From 5ee23af1a6d10b79e96c6bf82a28e1bef5b0130a Mon Sep 17 00:00:00 2001
From: Joe Savona <joesavona@fb.com>
Date: Wed, 17 May 2023 15:55:51 -0700
Subject: [PATCH] Elide empty if alternate blocks in codegen

---
 .../ReactiveScopes/CodegenReactiveFunction.ts | 17 ++++----
 .../constant-propagation-phi.expect.md        |  1 -
 .../compiler/reverse-postorder.expect.md      |  1 -
 .../rules-of-hooks-c1e8c7f4c191.expect.md     | 40 -------------------
 4 files changed, 10 insertions(+), 49 deletions(-)

diff --git a/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts b/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts
index 11a189d18f..473dbb8906 100644
--- a/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts
+++ b/compiler/forget/src/ReactiveScopes/CodegenReactiveFunction.ts
@@ -385,13 +385,16 @@ function codegenTerminal(
       );
     }
     case "if": {
-      return t.ifStatement(
-        codegenPlace(cx, terminal.test),
-        codegenBlock(cx, terminal.consequent),
-        terminal.alternate !== null
-          ? codegenBlock(cx, terminal.alternate)
-          : null
-      );
+      const test = codegenPlace(cx, terminal.test);
+      const consequent = codegenBlock(cx, terminal.consequent);
+      let alternate: t.Statement | null = null;
+      if (terminal.alternate !== null) {
+        const block = codegenBlock(cx, terminal.alternate);
+        if (block.body.length !== 0) {
+          alternate = block;
+        }
+      }
+      return t.ifStatement(test, consequent, alternate);
     }
     case "return": {
       const value = codegenPlace(cx, terminal.value);
diff --git a/compiler/forget/src/__tests__/fixtures/compiler/constant-propagation-phi.expect.md b/compiler/forget/src/__tests__/fixtures/compiler/constant-propagation-phi.expect.md
index a0a4f00831..0ad43506d1 100644
--- a/compiler/forget/src/__tests__/fixtures/compiler/constant-propagation-phi.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/compiler/constant-propagation-phi.expect.md
@@ -23,7 +23,6 @@ function foo(a, b, c) {
 ```javascript
 function foo(a, b, c) {
   if (a) {
-  } else {
   }
   return b;
 }
diff --git a/compiler/forget/src/__tests__/fixtures/compiler/reverse-postorder.expect.md b/compiler/forget/src/__tests__/fixtures/compiler/reverse-postorder.expect.md
index 1153d8dea3..50708f6147 100644
--- a/compiler/forget/src/__tests__/fixtures/compiler/reverse-postorder.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/compiler/reverse-postorder.expect.md
@@ -51,7 +51,6 @@ function Component(props) {
     }
   } else {
     if (props.cond2) {
-    } else {
     }
   }
 }
diff --git a/compiler/forget/src/__tests__/fixtures/compiler/rules-of-hooks/rules-of-hooks-c1e8c7f4c191.expect.md b/compiler/forget/src/__tests__/fixtures/compiler/rules-of-hooks/rules-of-hooks-c1e8c7f4c191.expect.md
index fd04af4171..7761022d62 100644
--- a/compiler/forget/src/__tests__/fixtures/compiler/rules-of-hooks/rules-of-hooks-c1e8c7f4c191.expect.md
+++ b/compiler/forget/src/__tests__/fixtures/compiler/rules-of-hooks/rules-of-hooks-c1e8c7f4c191.expect.md
@@ -147,124 +147,84 @@ function MyComponent() {
 // Is valid but hard to compute by brute-forcing
 function MyComponent() {
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
   if (c) {
-  } else {
   }
 
   useHook();