fix(minifier): avoid merging if to for when the body contains a function declaration (#25637)

fixes https://github.com/oxc-project/oxc/issues/22222

I used AI to generate the code and then reviewed the code and changed the code and added tests.

crates/oxc_minifier/src/peephole/minimize_for_statement.rs

@@ -22,6 +22,23 @@ impl<'a> PeepholeOptimizations {
         let Statement::IfStatement(if_stmt) = first else {
             return;
         };
+
+        // Moving the condition into the `for` test changes its scope from the
+        // loop body's block scope to the surrounding scope. Block function
+        // declarations are initialized on entry, so the condition can observe
+        // them before their declaration statement. Other lexical declarations
+        // only differ through TDZ behavior, which the minifier intentionally
+        // ignores.
+        let body_has_function_declaration = match &for_stmt.body {
+            Statement::BlockStatement(block_stmt) => {
+                block_stmt.body.iter().skip(1).any(Self::statement_has_function_declaration)
+            }
+            _ => false,
+        };
+        if body_has_function_declaration {
+            return;
+        }
+
         // "for (;;) if (x) break;" => "for (; !x;) ;"
         // "for (; a;) if (x) break;" => "for (; a && !x;) ;"
         // "for (;;) if (x) break; else y();" => "for (; !x;) y();"
@@ -100,6 +117,16 @@ impl<'a> PeepholeOptimizations {
         }
     }
 
+    fn statement_has_function_declaration(stmt: &Statement<'a>) -> bool {
+        match stmt {
+            Statement::FunctionDeclaration(_) => true,
+            Statement::LabeledStatement(label) => {
+                Self::statement_has_function_declaration(&label.body)
+            }
+            _ => false,
+        }
+    }
+
     fn drop_first_statement(
         span: Span,
         body: Option<Statement<'a>>,

crates/oxc_minifier/tests/peephole/minimize_statements.rs

@@ -24,6 +24,33 @@ fn test_for_variable_declaration() {
     );
 }
 
+// https://github.com/oxc-project/oxc/issues/22222
+#[test]
+fn test_for_break_preserves_block_function_scope_in_module() {
+    test(
+        "let n = 0;
+        for (; n < 2; n++) {
+            if (typeof f === 'function') break;
+            function f() {}
+        }
+        console.log(n);",
+        "let n = 0;
+        for (; n < 2; n++) {
+            if (typeof f == 'function') break;
+            function f() {}
+        }
+        console.log(n);",
+    );
+    test(
+        "for (;;) { if (x) break; var y = foo(); bar(y); bar(y); }",
+        "for (; !x;) { var y = foo(); bar(y), bar(y); }",
+    );
+    test(
+        "for (;;) { if (x) break; let y = foo(); bar(y); bar(y); }",
+        "for (; !x;) { let y = foo(); bar(y), bar(y); }",
+    );
+}
+
 #[test]
 fn test_for_continue_in_for() {
     test("for( a of b ){ if(c) { continue; } d() }", "for ( a of b ) c || d();");