Splitting .zng Headers: A Guide To Efficient Code Generation

by Luna Greco 61 views

Discussion

Hey guys,

With the merging of #43, there's a growing possibility of generating massive generated.h files. To tackle this, we need a system that supports splitting generated.h into multiple headers. Let's dive into the details and explore how we can make this happen.

The Challenge of Massive generated.h Files

As our projects grow, the generated.h file can become unwieldy, making compilation slower and the codebase harder to manage. We need a solution that allows us to break down this large file into smaller, more manageable chunks. One approach is to create a separate header for each crate that contributes symbols to the ZngurSpec. This method, while conceptually simple, faces some practical hurdles.

The Complexity of Symbol Re-opening

One of the main challenges is that symbols, especially those from the standard library (std), can be "re-opened" in different .zng files. We want each .zng file that re-opens a symbol to have its Foreign Function Interface (FFI) code in the crate's generated header. This means we need a way to track which .zng files mention which symbols.

Tracking Symbols and Creating Headers

To achieve this, we need to track which .zng files mention specific symbols. Once we have this information, we can create a header for each set of headers that mention common symbols. This internal, "shared" header will then be included by each individual header, creating the desired effect. Let's look at an example to illustrate this.

Example Scenario

Consider the following .zng files:

a.zng

mod ::std {
    type option::Option<i32> {
        #layout(size = 8, align = 4);

        constructor None;
        constructor Some(i32);
    }
}

type Box<dyn Fn(i32) -> i32> {
    #layout(size = 8, align = 4);
}

In this file, we define an Option type with constructors None and Some, and a Box type for a function that takes and returns i32.

b.zng

mod ::std {
    type option::Option<i32> {
        #layout(size = 8, align = 4);
        fn unwrap(self) -> i32;
    }

    mod vec {
        type Vec {...}
    }
}

Here, we extend the Option type with an unwrap function and define a Vec type.

Generated Headers

Based on these .zng files, we would generate the following headers:

internal/generated/ab.h (Not Exposed to Users)

// internal/generated/ab.h
// Insert `option::Option FFI` here

This internal header includes the FFI for option::Option, which is shared between a.zng and b.zng.

generated/a.h (Exposed to Users)

// generated/a.h
#include <internal/generated/ab.h>
// Insert `Box<dyn Fn(i32) -> i32>` FFI here

This header includes the shared header and adds the FFI for Box<dyn Fn(i32) -> i32>. It's the header that users of a.zng would include.

generated/b.h (Exposed to Users)

// generated/b.h
#include <internal/generated/ab.h>
// Insert `Vec` FFI here

Similarly, this header includes the shared header and adds the FFI for Vec. Users of b.zng would include this header.

Benefits of Separate Headers

By splitting the generated code into separate headers, we achieve several benefits:

  1. Reduced Compilation Time: Smaller headers mean less code to parse and compile, which can significantly reduce compilation times.
  2. Improved Code Organization: Breaking down the generated code into logical units makes the codebase easier to navigate and understand.
  3. Reduced Dependencies: Changes in one .zng file are less likely to trigger recompilation in other parts of the project.
  4. Easier Maintenance: Smaller files are easier to maintain and debug.

Implementation Strategy

To implement this, we need to:

  1. Track Symbol Usage: Keep track of which .zng files mention each symbol.
  2. Identify Shared Symbols: Determine which symbols are shared across multiple .zng files.
  3. Generate Internal Headers: Create internal headers for shared symbols.
  4. Generate Public Headers: Create public headers for each .zng file, including the necessary internal headers.

This approach ensures that we generate efficient and maintainable code while addressing the issue of massive generated.h files. Let's explore these steps in more detail.

Detailed Implementation Steps

Let’s break down the implementation into more manageable steps:

  1. Symbol Tracking Mechanism:

    • Keyword: Symbol Tracking
    • We need a robust system to track where each symbol is used. A straightforward approach is to use a hash map where keys are symbol names, and values are sets of .zng file paths. This allows us to quickly look up all the files that mention a particular symbol.
    • When the Zngur compiler processes a .zng file, it updates this hash map. For every symbol encountered, the compiler adds the file path to the set associated with that symbol. This ensures we have a comprehensive record of symbol usage across all files.
    • For example, if a.zng and b.zng both mention Option, the hash map would store Option as a key, with a value set containing paths to both a.zng and b.zng. This information is crucial for the next steps.

  2. Identifying Shared Symbols:

    • Keyword: Shared Symbol Identification
    • Once we have the symbol usage data, we need to identify which symbols are shared among multiple .zng files. We can iterate through the symbol usage hash map and identify symbols associated with more than one file path. These symbols are considered shared and will be placed in internal headers.
    • For our example, Option would be identified as a shared symbol because it is used in both a.zng and b.zng. Symbols like Box (used only in a.zng) and Vec (used only in b.zng) would not be considered shared.
    • Identifying shared symbols is a critical step in minimizing code duplication and ensuring that common FFI code is grouped logically.

  3. Generating Internal Headers:

    • Keyword: Internal Header Generation
    • For each set of shared symbols, we generate an internal header file. These headers are not intended for direct inclusion by users but serve as a repository for common FFI code. The naming convention for these headers could follow a pattern like internal/generated/ab.h, where ab represents that the header is shared between a.zng and b.zng.
    • The content of these headers includes the FFI declarations and definitions for the shared symbols. In our example, internal/generated/ab.h would contain the FFI code for Option. This approach ensures that the FFI code for shared symbols is centralized, reducing redundancy and making maintenance easier.

  4. Generating Public Headers:

    • Keyword: Public Header Generation
    • For each .zng file, we generate a public header file that users will include in their C++ code. These headers include the necessary internal headers and contain the FFI code for symbols unique to the .zng file.
    • For a.zng, the generated header generated/a.h would include internal/generated/ab.h and contain the FFI code for Box. Similarly, generated/b.h would include internal/generated/ab.h and contain the FFI code for Vec.
    • This structure ensures that each public header only contains the code relevant to its corresponding .zng file, plus the shared code from internal headers. This modularity reduces compile times and improves code organization.

Benefits Revisited

Revisiting the benefits, this implementation strategy effectively addresses the initial concerns and provides significant advantages:

  • Reduced Compilation Time: By splitting the generated code into smaller, logical units, we minimize the amount of code that needs to be parsed and compiled for each file.
  • Improved Code Organization: The separation of shared and unique symbols into internal and public headers enhances the structure and maintainability of the generated code.
  • Reduced Dependencies: Changes to a shared symbol’s FFI only require recompilation of the files that include the corresponding internal header, rather than the entire project.
  • Easier Maintenance: Smaller, focused headers are easier to understand, debug, and maintain.

Conclusion

Implementing separate headers for imported .zng files is crucial for managing large projects and ensuring efficient compilation. By tracking symbol usage, identifying shared symbols, and generating internal and public headers, we can create a more modular and maintainable codebase. This approach not only solves the immediate problem of massive generated.h files but also lays the foundation for future scalability and maintainability. This detailed strategy ensures that the Zngur compiler can handle projects of any size with ease.

Additional Information

HKalbasi, zngur