feat(compiler): Implement constant string concat propagation

Resolves #29617

Author: nikeee

compiler/crates/react_optimization/src/constant_propagation.rs

@@ -232,7 +232,7 @@ fn apply_binary_operator(
             BinaryOperator::StrictEquals => Some(JsValue::Boolean(left.strictly_equals(right))),
             BinaryOperator::NotStrictEquals => {
                 Some(JsValue::Boolean(left.not_strictly_equals(right)))
-            }
+            },
             _ => None,
         },
     }

compiler/packages/babel-plugin-react-compiler/src/Optimization/ConstantPropagation.ts

@@ -327,6 +327,8 @@ function evaluateInstruction(
           case "+": {
             if (typeof lhs === "number" && typeof rhs === "number") {
               result = { kind: "Primitive", value: lhs + rhs, loc: value.loc };
+            } else if (typeof lhs === "string" && typeof rhs === "string") {
+              result = { kind: "Primitive", value: lhs + rhs, loc: value.loc };
             }
             break;
           }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/constant-propagation-string-concat.expect.md

@@ -0,0 +1,35 @@
+
+## Input
+
+```javascript
+function foo() {
+  const a = "a" + "b";
+  const c = "c";
+  return a + c;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: foo,
+  params: [],
+  isComponent: false,
+};
+
+```
+
+## Code
+
+```javascript
+function foo() {
+  return "abc";
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: foo,
+  params: [],
+  isComponent: false,
+};
+
+```
+      
+### Eval output
+(kind: ok) "abc"

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/constant-propagation-string-concat.js

@@ -0,0 +1,11 @@
+function foo() {
+  const a = "a" + "b";
+  const c = "c";
+  return a + c;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: foo,
+  params: [],
+  isComponent: false,
+};