Add babel transform to deconstruct Wonka's pipe (#419)

* Add babel transform to deconstruct Wonka's pipe

* Add tracking for actual import alias

* Fix pipeExpression order

This imitates Wonka's pipe algo so that it's easier
to follow. Also the previous one was incorrect

rollup.config.js

@@ -6,6 +6,7 @@ import buble from 'rollup-plugin-buble';
 import babel from 'rollup-plugin-babel';
 import replace from 'rollup-plugin-replace';
 import { terser } from 'rollup-plugin-terser';
+import transformPipe from './scripts/transform-pipe';
 
 const pkgInfo = require('./package.json');
 const external = ['dns', 'fs', 'path', 'url'];
@@ -119,8 +120,9 @@ const makePlugins = (isProduction = false) => [
     exclude: 'node_modules/**',
     presets: [],
     plugins: [
-      ['babel-plugin-closure-elimination', {}],
-      ['@babel/plugin-transform-object-assign', {}],
+      transformPipe,
+      'babel-plugin-closure-elimination',
+      '@babel/plugin-transform-object-assign',
       ['@babel/plugin-transform-react-jsx', {
         pragma: 'React.createElement',
         pragmaFrag: 'React.Fragment',

scripts/transform-pipe.js

@@ -0,0 +1,44 @@
+const pipeExpression = (t, pipeline) => {
+  let x = pipeline[0];
+  for (let i = 1; i < pipeline.length; i++)
+    x = t.callExpression(pipeline[i], [x]);
+  return x;
+};
+
+const pipePlugin = ({ types: t }) => ({
+  visitor: {
+    ImportDeclaration(path, state) {
+      if (path.node.source.value === 'wonka') {
+        const { specifiers } = path.node;
+        const pipeSpecifierIndex = specifiers.findIndex(spec => {
+          return spec.imported.name === 'pipe';
+        });
+
+        if (pipeSpecifierIndex > -1) {
+          const pipeSpecifier = specifiers[pipeSpecifierIndex];
+          state.pipeName = pipeSpecifier.local.name;
+          if (specifiers.length > 1) {
+          path.node.specifiers.splice(pipeSpecifierIndex, 1);
+          } else {
+          	path.remove();
+          }
+        }
+      }
+    },
+    CallExpression(path, state) {
+      if (state.pipeName) {
+        const callee = path.node.callee;
+        const args = path.node.arguments;
+        if (callee.name !== state.pipeName) {
+          return;
+        } else if (args.length === 0) {
+          path.replaceWith(t.identifier('undefined'));
+        } else {
+          path.replaceWith(pipeExpression(t, args));
+        }
+      }
+    }
+  }
+});
+
+export default pipePlugin;