IntelliJ 2025.1: ~S Heredoc Injection Bug & Fixes

Hey guys! Let's dive into a quirky issue that's been popping up in IntelliJ 2025.1 and later versions. It's all about how SmartPsiElementPointers are behaving inside injected elements within ~S heredocs. Sounds like a mouthful, right? Don't worry, we'll break it down! This issue has some serious implications for code navigation and search functionalities, so it’s crucial we get to the bottom of it.

Understanding the Glitch: SmartPsiElementPointer Restoration Woes

The core of the problem lies in how IntelliJ handles SmartPsiElementPointers within a specific type of heredoc – the non-interpolating sigil (~S"""). Now, if language injection happens inside these heredocs, things get a bit tricky. A SmartPsiElementPointer is essentially a smart bookmark that IntelliJ uses to keep track of code elements. But in this scenario, these bookmarks are failing to restore properly, leading to some frustrating issues. To truly grasp the problem, let's unpack the key components and the sequence of events that trigger this bug.

The Key Players in This Drama

• Heredocs: Think of heredocs as multi-line strings in Elixir. They allow you to define strings that span multiple lines without needing to escape special characters. This is super handy for embedding larger chunks of text or code snippets within your code.
• Non-Interpolating Sigils (~S"""): These are special types of heredocs where variable interpolation is disabled. This means the content inside the heredoc is treated literally, without any variable substitution. It's like saying, "Hey, IntelliJ, take this exactly as it is!"
• Language Injection: This is a neat IntelliJ feature where the IDE recognizes that a certain part of your code should be treated as a different language (like HTML or SQL) and provides the appropriate code assistance (syntax highlighting, code completion, etc.).
• SmartPsiElementPointers: As mentioned earlier, these are smart bookmarks that IntelliJ uses to keep track of code elements. They're more robust than simple pointers because they can still locate the element even if the code around it changes.

The Sequence of Unfortunate Events

The issue seems to occur when the following conditions are met:

1. You're using a non-interpolating sigil (~S""") heredoc.
2. Language injection is happening inside this heredoc. Imagine you're embedding a snippet of SQL code within your Elixir code using a ~S heredoc.
3. A SmartPsiElementPointer is created for an element within the injected code. For example, the IDE might create a pointer to a specific SQL table name.

So, what goes wrong? Well, it appears that IntelliJ 2025.1+ has become stricter about how these pointers are restored. The IDE now throws an error if the pointer can't be accurately mapped back to its original location within the host code. This mapping process involves something called a LiteralTextEscaper, which is responsible for translating offsets between the injected code and the host code. And that's where the hiccup occurs!

The LiteralTextEscaper Breakdown

The LiteralTextEscaper is a crucial component in this process. It acts as a translator, converting positions (offsets) within the injected code back to their corresponding positions within the original Elixir code (the host). This is necessary because the injected code might have different formatting or escaping rules compared to the host code. For example, indentation might be stripped from the injected code, or special characters might be unescaped.

However, it seems that the current implementation of the LiteralTextEscaper for ElixirLiteralSigilHeredocImpl is failing in certain cases. Specifically, the decode method, which is responsible for converting offsets from the injected code to the host code, isn't working correctly. This is likely due to the way indentation is trimmed and the terminator is removed during the decoding process, causing offsets to shift and the mapping to fail.

Why Did This Fly Under the Radar Before?

That's a great question! It turns out that earlier versions of IntelliJ were more forgiving in this scenario. Instead of throwing an error when the pointer restoration failed, they simply logged it as a warning. This meant that the issue was lurking in the background, but it didn't cause any immediate problems. Now that IntelliJ is throwing an error, the problem has become much more visible and disruptive.

Impact: Brace Yourselves for Broken Features

So, what's the big deal? Why should you care about this obscure bug? Well, the impact is actually quite significant. Any feature that relies on SmartPsiElementPointers for injected elements within ~S heredocs is going to break in IntelliJ 2025.1+. This includes:

• Find Usages: The "Find Usages" feature allows you to quickly locate all the places where a particular code element (like a function or variable) is used. If SmartPsiElementPointers are failing, this feature won't work correctly for injected elements.
• Search Features: Similar to "Find Usages," other search-related features will also be affected. This can make it much harder to navigate your codebase and understand how different parts of your code are connected.
• Refactoring: Refactoring tools often rely on SmartPsiElementPointers to safely update code elements across your project. If these pointers are broken, refactoring operations might not work correctly, potentially leading to code corruption.

Specifically, the bug affects tests like FindUsagesTest.testFunctionRecursiveUsage and other tests that scan core Elixir files like kernel.ex. This means that even core Elixir functionality might be impacted, which is a serious concern.

Possible Fixes: Let's Get Technical

Okay, so we've identified the problem and its impact. Now, let's talk about potential solutions. There are a couple of approaches we can take to address this issue.

1. Identity Escaper for ~S Heredocs: The 1:1 Mapping Approach

This fix proposes a more direct and straightforward mapping for non-interpolating heredocs. The idea is to treat the decoded text as a mirror image of the host range, without any trimming or unescaping. This means that the getOffsetInHost calculation becomes a simple addition, making the mapping process much more reliable.

Essentially, we're saying, "For ~S heredocs, let's just assume that the offsets in the injected code are the same as the offsets in the host code." This avoids the complexities of the current LiteralTextEscaper implementation, which is where the bug seems to be originating.

• Pros:
  • Simpler and more direct mapping.
  • Avoids the offset shifting issues caused by trimming and unescaping.
  • Potentially more performant.
• Cons:
  • Might not be suitable for all types of heredocs (only non-interpolating ones).
  • Requires careful consideration of edge cases.

2. Skip Injection in ~S Heredocs Entirely: The Temporary Workaround

This fix suggests a more drastic but potentially quicker solution: simply disable language injection within ~S heredocs altogether. This would effectively sidestep the issue by preventing SmartPsiElementPointers from being created in the first place.

Think of it as putting a temporary bandage on the problem. It doesn't fix the underlying issue, but it prevents it from causing immediate harm.

• Pros:
  • Relatively easy to implement.
  • Provides an immediate workaround for the bug.
• Cons:
  • Sacrifices language injection features (syntax highlighting, code completion, etc.) within ~S heredocs.
  • Only a temporary solution; the underlying issue still needs to be addressed.

Conclusion: A Call to Action

So, there you have it! The SmartPsiElementPointer restoration failure in IntelliJ 2025.1+ is a tricky bug with some serious implications. It affects core code navigation and search features, and it's crucial that we address it promptly. Whether it's the 1:1 mapping approach or temporarily skipping injection, a solution is needed to ensure a smooth coding experience for developers.

Keep an eye on this issue, and let's hope for a fix soon! Happy coding, guys!