From 6dde1621cb0f113d4a2006fa17861e2c19661405 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wwigham@gmail.com>
Date: Wed, 21 Oct 2020 12:31:29 -0700
Subject: [PATCH] Track control flow for comma expressions in call expressions

---
 src/compiler/binder.ts                        |  1 +
 src/compiler/checker.ts                       |  3 +-
 .../controlFlowCommaExpressionFunctionCall.js | 23 +++++++++++++
 ...rolFlowCommaExpressionFunctionCall.symbols | 25 ++++++++++++++
 ...ntrolFlowCommaExpressionFunctionCall.types | 33 +++++++++++++++++++
 .../controlFlowCommaExpressionFunctionCall.ts | 11 +++++++
 6 files changed, 95 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/controlFlowCommaExpressionFunctionCall.js
 create mode 100644 tests/baselines/reference/controlFlowCommaExpressionFunctionCall.symbols
 create mode 100644 tests/baselines/reference/controlFlowCommaExpressionFunctionCall.types
 create mode 100644 tests/cases/compiler/controlFlowCommaExpressionFunctionCall.ts

diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
index 5e7695ffef366..9fcb5d09a4349 100644
--- a/src/compiler/binder.ts
+++ b/src/compiler/binder.ts
@@ -858,6 +858,7 @@ namespace ts {
         function isNarrowableReference(expr: Expression): boolean {
             return expr.kind === SyntaxKind.Identifier || expr.kind === SyntaxKind.PrivateIdentifier || expr.kind === SyntaxKind.ThisKeyword || expr.kind === SyntaxKind.SuperKeyword ||
                 (isPropertyAccessExpression(expr) || isNonNullExpression(expr) || isParenthesizedExpression(expr)) && isNarrowableReference(expr.expression) ||
+                isBinaryExpression(expr) && expr.operatorToken.kind === SyntaxKind.CommaToken && isNarrowableReference(expr.right) ||
                 isElementAccessExpression(expr) && isStringOrNumericLiteralLike(expr.argumentExpression) && isNarrowableReference(expr.expression) ||
                 isAssignmentExpression(expr) && isNarrowableReference(expr.left);
         }
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 601948a3ea08d..feb8ccd636466 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -20720,7 +20720,8 @@ namespace ts {
                 case SyntaxKind.NonNullExpression:
                     return isMatchingReference(source, (target as NonNullExpression | ParenthesizedExpression).expression);
                 case SyntaxKind.BinaryExpression:
-                    return isAssignmentExpression(target) && isMatchingReference(source, target.left);
+                    return (isAssignmentExpression(target) && isMatchingReference(source, target.left)) ||
+                        (isBinaryExpression(target) && target.operatorToken.kind === SyntaxKind.CommaToken && isMatchingReference(source, target.right));
             }
             switch (source.kind) {
                 case SyntaxKind.Identifier:
diff --git a/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.js b/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.js
new file mode 100644
index 0000000000000..c27f3ee472308
--- /dev/null
+++ b/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.js
@@ -0,0 +1,23 @@
+//// [controlFlowCommaExpressionFunctionCall.ts]
+const otherValue = () => true;
+const value : number | string = null as any;
+
+function isNumber(obj: any): obj is number {
+    return true; // method implementation irrelevant
+}
+
+// Bad case - fails
+if (isNumber((otherValue(), value))) {
+    const b = value; // string | number , but should be number
+}
+
+//// [controlFlowCommaExpressionFunctionCall.js]
+var otherValue = function () { return true; };
+var value = null;
+function isNumber(obj) {
+    return true; // method implementation irrelevant
+}
+// Bad case - fails
+if (isNumber((otherValue(), value))) {
+    var b = value; // string | number , but should be number
+}
diff --git a/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.symbols b/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.symbols
new file mode 100644
index 0000000000000..4372e3f1ebe2b
--- /dev/null
+++ b/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.symbols
@@ -0,0 +1,25 @@
+=== tests/cases/compiler/controlFlowCommaExpressionFunctionCall.ts ===
+const otherValue = () => true;
+>otherValue : Symbol(otherValue, Decl(controlFlowCommaExpressionFunctionCall.ts, 0, 5))
+
+const value : number | string = null as any;
+>value : Symbol(value, Decl(controlFlowCommaExpressionFunctionCall.ts, 1, 5))
+
+function isNumber(obj: any): obj is number {
+>isNumber : Symbol(isNumber, Decl(controlFlowCommaExpressionFunctionCall.ts, 1, 44))
+>obj : Symbol(obj, Decl(controlFlowCommaExpressionFunctionCall.ts, 3, 18))
+>obj : Symbol(obj, Decl(controlFlowCommaExpressionFunctionCall.ts, 3, 18))
+
+    return true; // method implementation irrelevant
+}
+
+// Bad case - fails
+if (isNumber((otherValue(), value))) {
+>isNumber : Symbol(isNumber, Decl(controlFlowCommaExpressionFunctionCall.ts, 1, 44))
+>otherValue : Symbol(otherValue, Decl(controlFlowCommaExpressionFunctionCall.ts, 0, 5))
+>value : Symbol(value, Decl(controlFlowCommaExpressionFunctionCall.ts, 1, 5))
+
+    const b = value; // string | number , but should be number
+>b : Symbol(b, Decl(controlFlowCommaExpressionFunctionCall.ts, 9, 9))
+>value : Symbol(value, Decl(controlFlowCommaExpressionFunctionCall.ts, 1, 5))
+}
diff --git a/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.types b/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.types
new file mode 100644
index 0000000000000..0464f85610247
--- /dev/null
+++ b/tests/baselines/reference/controlFlowCommaExpressionFunctionCall.types
@@ -0,0 +1,33 @@
+=== tests/cases/compiler/controlFlowCommaExpressionFunctionCall.ts ===
+const otherValue = () => true;
+>otherValue : () => boolean
+>() => true : () => boolean
+>true : true
+
+const value : number | string = null as any;
+>value : string | number
+>null as any : any
+>null : null
+
+function isNumber(obj: any): obj is number {
+>isNumber : (obj: any) => obj is number
+>obj : any
+
+    return true; // method implementation irrelevant
+>true : true
+}
+
+// Bad case - fails
+if (isNumber((otherValue(), value))) {
+>isNumber((otherValue(), value)) : boolean
+>isNumber : (obj: any) => obj is number
+>(otherValue(), value) : string | number
+>otherValue(), value : string | number
+>otherValue() : boolean
+>otherValue : () => boolean
+>value : string | number
+
+    const b = value; // string | number , but should be number
+>b : number
+>value : number
+}
diff --git a/tests/cases/compiler/controlFlowCommaExpressionFunctionCall.ts b/tests/cases/compiler/controlFlowCommaExpressionFunctionCall.ts
new file mode 100644
index 0000000000000..ff1d48c3ae783
--- /dev/null
+++ b/tests/cases/compiler/controlFlowCommaExpressionFunctionCall.ts
@@ -0,0 +1,11 @@
+const otherValue = () => true;
+const value : number | string = null as any;
+
+function isNumber(obj: any): obj is number {
+    return true; // method implementation irrelevant
+}
+
+// Bad case - fails
+if (isNumber((otherValue(), value))) {
+    const b = value; // string | number , but should be number
+}
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