From fc08ff5a36cd48a7b619f8c37dd42e3fa89389af Mon Sep 17 00:00:00 2001
From: Jack Williams <jw@jackw.io>
Date: Thu, 1 Mar 2018 03:07:53 +0000
Subject: [PATCH] Check for symbol types in template expressions

---
 src/compiler/checker.ts                       |  4 ++-
 .../noImplicitSymbolToString.errors.txt       | 21 +++++++++++++++
 .../reference/noImplicitSymbolToString.js     | 18 +++++++++++++
 .../noImplicitSymbolToString.symbols          | 21 +++++++++++++++
 .../reference/noImplicitSymbolToString.types  | 26 +++++++++++++++++++
 .../compiler/noImplicitSymbolToString.ts      |  8 ++++++
 6 files changed, 97 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/noImplicitSymbolToString.errors.txt
 create mode 100644 tests/baselines/reference/noImplicitSymbolToString.js
 create mode 100644 tests/baselines/reference/noImplicitSymbolToString.symbols
 create mode 100644 tests/baselines/reference/noImplicitSymbolToString.types
 create mode 100644 tests/cases/compiler/noImplicitSymbolToString.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 9579ba80d0f..19e5e2a880c 100644
--- a/src/compiler/checker.ts
+++ b/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;
diff --git a/tests/baselines/reference/noImplicitSymbolToString.errors.txt b/tests/baselines/reference/noImplicitSymbolToString.errors.txt
new file mode 100644
index 00000000000..43f5bb88864
--- /dev/null
+++ b/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'.
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/noImplicitSymbolToString.js b/tests/baselines/reference/noImplicitSymbolToString.js
new file mode 100644
index 00000000000..c7e62c7a86e
--- /dev/null
+++ b/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;
diff --git a/tests/baselines/reference/noImplicitSymbolToString.symbols b/tests/baselines/reference/noImplicitSymbolToString.symbols
new file mode 100644
index 00000000000..a043aecefb1
--- /dev/null
+++ b/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))
+
diff --git a/tests/baselines/reference/noImplicitSymbolToString.types b/tests/baselines/reference/noImplicitSymbolToString.types
new file mode 100644
index 00000000000..45a69c5e950
--- /dev/null
+++ b/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
+
diff --git a/tests/cases/compiler/noImplicitSymbolToString.ts b/tests/cases/compiler/noImplicitSymbolToString.ts
new file mode 100644
index 00000000000..5340e2cd972
--- /dev/null
+++ b/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;