Merge pull request #20375 from asgerf/js/promise-try

JS: Support Promise.try and Array.prototype.with

Author: asgerf

javascript/ql/lib/semmle/javascript/internal/flow_summaries/Arrays.qll

@@ -544,6 +544,25 @@ class ToSpliced extends SummarizedCallable {
   }
 }
 
+class With extends SummarizedCallable {
+  With() { this = "Array#with" }
+
+  override InstanceCall getACallSimple() { result.getMethodName() = "with" }
+
+  override predicate propagatesFlow(string input, string output, boolean preservesValue) {
+    preservesValue = true and
+    (
+      // Copy all elements from the original array to the new array
+      input = "Argument[this].WithArrayElement" and
+      output = "ReturnValue"
+      or
+      // Replace the value at the specified index
+      input = "Argument[1]" and
+      output = "ReturnValue.ArrayElement"
+    )
+  }
+}
+
 class ArrayCoercionPackage extends FunctionalPackageSummary {
   ArrayCoercionPackage() { this = "ArrayCoercionPackage" }
 

javascript/ql/lib/semmle/javascript/internal/flow_summaries/FlowSummaryUtil.qll

@@ -49,3 +49,10 @@ string getAnArrayContent() {
   // Values stored at an unknown index
   result = "ArrayElement[?]"
 }
+
+/**
+ * Gets an argument position up to a certain limit.
+ *
+ * This can be used to generate flow summaries that should preserve such positions.
+ */
+int getAnArgumentPosition() { result = [0 .. 10] }

javascript/ql/lib/semmle/javascript/internal/flow_summaries/Promises.qll

@@ -368,3 +368,29 @@ private class PromiseWithResolversLike extends SummarizedCallable {
     )
   }
 }
+
+class PromiseTry extends DataFlow::SummarizedCallable {
+  PromiseTry() { this = "Promise.try()" }
+
+  override DataFlow::CallNode getACallSimple() {
+    result = promiseConstructorRef().getAMemberCall(["try", "attempt"])
+    or
+    result = DataFlow::moduleImport(["p-try", "es6-promise-try"]).getACall()
+  }
+
+  override predicate propagatesFlow(string input, string output, boolean preservesValue) {
+    preservesValue = true and
+    (
+      exists(int i | i = getAnArgumentPosition() |
+        input = "Argument[" + (i + 1) + "]" and
+        output = "Argument[0].Parameter[" + i + "]"
+      )
+      or
+      input = "Argument[0].ReturnValue" and
+      output = "ReturnValue.Awaited"
+      or
+      input = "Argument[0].ReturnValue[exception]" and
+      output = "ReturnValue.Awaited[error]"
+    )
+  }
+}

javascript/ql/src/change-notes/2025-09-16-promise-try-array-with.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Data flow is now tracked through the `Promise.try` and `Array.prototype.with` functions.

javascript/ql/test/library-tests/TripleDot/array-with.js

@@ -0,0 +1,25 @@
+function t1() {
+    const arr = [1, 2, 3];
+    const newArr = arr.with(1, source('with.1'));
+    sink(newArr[1]); // $ hasValueFlow=with.1
+}
+
+function t2() {
+    const arr = [source('with.2.1'), 2, source('with.2.3')];
+    const newArr = arr.with(1, 'replaced');
+    sink(newArr[0]); // $ hasValueFlow=with.2.1
+    sink(newArr[2]); // $ hasValueFlow=with.2.3
+}
+
+function t3() {
+    const arr = [1, 2, 3];
+    const index = source('with.3.index');
+    const newArr = arr.with(index, 'new value');
+    // No assertions here as the index is tainted, not the value
+}
+
+function t4() {
+    const arr = [1, 2, 3];
+    const newArr = arr.with(1, source('with.4'));
+    sink(arr[1]); // This should NOT have value flow as with() returns a new array
+}

javascript/ql/test/library-tests/TripleDot/promise-try.js

@@ -0,0 +1,29 @@
+async function t1() {
+    const promise = Promise.try(() => {
+        return source('try.1');
+    });
+    sink(await promise); // $ hasValueFlow=try.1
+}
+
+async function t2() {
+    const promise = Promise.try((x) => {
+        return x
+    }, source('try.2'));
+    sink(await promise); // $ hasValueFlow=try.2
+}
+
+async function t3() {
+    const promise = Promise.try((x) => {
+        throw x;
+    }, source('try.3'));
+    promise.catch(err => {
+        sink(err); // $ hasValueFlow=try.3
+    });
+}
+
+async function t4() {
+    const promise = Promise.try((x, y) => {
+        return y;
+    }, source('try.4.1'), source('try.4.2'));
+    sink(await promise); //  $ hasValueFlow=try.4.2
+}