Omit empty template tail literals.

Author: DanielRosenwasser

src/compiler/emitter.ts

@@ -852,8 +852,13 @@ module ts {
                         write(")");
                     }
 
-                    write(" + ")
-                    emitLiteral(templateSpan.literal);
+                    // Only emit if the literal is non-empty.
+                    // The binary '+' operator is left-associative, so the first string concatenation will force
+                    // the result up to this point to be a string. Emitting a '+ ""' has no semantic effect.
+                    if (templateSpan.literal.text.length !== 0) {
+                        write(" + ")
+                        emitLiteral(templateSpan.literal);
+                    }
                 });
 
                 if (templateNeedsParens) {

tests/baselines/reference/templateStringInInOperator.js

@@ -2,4 +2,4 @@
 var x = `${ "hi" }` in { hi: 10, hello: 20};
 
 //// [templateStringInInOperator.js]
-var x = "" + "hi" + "" in { hi: 10, hello: 20 };
+var x = "" + "hi" in { hi: 10, hello: 20 };

tests/baselines/reference/templateStringWithEmptyLiteralPortions.js

@@ -0,0 +1,38 @@
+//// [templateStringWithEmptyLiteralPortions.ts]
+var a = ``;
+
+var b = `${ 0 }`;
+
+var c = `1${ 0 }`;
+
+var d = `${ 0 }2`;
+
+var e = `1${ 0 }2`;
+
+var f = `${ 0 }${ 0 }`;
+
+var g = `1${ 0 }${ 0 }`;
+
+var h = `${ 0 }2${ 0 }`;
+
+var i = `1${ 0 }2${ 0 }`;
+
+var j = `${ 0 }${ 0 }3`;
+
+var k = `1${ 0 }${ 0 }3`;
+
+var l = `1${ 0 }2${ 0 }3`;
+
+//// [templateStringWithEmptyLiteralPortions.js]
+var a = "";
+var b = "" + 0;
+var c = "1" + 0;
+var d = "" + 0 + "2";
+var e = "1" + 0 + "2";
+var f = "" + 0 + 0;
+var g = "1" + 0 + 0;
+var h = "" + 0 + "2" + 0;
+var i = "1" + 0 + "2" + 0;
+var j = "" + 0 + 0 + "3";
+var k = "1" + 0 + 0 + "3";
+var l = "1" + 0 + "2" + 0 + "3";

tests/baselines/reference/templateStringWithEmptyLiteralPortions.types

@@ -0,0 +1,37 @@
+=== tests/cases/conformance/es6/templates/templateStringWithEmptyLiteralPortions.ts ===
+var a = ``;
+>a : string
+
+var b = `${ 0 }`;
+>b : string
+
+var c = `1${ 0 }`;
+>c : string
+
+var d = `${ 0 }2`;
+>d : string
+
+var e = `1${ 0 }2`;
+>e : string
+
+var f = `${ 0 }${ 0 }`;
+>f : string
+
+var g = `1${ 0 }${ 0 }`;
+>g : string
+
+var h = `${ 0 }2${ 0 }`;
+>h : string
+
+var i = `1${ 0 }2${ 0 }`;
+>i : string
+
+var j = `${ 0 }${ 0 }3`;
+>j : string
+
+var k = `1${ 0 }${ 0 }3`;
+>k : string
+
+var l = `1${ 0 }2${ 0 }3`;
+>l : string
+

tests/baselines/reference/templateStringWithEmptyLiteralPortionsES6.js

@@ -0,0 +1,38 @@
+//// [templateStringWithEmptyLiteralPortionsES6.ts]
+var a = ``;
+
+var b = `${ 0 }`;
+
+var c = `1${ 0 }`;
+
+var d = `${ 0 }2`;
+
+var e = `1${ 0 }2`;
+
+var f = `${ 0 }${ 0 }`;
+
+var g = `1${ 0 }${ 0 }`;
+
+var h = `${ 0 }2${ 0 }`;
+
+var i = `1${ 0 }2${ 0 }`;
+
+var j = `${ 0 }${ 0 }3`;
+
+var k = `1${ 0 }${ 0 }3`;
+
+var l = `1${ 0 }2${ 0 }3`;
+
+//// [templateStringWithEmptyLiteralPortionsES6.js]
+var a = ``;
+var b = `${0}`;
+var c = `1${0}`;
+var d = `${0}2`;
+var e = `1${0}2`;
+var f = `${0}${0}`;
+var g = `1${0}${0}`;
+var h = `${0}2${0}`;
+var i = `1${0}2${0}`;
+var j = `${0}${0}3`;
+var k = `1${0}${0}3`;
+var l = `1${0}2${0}3`;

tests/baselines/reference/templateStringWithEmptyLiteralPortionsES6.types

@@ -0,0 +1,37 @@
+=== tests/cases/conformance/es6/templates/templateStringWithEmptyLiteralPortionsES6.ts ===
+var a = ``;
+>a : string
+
+var b = `${ 0 }`;
+>b : string
+
+var c = `1${ 0 }`;
+>c : string
+
+var d = `${ 0 }2`;
+>d : string
+
+var e = `1${ 0 }2`;
+>e : string
+
+var f = `${ 0 }${ 0 }`;
+>f : string
+
+var g = `1${ 0 }${ 0 }`;
+>g : string
+
+var h = `${ 0 }2${ 0 }`;
+>h : string
+
+var i = `1${ 0 }2${ 0 }`;
+>i : string
+
+var j = `${ 0 }${ 0 }3`;
+>j : string
+
+var k = `1${ 0 }${ 0 }3`;
+>k : string
+
+var l = `1${ 0 }2${ 0 }3`;
+>l : string
+

tests/cases/conformance/es6/templates/templateStringWithEmptyLiteralPortions.ts

@@ -0,0 +1,23 @@
+var a = ``;
+
+var b = `${ 0 }`;
+
+var c = `1${ 0 }`;
+
+var d = `${ 0 }2`;
+
+var e = `1${ 0 }2`;
+
+var f = `${ 0 }${ 0 }`;
+
+var g = `1${ 0 }${ 0 }`;
+
+var h = `${ 0 }2${ 0 }`;
+
+var i = `1${ 0 }2${ 0 }`;
+
+var j = `${ 0 }${ 0 }3`;
+
+var k = `1${ 0 }${ 0 }3`;
+
+var l = `1${ 0 }2${ 0 }3`;

tests/cases/conformance/es6/templates/templateStringWithEmptyLiteralPortionsES6.ts

@@ -0,0 +1,24 @@
+// @target: ES6
+var a = ``;
+
+var b = `${ 0 }`;
+
+var c = `1${ 0 }`;
+
+var d = `${ 0 }2`;
+
+var e = `1${ 0 }2`;
+
+var f = `${ 0 }${ 0 }`;
+
+var g = `1${ 0 }${ 0 }`;
+
+var h = `${ 0 }2${ 0 }`;
+
+var i = `1${ 0 }2${ 0 }`;
+
+var j = `${ 0 }${ 0 }3`;
+
+var k = `1${ 0 }${ 0 }3`;
+
+var l = `1${ 0 }2${ 0 }3`;