experimentalDecorators": true
+    }
+}

test/rules/no-unsafe-any/unknown/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "no-unsafe-any": true
+  }
+}