From a38a58bad8b1482eff52df2235779b95421947c5 Mon Sep 17 00:00:00 2001
From: Sam Goldman <samgoldman@fb.com>
Date: Mon, 29 Feb 2016 17:20:55 -0800
Subject: [PATCH] Add support for Flow def-site variance syntax

This syntax allows you to specify whether a type variable can appear in
a covariant or contravariant position, and is super useful for, say,
Promise.

Right now this is hacked in jankily, but in the next major release we
should stop using Identifier nodes for type parameters.
---
 .../babel-generator/src/generators/types.js   |  10 +
 .../fixtures/flow/def-site-variance/actual.js |   3 +
 .../flow/def-site-variance/expected.js        |   3 +
 .../flow-comments/def-site-variance/actual.js |   3 +
 .../def-site-variance/expected.js             |   3 +
 .../strip-types/def-site-variance/actual.js   |   3 +
 .../strip-types/def-site-variance/expected.js |   2 +
 packages/babylon/src/plugins/flow.js          |  14 +
 .../flow/def-site-variance/1/actual.js        |   3 +
 .../flow/def-site-variance/1/expected.json    | 336 ++++++++++++++++++
 10 files changed, 380 insertions(+)
 create mode 100644 packages/babel-generator/test/fixtures/flow/def-site-variance/actual.js
 create mode 100644 packages/babel-generator/test/fixtures/flow/def-site-variance/expected.js
 create mode 100644 packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/actual.js
 create mode 100644 packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/expected.js
 create mode 100644 packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/actual.js
 create mode 100644 packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/expected.js
 create mode 100644 packages/babylon/test/fixtures/flow/def-site-variance/1/actual.js
 create mode 100644 packages/babylon/test/fixtures/flow/def-site-variance/1/expected.json

diff --git a/packages/babel-generator/src/generators/types.js b/packages/babel-generator/src/generators/types.js
index aed1c3f35c..6ca86a74e1 100644
--- a/packages/babel-generator/src/generators/types.js
+++ b/packages/babel-generator/src/generators/types.js
@@ -4,6 +4,16 @@
 import * as t from "babel-types";
 
 export function Identifier(node: Object) {
+  // FIXME: We hang variance off Identifer to support Flow's def-site variance.
+  // This is a terrible hack, but changing type annotations to use a new,
+  // dedicated node would be a breaking change. This should be cleaned up in
+  // the next major.
+  if (node.variance === "plus") {
+    this.push("+");
+  } else if (node.variance === "minus") {
+    this.push("-");
+  }
+
   this.push(node.name);
 }
 
diff --git a/packages/babel-generator/test/fixtures/flow/def-site-variance/actual.js b/packages/babel-generator/test/fixtures/flow/def-site-variance/actual.js
new file mode 100644
index 0000000000..f046505722
--- /dev/null
+++ b/packages/babel-generator/test/fixtures/flow/def-site-variance/actual.js
@@ -0,0 +1,3 @@
+class C<+T, -U> {}
+function f<+T, -U>() {}
+type T<+T, -U> = {};
diff --git a/packages/babel-generator/test/fixtures/flow/def-site-variance/expected.js b/packages/babel-generator/test/fixtures/flow/def-site-variance/expected.js
new file mode 100644
index 0000000000..f046505722
--- /dev/null
+++ b/packages/babel-generator/test/fixtures/flow/def-site-variance/expected.js
@@ -0,0 +1,3 @@
+class C<+T, -U> {}
+function f<+T, -U>() {}
+type T<+T, -U> = {};
diff --git a/packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/actual.js b/packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/actual.js
new file mode 100644
index 0000000000..f046505722
--- /dev/null
+++ b/packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/actual.js
@@ -0,0 +1,3 @@
+class C<+T, -U> {}
+function f<+T, -U>() {}
+type T<+T, -U> = {};
diff --git a/packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/expected.js b/packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/expected.js
new file mode 100644
index 0000000000..195209568b
--- /dev/null
+++ b/packages/babel-plugin-transform-flow-comments/test/fixtures/flow-comments/def-site-variance/expected.js
@@ -0,0 +1,3 @@
+class C /*:: <+T, -U>*/ {}
+function f /*:: <+T, -U>*/() {}
+/*:: type T<+T, -U> = {};*/
diff --git a/packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/actual.js b/packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/actual.js
new file mode 100644
index 0000000000..f046505722
--- /dev/null
+++ b/packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/actual.js
@@ -0,0 +1,3 @@
+class C<+T, -U> {}
+function f<+T, -U>() {}
+type T<+T, -U> = {};
diff --git a/packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/expected.js b/packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/expected.js
new file mode 100644
index 0000000000..9eb99a782f
--- /dev/null
+++ b/packages/babel-plugin-transform-flow-strip-types/test/fixtures/strip-types/def-site-variance/expected.js
@@ -0,0 +1,2 @@
+class C {}
+function f() {}
diff --git a/packages/babylon/src/plugins/flow.js b/packages/babylon/src/plugins/flow.js
index f856955176..3ecaeb84e2 100644
--- a/packages/babylon/src/plugins/flow.js
+++ b/packages/babylon/src/plugins/flow.js
@@ -624,9 +624,23 @@ pp.flowParseTypeAnnotation = function () {
 };
 
