Initial implementation of basic F# pipeline

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

@@ -321,8 +321,16 @@ export default class ExpressionParser extends LValParser {
 
         if (op === tt.pipeline) {
           this.expectPlugin("pipelineOperator");
+          const wasInPipeline = this.state.inPipeline;
           this.state.inPipeline = true;
           this.checkPipelineAtInfixOperator(left, leftStartPos);
+
+          if (
+            this.getPluginOption("pipelineOperator", "proposal") === "fsharp" &&
+            !wasInPipeline
+          ) {
+            node.left = this.makePipelineHead(left);
+          }
         } else if (op === tt.nullishCoalescing) {
           this.expectPlugin("nullishCoalescingOperator");
         }
@@ -376,18 +384,21 @@ export default class ExpressionParser extends LValParser {
     prec: number,
     noIn: ?boolean,
   ): N.Expression {
+    const startPos = this.state.start;
+    const startLoc = this.state.startLoc;
     switch (op) {
       case tt.pipeline:
-        if (this.getPluginOption("pipelineOperator", "proposal") === "smart") {
-          const startPos = this.state.start;
-          const startLoc = this.state.startLoc;
-          return this.withTopicPermittingContext(() => {
-            return this.parseSmartPipelineBody(
-              this.parseExprOpBaseRightExpr(op, prec, noIn),
-              startPos,
-              startLoc,
-            );
-          });
+        switch (this.getPluginOption("pipelineOperator", "proposal")) {
+          case "smart":
+            return this.withTopicPermittingContext(() => {
+              return this.parseSmartPipelineBody(
+                this.parseExprOpBaseRightExpr(op, prec, noIn),
+                startPos,
+                startLoc,
+              );
+            });
+          case "fsharp":
+            return this.parseFSharpPipelineBody(op, prec, noIn);
         }
       // falls through
 
@@ -2271,4 +2282,31 @@ export default class ExpressionParser extends LValParser {
       this.state.topicContext.maxTopicIndex >= 0
     );
   }
+
+  makePipelineHead(left: N.Expression): N.Expression {
+    const node = this.startNode();
+    node.head = left;
+
+    return this.finishNode(node, "PipelineHead");
+  }
+
+  parseFSharpPipelineBody(
+    op: TokenType,
+    prec: number,
+    noIn: ?boolean,
+  ): N.Expression {
+    const startPos = this.state.start;
+    const startLoc = this.state.startLoc;
+
+    const node = this.startNodeAt(this.state.start, this.state.startLoc);
+    node.body = this.parseExprOp(
+      this.parseMaybeUnary(),
+      startPos,
+      startLoc,
+      op.rightAssociative ? prec - 1 : prec,
+      noIn,
+    );
+
+    return this.finishNode(node, "PipelineBody");
+  }
 }

packages/babel-parser/src/types.js

@@ -568,6 +568,10 @@ export type SequenceExpression = NodeBase & {
 
 // Pipelines
 
+export type PipelineHead = NodeBase & {
+  type: "PipelineHead",
+};
+
 export type PipelineBody = NodeBase & {
   type: "PipelineBody",
 };

packages/babel-parser/test/fixtures/experimental/pipeline-operator/invalid-proposal/options.json

@@ -1,6 +1,4 @@
 {
-  "plugins": [
-    ["pipelineOperator", { "proposal": "invalid" }]
-  ],
+  "plugins": [["pipelineOperator", { "proposal": "invalid" }]],
   "throws": "'pipelineOperator' requires 'proposal' option whose value should be one of: 'minimal', 'smart', 'fsharp'"
 }

packages/babel-parser/test/fixtures/experimental/pipeline-operator/proposal-fsharp-arrow-at-head-indented/input.js

@@ -0,0 +1 @@
+x => x |> inc |> double

packages/babel-parser/test/fixtures/experimental/pipeline-operator/proposal-fsharp-arrow-at-head-indented/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": [["pipelineOperator", { "proposal": "fsharp" }]]
+}

packages/babel-parser/test/fixtures/experimental/pipeline-operator/proposal-fsharp-arrow-at-head-indented/output.json

