TypeScript: Support type arguments on tagged templates (#7754)

| Q                        | A
| ------------------------ | ---
| Fixed Issues?            | #7747 (partly)
| Patch: Bug Fix?          | 
| Major: Breaking Change?  | 
| Minor: New Feature?      | Yes
| Tests Added + Pass?      | Yes
| Documentation PR         |
| Any Dependency Changes?  |
| License                  | MIT

@JamesHenry This changes the AST format. CC @DanielRosenwasser for review.
Supports parsing type arguments on tagged template calls.
Should wait on Microsoft/TypeScript#23430 to be merged so we're sure we have the final syntax.

packages/babel-generator/src/generators/template-literals.js

@@ -1,5 +1,6 @@
 export function TaggedTemplateExpression(node: Object) {
   this.print(node.tag, node);
+  this.print(node.typeParameters, node); // TS
   this.print(node.quasi, node);
 }
 

packages/babel-generator/test/fixtures/typescript/type-arguments-tagged-template/input.js

@@ -0,0 +1 @@
+f<T>``;

packages/babel-generator/test/fixtures/typescript/type-arguments-tagged-template/output.js

@@ -0,0 +1 @@
+f<T>``;

packages/babel-parser/src/parser/expression.js

@@ -563,9 +563,32 @@ export default class ExpressionParser extends LValParser {
       }
       return node;
     } else if (this.match(tt.backQuote)) {
-      const node = this.startNodeAt(startPos, startLoc);
+      return this.parseTaggedTemplateExpression(
+        startPos,
+        startLoc,
+        base,
+        state,
+      );
+    } else {
+      state.stop = true;
+      return base;
+    }
+  }
+
+  parseTaggedTemplateExpression(
+    startPos: number,
+    startLoc: Position,
+    base: N.Expression,
+    state: N.ParseSubscriptState,
+    typeArguments?: ?N.TsTypeParameterInstantiation,
+  ): N.TaggedTemplateExpression {
+    const node: N.TaggedTemplateExpression = this.startNodeAt(
+      startPos,
+      startLoc,
+    );
     node.tag = base;
     node.quasi = this.parseTemplate(true);
+    if (typeArguments) node.typeParameters = typeArguments;
     if (state.optionalChainMember) {
       this.raise(
         startPos,
@@ -573,10 +596,6 @@ export default class ExpressionParser extends LValParser {
       );
     }
     return this.finishNode(node, "TaggedTemplateExpression");
-    } else {
-      state.stop = true;
-      return base;
-    }
   }
 
   atPossibleAsync(base: N.Expression): boolean {

packages/babel-parser/src/plugins/typescript.js

@@ -836,16 +836,6 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return this.finishNode(node, "TSTypeAssertion");
     }
 
-    tsTryParseTypeArgumentsInExpression(
-      eatNextToken: boolean,
-    ): ?N.TsTypeParameterInstantiation {
-      return this.tsTryParseAndCatch(() => {
-        const res = this.tsParseTypeArguments();
-        if (eatNextToken) this.expect(tt.parenL);
-        return res;
-      });
-    }
-
     tsParseHeritageClause(): $ReadOnlyArray<N.TsExpressionWithTypeArguments> {
       return this.tsParseDelimitedList(
         "HeritageClauseElement",
@@ -1376,8 +1366,11 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         return this.finishNode(nonNullExpression, "TSNonNullExpression");
       }
 
-      if (!noCalls && this.isRelational("<")) {
+      // There are number of things we are going to "maybe" parse, like type arguments on
-        if (this.atPossibleAsync(base)) {
+      // tagged template expressions. If any of them fail, walk it back and continue.
+      const result = this.tsTryParseAndCatch(() => {
+        if (this.isRelational("<")) {
+          if (!noCalls && this.atPossibleAsync(base)) {
             // Almost certainly this is a generic async function `async <T>() => ...
             // But it might be a call with a type argument `async<T>();`
             const asyncArrowFn = this.tsTryParseGenericAsyncArrowFunction(
@@ -1392,12 +1385,10 @@ export default (superClass: Class<Parser>): Class<Parser> =>
           const node: N.CallExpression = this.startNodeAt(startPos, startLoc);
           node.callee = base;
 
