Omit tostring from template literal spans if they are strings (TypeScriptToLua#948)

hazzard993 · web-flow · commit 5ced4c74ff5f · 2020-12-21T12:51:27.000+01:00
* Omit tostring from template literal spans if they are a definite string type

* Add negative tests

* Simplify and split templateLiteral tests
diff --git a/src/transformation/visitors/template.ts b/src/transformation/visitors/template.ts
@@ -3,6 +3,7 @@ import * as lua from "../../LuaAST";
 import { FunctionVisitor } from "../context";
 import { ContextType, getDeclarationContextType } from "../utils/function-context";
 import { wrapInToStringForConcat } from "../utils/lua-ast";
+import { isStringType } from "../utils/typescript/types";
 import { transformArguments, transformContextualCallExpression } from "./call";
 
 // TODO: Source positions
@@ -25,7 +26,12 @@ export const transformTemplateExpression: FunctionVisitor<ts.TemplateExpression>
 
     for (const span of node.templateSpans) {
         const expression = context.transformExpression(span.expression);
-        parts.push(wrapInToStringForConcat(expression));
+        const spanType = context.checker.getTypeAtLocation(span.expression);
+        if (isStringType(context, spanType)) {
+            parts.push(expression);
+        } else {
+            parts.push(wrapInToStringForConcat(expression));
+        }
 
         const text = span.literal.text;
         if (text.length > 0) {
diff --git a/test/unit/templateLiterals.spec.ts b/test/unit/templateLiterals.spec.ts
@@ -60,3 +60,26 @@ test.each(["func`noSelfParameter`", "obj.func`noSelfParameter`", "obj[`func`]`no
         `.expectToMatchJsResult();
     }
 );
+
+test.each(["number", "string | any"])("template span expect tostring for non string type (%p)", type => {
+    util.testFunction`
+        // @ts-ignore
+        const msg = "" as ${type};
+        return \`\${msg}\`;
+    `
+        .tap(builder => expect(builder.getMainLuaCodeChunk()).toContain("tostring"))
+        .expectToMatchJsResult();
+});
+
+test.each(["string", "'string literal type'", "string & unknown"])(
+    "template span expect no tostring for string-like type (%p)",
+    type => {
+        util.testFunction`
+            // @ts-ignore
+            const msg = "" as ${type};
+            return \`\${msg}\`;
+        `
+            .tap(builder => expect(builder.getMainLuaCodeChunk()).not.toContain("tostring"))
+            .expectToMatchJsResult();
+    }
+);