@@ -0,0 +1,215 @@
+{
+  "type": "File",
+  "start": 0,
+  "end": 23,
+  "loc": {
+    "start": {
+      "line": 1,
+      "column": 0
+    },
+    "end": {
+      "line": 1,
+      "column": 23
+    }
+  },
+  "program": {
+    "type": "Program",
+    "start": 0,
+    "end": 23,
+    "loc": {
+      "start": {
+        "line": 1,
+        "column": 0
+      },
+      "end": {
+        "line": 1,
+        "column": 23
+      }
+    },
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "ExpressionStatement",
+        "start": 0,
+        "end": 23,
+        "loc": {
+          "start": {
+            "line": 1,
+            "column": 0
+          },
+          "end": {
+            "line": 1,
+            "column": 23
+          }
+        },
+        "expression": {
+          "type": "ArrowFunctionExpression",
+          "start": 0,
+          "end": 23,
+          "loc": {
+            "start": {
+              "line": 1,
+              "column": 0
+            },
+            "end": {
+              "line": 1,
+              "column": 23
+            }
+          },
+          "id": null,
+          "generator": false,
+          "async": false,
+          "params": [
+            {
+              "type": "Identifier",
+              "start": 0,
+              "end": 1,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 0
+                },
+                "end": {
+                  "line": 1,
+                  "column": 1
+                },
+                "identifierName": "x"
+              },
+              "name": "x"
+            }
+          ],
+          "body": {
+            "type": "BinaryExpression",
+            "start": 5,
+            "end": 23,
+            "loc": {
+              "start": {
+                "line": 1,
+                "column": 5
+              },
+              "end": {
+                "line": 1,
+                "column": 23
+              }
+            },
+            "left": {
+              "type": "BinaryExpression",
+              "start": 5,
+              "end": 13,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 5
+                },
+                "end": {
+                  "line": 1,
+                  "column": 13
+                }
+              },
+              "left": {
+                "type": "PipelineHead",
+                "start": 7,
+                "end": 6,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 7
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 6
+                  }
+                },
+                "head": {
+                  "type": "Identifier",
+                  "start": 5,
+                  "end": 6,
+                  "loc": {
+                    "start": {
+                      "line": 1,
+                      "column": 5
+                    },
+                    "end": {
+                      "line": 1,
+                      "column": 6
+                    },
+                    "identifierName": "x"
+                  },
+                  "name": "x"
+                }
+              },
+              "operator": "|>",
+              "right": {
+                "type": "PipelineBody",
+                "start": 10,
+                "end": 13,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 10
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 13
+                  }
+                },
+                "body": {
+                  "type": "Identifier",
+                  "start": 10,
+                  "end": 13,
+                  "loc": {
+                    "start": {
+                      "line": 1,
+                      "column": 10
+                    },
+                    "end": {
+                      "line": 1,
+                      "column": 13
+                    },
+                    "identifierName": "inc"
+                  },
+                  "name": "inc"
+                }
+              }
+            },
+            "operator": "|>",
+            "right": {
+              "type": "PipelineBody",
+              "start": 17,
+              "end": 23,
+              "loc": {
+                "start": {
+                  "line": 1,
+                  "column": 17
+                },
+                "end": {
+                  "line": 1,
+                  "column": 23
+                }
+              },
+              "body": {
+                "type": "Identifier",
+                "start": 17,
+                "end": 23,
+                "loc": {
+                  "start": {
+                    "line": 1,
+                    "column": 17
+                  },
+                  "end": {
+                    "line": 1,
+                    "column": 23
+                  },
+                  "identifierName": "double"
+                },
+                "name": "double"
+              }
+            }
+          }
+        }
+      }
+    ],
+    "directives": []
+  }
+}

packages/babel-parser/test/fixtures/experimental/pipeline-operator/proposal-fsharp-arrow-at-head/input.js

@@ -0,0 +1 @@
+x => x |> inc |> double

packages/babel-parser/test/fixtures/experimental/pipeline-operator/proposal-fsharp-arrow-at-head/options.json

@@ -0,0 +1,3 @@
+{
+  "plugins": [["pipelineOperator", { "proposal": "fsharp" }]]
+}