Check for symbol types in template expressions

Author: jack-williams

src/compiler/checker.ts

@@ -19361,7 +19361,9 @@ namespace ts {
             // A place where we actually *are* concerned with the expressions' types are
             // in tagged templates.
             forEach(node.templateSpans, templateSpan => {
-                checkExpression(templateSpan.expression);
+                if (maybeTypeOfKind(checkExpression(templateSpan.expression), TypeFlags.ESSymbolLike)) {
+                    error(templateSpan.expression, Diagnostics.Type_0_cannot_be_converted_to_type_1, typeToString(esSymbolType), typeToString(stringType));
+                }
             });
 
             return stringType;

tests/baselines/reference/noImplicitSymbolToString.errors.txt

@@ -0,0 +1,21 @@
+tests/cases/compiler/noImplicitSymbolToString.ts(6,30): error TS2352: Type 'symbol' cannot be converted to type 'string'.
+tests/cases/compiler/noImplicitSymbolToString.ts(7,30): error TS2469: The '+' operator cannot be applied to type 'symbol'.
+tests/cases/compiler/noImplicitSymbolToString.ts(8,8): error TS2469: The '+=' operator cannot be applied to type 'symbol'.
+
+
+==== tests/cases/compiler/noImplicitSymbolToString.ts (3 errors) ====
+    // Fix #19666
+    
+    let symbol!: symbol;
+    let str = "hello ";
+    
+    const templateStr = `hello ${symbol}`;
+                                 ~~~~~~
+!!! error TS2352: Type 'symbol' cannot be converted to type 'string'.
+    const appendStr = "hello " + symbol;
+                                 ~~~~~~
+!!! error TS2469: The '+' operator cannot be applied to type 'symbol'.
+    str += symbol;
+           ~~~~~~
+!!! error TS2469: The '+=' operator cannot be applied to type 'symbol'.
+    

tests/baselines/reference/noImplicitSymbolToString.js

@@ -0,0 +1,18 @@
+//// [noImplicitSymbolToString.ts]
+// Fix #19666
+
+let symbol!: symbol;
+let str = "hello ";
+
+const templateStr = `hello ${symbol}`;
+const appendStr = "hello " + symbol;
+str += symbol;
+
+
+//// [noImplicitSymbolToString.js]
+// Fix #19666
+var symbol;
+var str = "hello ";
+var templateStr = "hello " + symbol;
+var appendStr = "hello " + symbol;
+str += symbol;

tests/baselines/reference/noImplicitSymbolToString.symbols

@@ -0,0 +1,21 @@
+=== tests/cases/compiler/noImplicitSymbolToString.ts ===
+// Fix #19666
+
+let symbol!: symbol;
+>symbol : Symbol(symbol, Decl(noImplicitSymbolToString.ts, 2, 3))
+
+let str = "hello ";
+>str : Symbol(str, Decl(noImplicitSymbolToString.ts, 3, 3))
+
+const templateStr = `hello ${symbol}`;
+>templateStr : Symbol(templateStr, Decl(noImplicitSymbolToString.ts, 5, 5))
+>symbol : Symbol(symbol, Decl(noImplicitSymbolToString.ts, 2, 3))
+
+const appendStr = "hello " + symbol;
+>appendStr : Symbol(appendStr, Decl(noImplicitSymbolToString.ts, 6, 5))
+>symbol : Symbol(symbol, Decl(noImplicitSymbolToString.ts, 2, 3))
+
+str += symbol;
+>str : Symbol(str, Decl(noImplicitSymbolToString.ts, 3, 3))
+>symbol : Symbol(symbol, Decl(noImplicitSymbolToString.ts, 2, 3))
+

tests/baselines/reference/noImplicitSymbolToString.types

@@ -0,0 +1,26 @@
+=== tests/cases/compiler/noImplicitSymbolToString.ts ===
+// Fix #19666
+
+let symbol!: symbol;
+>symbol : symbol
+
+let str = "hello ";
+>str : string
+>"hello " : "hello "
+
+const templateStr = `hello ${symbol}`;
+>templateStr : string
+>`hello ${symbol}` : string
+>symbol : symbol
+
+const appendStr = "hello " + symbol;
+>appendStr : string
+>"hello " + symbol : string
+>"hello " : "hello "
+>symbol : symbol
+
+str += symbol;
+>str += symbol : string
+>str : string
+>symbol : symbol
+

tests/cases/compiler/noImplicitSymbolToString.ts

@@ -0,0 +1,8 @@
+// Fix #19666
+
+let symbol!: symbol;
+let str = "hello ";
+
+const templateStr = `hello ${symbol}`;
+const appendStr = "hello " + symbol;
+str += symbol;