fix stack overflow in render_document

[Yoorkin]

fix #8

[peter-jerry-ye-code-review]

‼️ This code review is generated by a bot. Please verify the content before trusting it.

Based on the diff, this pull request introduces changes to address Issue #8, which seems to be related to stack safety in the render_document function. The main change is converting the recursive aux function into an iterative approach using a queue. Additionally, a new test file test.mbt is added to verify the stack safety.

Here's the review of the changes:

💡 [Issue #8: Stack Safety Improvement]

• Category: Performance
• Code Snippet: src/document.mbt line 93-121
• Recommendation: The change from recursion to iteration using a queue is the correct approach to prevent stack overflow.
• Reasoning: The original implementation was recursive, which could lead to stack overflow with deeply nested documents. Using a queue-based iterative approach ensures that the function remains stack-safe, especially for large documents. The new test in test.mbt verifies this by creating a large document with 3000 elements.

⚠️ [StringBuilder Usage]

• Category: Correctness
• Code Snippet: let buf = StringBuilder::new()
• Recommendation: Clarify or verify the exact implementation of StringBuilder since it was previously @buffer.new().
• Reasoning: There's a change from @buffer.new() to StringBuilder::new(). This needs to be verified for correctness since it's unclear whether StringBuilder is a standard library component or a custom implementation. Ensure that StringBuilder has the same or compatible methods as the previous buffer implementation.

💡 [Test Coverage for Stack Safety]

• Category: Maintainability
• Code Snippet: src/test.mbt lines 1-8
• Recommendation: The added test case is good but could be expanded to check the correctness of the rendered output.
• Reasoning: The test verifies that the render_document function can handle a large document without stack overflow, but it does not assert the correctness of the output. Adding assertions on the rendered string would make the test more comprehensive.

Overall, the changes effectively address the stack safety issue, but minor improvements to documentation, testing, and clarity around StringBuilder would further enhance the code quality.

[illusory0x0]

use @deque.T represent Concat.

diff --git a/src/types.mbt b/src/types.mbt
index 98fefe2..a6e92e1 100644
--- a/src/types.mbt
+++ b/src/types.mbt
@@ -9,7 +9,7 @@ enum Document {
   Empty
   Line
   Text(String)
-  Concat(Requirement, Document, Document)
+  Concat(Requirement, @deque.T[Document])
   Group(Requirement, Document)
   Switch(Requirement, Document, Document)
   Nest(Requirement, Int, Document)