 pp.flowParseTypeAnnotatableIdentifier = function (requireTypeAnnotation, canBeOptionalParam) {
+  let variance;
+  if (this.match(tt.plusMin)) {
+    if (this.state.value === "+") {
+      variance = "plus";
+    } else if (this.state.value === "-") {
+      variance = "minus";
+    }
+    this.eat(tt.plusMin);
+  }
+
   let ident = this.parseIdentifier();
   let isOptionalParam = false;
 
+  if (variance) {
+    ident.variance = variance;
+  }
+
   if (canBeOptionalParam && this.eat(tt.question)) {
     this.expect(tt.question);
     isOptionalParam = true;
diff --git a/packages/babylon/test/fixtures/flow/def-site-variance/1/actual.js b/packages/babylon/test/fixtures/flow/def-site-variance/1/actual.js
new file mode 100644
index 0000000000..5eb19f458a
--- /dev/null
+++ b/packages/babylon/test/fixtures/flow/def-site-variance/1/actual.js
@@ -0,0 +1,3 @@
+class C<+T,-U> {}
+function f<+T,-U>() {}
+type T<+T,-U> = {}
diff --git a/packages/babylon/test/fixtures/flow/def-site-variance/1/expected.json b/packages/babylon/test/fixtures/flow/def-site-variance/1/expected.json
new file mode 100644
index 0000000000..b42edfb108
--- /dev/null
+++ b/packages/babylon/test/fixtures/flow/def-site-variance/1/expected.json
@@ -0,0 +1,336 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 59,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 3,
+      "column": 18
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 59,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 3,
+        "column": 18
+      }
+    },
+    "sourceType": "module",
+    "body": [
+      {
+        "type": "ClassDeclaration",
+        "start": 0,
+        "end": 17,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 17
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 6,
+          "end": 7,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 6
+            },
+            "end": {
+              "line": 1,
+              "column": 7
+            }
+          },
+          "name": "C"
+        },
+        "typeParameters": {
+          "type": "TypeParameterDeclaration",
+          "start": 7,
+          "end": 14,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 7
+            },
+            "end": {
+              "line": 1,
+              "column": 14
+            }
+          },
+          "params": [
+            {
+              "type": "Identifier",
+              "start": 9,
+              "end": 10,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 9
+                },
+                "end": {
+                  "line": 1,
+                  "column": 10
+                }
+              },
+              "name": "T",
+              "variance": "plus"
+            },
+            {
+              "type": "Identifier",
+              "start": 12,
+              "end": 13,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 12
+                },
+                "end": {
+                  "line": 1,
+                  "column": 13
+                }
+              },
+              "name": "U",
+              "variance": "minus"
+            }
+          ]
+        },
+        "superClass": null,
+        "body": {
+          "type": "ClassBody",
+          "start": 15,
+          "end": 17,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 15
+            },
+            "end": {
+              "line": 1,
+              "column": 17
+            }
+          },
+          "body": []
+        }
+      },
+      {
+        "type": "FunctionDeclaration",
+        "start": 18,
+        "end": 40,
+        "loc": {
+          "start": {
+            "line": 2,
+            "column": 0
+          },
+          "end": {
+            "line": 2,
+            "column": 22
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 27,
+          "end": 28,
+          "loc": {
+            "start": {
+              "line": 2,
+              "column": 9
+            },
+            "end": {
+              "line": 2,
+              "column": 10
+            }
+          },
+          "name": "f"
+        },
+        "generator": false,
