[hir] Store env in HIRFunction

The env is specific to the HIR function anwyays. It's not very useful outside 
the HIRFunction.

compiler/forget/src/CompilerPipeline.ts

@@ -42,9 +42,7 @@ export type CompilerPipelineValue =
 export function* run(
   func: NodePath<t.FunctionDeclaration>
 ): Generator<CompilerPipelineValue, t.Function> {
-  const env = new Environment();
-
-  const lowering = lower(func, env).orElse((errors) => {
+  const lowering = lower(func).orElse((errors) => {
     const msg = errors.map((error) => error.toString()).join("\n\n");
     throw new Error(msg);
   });
@@ -55,7 +53,7 @@ export function* run(
   mergeConsecutiveBlocks(hir);
   yield log({ kind: "hir", name: "MergeConsecutiveBlocks", value: hir });
 
-  enterSSA(hir, env);
+  enterSSA(hir);
   yield log({ kind: "hir", name: "SSA", value: hir });
 
   eliminateRedundantPhi(hir);

compiler/forget/src/HIR/BuildHIR.ts

@@ -48,9 +48,9 @@ import HIRBuilder, { Environment } from "./HIRBuilder";
  * grained reactivity.
  */
 export function lower(
-  func: NodePath<t.Function>,
-  env: Environment
+  func: NodePath<t.Function>
 ): Result<HIRFunction, CompilerError[]> {
+  const env = new Environment();
   const builder = new HIRBuilder(env);
 
   const id =
@@ -106,6 +106,7 @@ export function lower(
     generator: func.node.generator === true,
     async: func.node.async === true,
     loc: func.node.loc ?? GeneratedSource,
+    env,
   });
 }
 

compiler/forget/src/HIR/HIR.ts

@@ -7,6 +7,7 @@
 
 import * as t from "@babel/types";
 import invariant from "invariant";
+import { Environment } from "./HIRBuilder";
 
 // *******************************************************************************************
 // *******************************************************************************************
@@ -161,6 +162,7 @@ export type ReactiveIfTerminal = {
 export type HIRFunction = {
   loc: SourceLocation;
   id: Identifier | null;
+  env: Environment;
   params: Array<Place>;
   body: HIR;
   generator: boolean;

compiler/forget/src/SSA/EnterSSA.ts

@@ -182,9 +182,9 @@ class SSABuilder {
   }
 }
 
-export default function enterSSA(func: HIRFunction, env: Environment) {
+export default function enterSSA(func: HIRFunction) {
   const visitedBlocks: Set<BasicBlock> = new Set();
-  const builder = new SSABuilder(env, func.body.blocks);
+  const builder = new SSABuilder(func.env, func.body.blocks);
   for (const [blockId, block] of func.body.blocks) {
     invariant(
       !visitedBlocks.has(block),