-        // May be passing type arguments. But may just be the `<` operator.
+          const typeArguments = this.tsParseTypeArguments();
-        // Note: With `/*eatNextToken*/ true` this also eats the `(` following the type arguments
+
-        const typeArguments = this.tsTryParseTypeArgumentsInExpression(
-          /*eatNextToken*/ true,
-        );
           if (typeArguments) {
+            if (!noCalls && this.eat(tt.parenL)) {
               // possibleAsync always false here, because we would have handled it above.
               // $FlowIgnore (won't be any undefined arguments)
               node.arguments = this.parseCallExpressionArguments(
@@ -1406,8 +1397,22 @@ export default (superClass: Class<Parser>): Class<Parser> =>
               );
               node.typeParameters = typeArguments;
               return this.finishCallExpression(node);
+            } else if (this.match(tt.backQuote)) {
+              return this.parseTaggedTemplateExpression(
+                startPos,
+                startLoc,
+                base,
+                state,
+                typeArguments,
+              );
             }
           }
+        }
+
+        this.unexpected();
+      });
+
+      if (result) return result;
 
       return super.parseSubscript(base, startPos, startLoc, noCalls, state);
     }
@@ -2127,8 +2132,8 @@ export default (superClass: Class<Parser>): Class<Parser> =>
     jsxParseOpeningElementAfterName(
       node: N.JSXOpeningElement,
     ): N.JSXOpeningElement {
-      const typeArguments = this.tsTryParseTypeArgumentsInExpression(
+      const typeArguments = this.tsTryParseAndCatch(() =>
-        /*eatNextToken*/ false,
+        this.tsParseTypeArguments(),
       );
       if (typeArguments) node.typeParameters = typeArguments;
       return super.jsxParseOpeningElementAfterName(node);

packages/babel-parser/src/types.js

@@ -577,6 +577,7 @@ export type TaggedTemplateExpression = NodeBase & {
   type: "TaggedTemplateExpression",
   tag: Expression,
   quasi: TemplateLiteral,
+  typeParameters?: ?TypeParameterInstantiationBase, // TODO: Not in spec
 };
 
 export type TemplateElement = NodeBase & {

packages/babel-parser/test/fixtures/typescript/type-arguments/tagged-template-no-asi/input.js

@@ -0,0 +1,2 @@
+new C<T>
+``

packages/babel-parser/test/fixtures/typescript/type-arguments/tagged-template-no-asi/output.json

@@ -0,0 +1,185 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 11,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 2,
+      "column": 2
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 11,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 2,
+        "column": 2
+      }
+    },
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 11,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 2,
+            "column": 2
+          }
+        },
+        "expression": {
+          "type": "NewExpression",
+          "start": 0,
+          "end": 11,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 2,
+              "column": 2
+            }
+          },
+          "callee": {
+            "type": "TaggedTemplateExpression",
+            "start": 4,
+            "end": 11,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 4
+              },
+              "end": {
+                "line": 2,
+                "column": 2
+              }
+            },
+            "tag": {
+              "type": "Identifier",
+              "start": 4,
+              "end": 5,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 4
+                },
+                "end": {
+                  "line": 1,
+                  "column": 5
+                },
+                "identifierName": "C"
+              },
+              "name": "C"
+            },
+            "quasi": {
+              "type": "TemplateLiteral",
+              "start": 9,
+              "end": 11,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 0
+                },
+                "end": {
+                  "line": 2,
+                  "column": 2
+                }
+              },
+              "expressions": [],
+              "quasis": [
+                {
+                  "type": "TemplateElement",
+                  "start": 10,
+                  "end": 10,
+                  "loc": {
+                    "start": {
+                      "line": 2,
+                      "column": 1
+                    },
+                    "end": {
+                      "line": 2,
+                      "column": 1
+                    }
+                  },
+                  "value": {
+                    "raw": "",
+                    "cooked": ""
+                  },
+                  "tail": true
+                }
+              ]
+            },
+            "typeParameters": {
+              "type": "TSTypeParameterInstantiation",
+              "start": 5,
+              "end": 8,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 5
+                },
+                "end": {
+                  "line": 1,
+                  "column": 8
+                }
+              },
+              "params": [
+                {
+                  "type": "TSTypeReference",
+                  "start": 6,
+                  "end": 7,
+                  "loc": {
+                    "start": {
+                      "line": 1,
+                      "column": 6
+                    },
+                    "end": {
+                      "line": 1,
+                      "column": 7
+                    }
+                  },
+                  "typeName": {
+                    "type": "Identifier",
+                    "start": 6,
+                    "end": 7,
+                    "loc": {
+                      "start": {
+                        "line": 1,
+                        "column": 6
+                      },
+                      "end": {
+                        "line": 1,
+                        "column": 7
+                      },
+                      "identifierName": "T"
+                    },
+                    "name": "T"
+                  }
+                }
+              ]
+            }
+          },
+          "arguments": []
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/typescript/type-arguments/tagged-template/input.js