+        "expression": false,
+        "async": false,
+        "typeParameters": {
+          "type": "TypeParameterDeclaration",
+          "start": 28,
+          "end": 35,
+          "loc": {
+            "start": {
+              "line": 2,
+              "column": 10
+            },
+            "end": {
+              "line": 2,
+              "column": 17
+            }
+          },
+          "params": [
+            {
+              "type": "Identifier",
+              "start": 30,
+              "end": 31,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 12
+                },
+                "end": {
+                  "line": 2,
+                  "column": 13
+                }
+              },
+              "name": "T",
+              "variance": "plus"
+            },
+            {
+              "type": "Identifier",
+              "start": 33,
+              "end": 34,
+              "loc": {
+                "start": {
+                  "line": 2,
+                  "column": 15
+                },
+                "end": {
+                  "line": 2,
+                  "column": 16
+                }
+              },
+              "name": "U",
+              "variance": "minus"
+            }
+          ]
+        },
+        "params": [],
+        "body": {
+          "type": "BlockStatement",
+          "start": 38,
+          "end": 40,
+          "loc": {
+            "start": {
+              "line": 2,
+              "column": 20
+            },
+            "end": {
+              "line": 2,
+              "column": 22
+            }
+          },
+          "body": [],
+          "directives": []
+        }
+      },
+      {
+        "type": "TypeAlias",
+        "start": 41,
+        "end": 59,
+        "loc": {
+          "start": {
+            "line": 3,
+            "column": 0
+          },
+          "end": {
+            "line": 3,
+            "column": 18
+          }
+        },
+        "id": {
+          "type": "Identifier",
+          "start": 46,
+          "end": 47,
+          "loc": {
+            "start": {
+              "line": 3,
+              "column": 5
+            },
+            "end": {
+              "line": 3,
+              "column": 6
+            }
+          },
+          "name": "T"
+        },
+        "typeParameters": {
+          "type": "TypeParameterDeclaration",
+          "start": 47,
+          "end": 54,
+          "loc": {
+            "start": {
+              "line": 3,
+              "column": 6
+            },
+            "end": {
+              "line": 3,
+              "column": 13
+            }
+          },
+          "params": [
+            {
+              "type": "Identifier",
+              "start": 49,
+              "end": 50,
+              "loc": {
+                "start": {
+                  "line": 3,
+                  "column": 8
+                },
+                "end": {
+                  "line": 3,
+                  "column": 9
+                }
+              },
+              "name": "T",
+              "variance": "plus"
+            },
+            {
+              "type": "Identifier",
+              "start": 52,
+              "end": 53,
+              "loc": {
+                "start": {
+                  "line": 3,
+                  "column": 11
+                },
+                "end": {
+                  "line": 3,
+                  "column": 12
+                }
+              },
+              "name": "U",
+              "variance": "minus"
+            }
+          ]
+        },
+        "right": {
+          "type": "ObjectTypeAnnotation",
+          "start": 57,
+          "end": 59,
+          "loc": {
+            "start": {
+              "line": 3,
+              "column": 16
+            },
+            "end": {
+              "line": 3,
+              "column": 18
+            }
+          },
+          "callProperties": [],
+          "properties": [],
+          "indexers": []
+        }
+      }
+    ],
+    "directives": []
+  }
+}
\ No newline at end of file