Special case emitting undefined[] for empty arrays.

palantir · Apr 7, 2019 · 9054ba1 · 9054ba1
1 parent 00b4a5d
commit 9054ba1
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Showing 2 changed files with 15 additions and 6 deletions.
diff --git a/src/rules/restrictPlusOperandsRule.ts b/src/rules/restrictPlusOperandsRule.ts
@@ -52,7 +52,7 @@ function walk(ctx: Lint.WalkContext, tc: ts.TypeChecker) {
             const rightType = tc.getTypeAtLocation(node.right);
             const rightTypeStr = getBaseTypeOfLiteralType(rightType);
             if (leftTypeStr === "invalid" || rightTypeStr === "invalid" || leftTypeStr !== rightTypeStr) {
-                const actualTypes = `, but found ${tc.typeToString(leftType, node)} + ${tc.typeToString(rightType, node)}`;
+                const actualTypes = `, but found ${getTypeString(tc, node.left, leftType)} + ${getTypeString(tc, node.right, rightType)}`;
                 let message = Rule.INVALID_TYPES_ERROR + actualTypes;
                 if (leftTypeStr === "string" || rightTypeStr === "string") {
                     message += Rule.SUGGEST_TEMPLATE_LITERALS;
@@ -64,6 +64,15 @@ function walk(ctx: Lint.WalkContext, tc: ts.TypeChecker) {
     });
 }
 
+function getTypeString(tc: ts.TypeChecker, node: ts.Node, type: ts.Type) {
+    const typeString = tc.typeToString(type, node);
+    if (typeString === "undefined[]" && ts.isArrayLiteralExpression(node) && !node.elements.length) {
+        // Special case literal "[]" arrays that would otherwise be emitted as undefined[].
+        return "[]";
+    }
+    return typeString;
+}
+
 function getBaseTypeOfLiteralType(type: ts.Type): "string" | "number" | "invalid" {
     if (
         isTypeFlagSet(type, ts.TypeFlags.StringLiteral) ||

diff --git a/test/rules/restrict-plus-operands/test.ts.lint b/test/rules/restrict-plus-operands/test.ts.lint
@@ -19,13 +19,13 @@ var pair: NumberStringPair = {
 var bad1  = 5 + "10";
             ~~~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found 5 + "10". Consider using template literals.]
 var bad2  = [] + 5;
-            ~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found undefined[] + 5]
+            ~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found [] + 5]
 var bad3  = [] + {};
-            ~~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found undefined[] + {}]
+            ~~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found [] + {}]
 var bad4  = [] + [];
-            ~~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found undefined[] + undefined[]]
+            ~~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found [] + []]
 var bad4  = 5 + [];
-            ~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found 5 + undefined[]]
+            ~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found 5 + []]
 var bad5  = "5" + {};
             ~~~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found "5" + {}. Consider using template literals.]
 var bad6  = 5.5 + "5";
@@ -39,7 +39,7 @@ var bad9  = y + x;
 var bad10 = x + {};
             ~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found number + {}]
 var bad11 = [] + y;
-            ~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found undefined[] + string. Consider using template literals.]
+            ~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found [] + string. Consider using template literals.]
 var bad12 = pair.first + "10";
             ~~~~~~~~~~~~~~~~~  [Operands of '+' operation must either be both strings or both numbers, but found number + "10". Consider using template literals.]
 var bad13 = 5 + pair.second;