@@ -0,0 +1 @@
+f<T>``;

packages/babel-parser/test/fixtures/typescript/type-arguments/tagged-template/output.json

@@ -0,0 +1,169 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 7,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 7
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 7,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 7
+      }
+    },
+    "sourceType": "module",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 7,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 7
+          }
+        },
+        "expression": {
+          "type": "TaggedTemplateExpression",
+          "start": 0,
+          "end": 6,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 6
+            }
+          },
+          "tag": {
+            "type": "Identifier",
+            "start": 0,
+            "end": 1,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 0
+              },
+              "end": {
+                "line": 1,
+                "column": 1
+              },
+              "identifierName": "f"
+            },
+            "name": "f"
+          },
+          "quasi": {
+            "type": "TemplateLiteral",
+            "start": 4,
+            "end": 6,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 4
+              },
+              "end": {
+                "line": 1,
+                "column": 6
+              }
+            },
+            "expressions": [],
+            "quasis": [
+              {
+                "type": "TemplateElement",
+                "start": 5,
+                "end": 5,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 5
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 5
+                  }
+                },
+                "value": {
+                  "raw": "",
+                  "cooked": ""
+                },
+                "tail": true
+              }
+            ]
+          },
+          "typeParameters": {
+            "type": "TSTypeParameterInstantiation",
+            "start": 1,
+            "end": 4,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 1
+              },
+              "end": {
+                "line": 1,
+                "column": 4
+              }
+            },
+            "params": [
+              {
+                "type": "TSTypeReference",
+                "start": 2,
+                "end": 3,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 2
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 3
+                  }
+                },
+                "typeName": {
+                  "type": "Identifier",
+                  "start": 2,
+                  "end": 3,
+                  "loc": {
+                    "start": {
+                      "line": 1,
+                      "column": 2
+                    },
+                    "end": {
+                      "line": 1,
+                      "column": 3
+                    },
+                    "identifierName": "T"
+                  },
+                  "name": "T"
+                }
+              }
+            ]
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-plugin-transform-typescript/src/index.js

@@ -268,6 +268,10 @@ export default declare((api, { jsxPragma = "React" }) => {
       JSXOpeningElement(path) {
         path.node.typeParameters = null;
       },
+
+      TaggedTemplateExpression(path) {
+        path.node.typeParameters = null;
+      },
     },
   };
 

packages/babel-plugin-transform-typescript/test/fixtures/type-arguments/tagged-template/input.js

@@ -0,0 +1 @@
+f<T>``;

packages/babel-plugin-transform-typescript/test/fixtures/type-arguments/tagged-template/output.js

@@ -0,0 +1 @@
+f``;

packages/babel-types/src/definitions/es2015.js

@@ -510,6 +510,13 @@ defineType("TaggedTemplateExpression", {
     quasi: {
       validate: assertNodeType("TemplateLiteral"),
     },
+    typeParameters: {
+      validate: assertNodeType(
+        "TypeParameterInstantiation",
+        "TSTypeParameterInstantiation",
+      ),
+      optional: true,
+    },
   },
 });