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macro iftree

Include many files in your Rust code for self-contained binaries

7 releases (stable)

1.0.4 Feb 1, 2023
1.0.3 Feb 5, 2022
1.0.2 Aug 29, 2021
1.0.1 Jul 5, 2021
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#522 in Filesystem

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MIT license


Iftree: Include File Tree 🌳

Include many files in your Rust code for self-contained binaries.


  • Include or exclude files with path patterns.
  • File lookups checked at compile time are fast at runtime (constant time).
  • Customizable: associate any data with files.
  • Many examples, including recipes.

See also related projects.

Test crates.io


Self-contained binaries are easy to ship, as they come with any required file data such as game assets, web templates, etc.

The standard library's std::include_str! includes the contents of a given file. Iftree generalizes this in two ways:

  • Not just one, but many files can be included at once with path patterns in a .gitignore-like format. Patterns are flexible: you can include multiple folders, skip hidden files, filter by filename extension, select a fixed file list, etc.
  • Instead of including the file contents only, files can be associated with any data fields such as additional file metadata.


std:       include_str!("my_file")
Iftree:    any_macro!("my_files/**")


Now that you know the why and the what, learn the how. The following quick start shows the basic usage.

Quick start

// Say you have these files:
//     my_assets/
//     ├── file_a
//     ├── file_b
//     └── folder/
//         └── file_c

// Include data from this file tree in your code like so:
#[iftree::include_file_tree("paths = '/my_assets/**'")]
pub struct MyAsset {
    relative_path: &'static str,
    contents_str: &'static str,

fn main() {
    // Based on this, an array `ASSETS` of `MyAsset` instances is generated:
    assert_eq!(ASSETS.len(), 3);
    assert_eq!(ASSETS[0].relative_path, "my_assets/file_a");
    assert_eq!(ASSETS[0].contents_str, "… contents file_a\n");
    assert_eq!(ASSETS[1].contents_str, "… contents file_b\n");
    assert_eq!(ASSETS[2].contents_str, "… file_c\n");

    // Also, variables `base::x::y::MY_FILE` are generated (named by file path):
    assert_eq!(base::my_assets::FILE_A.relative_path, "my_assets/file_a");
    assert_eq!(base::my_assets::FILE_A.contents_str, "… contents file_a\n");
    assert_eq!(base::my_assets::FILE_B.contents_str, "… contents file_b\n");
    assert_eq!(base::my_assets::folder::FILE_C.contents_str, "… file_c\n");

Detailed guide

  1. Add the dependency iftree = "1.0" to your manifest (Cargo.toml).

  2. Define your asset type, which is just a custom struct or type alias. Example:

    pub struct MyAsset;
  3. Next, filter files to be included by annotating your asset type. Example:

    #[iftree::include_file_tree("paths = '/my_assets/**'")]
    pub struct MyAsset;

    The macro argument is a TOML string literal. Its paths option here supports .gitignore-like path patterns, with one pattern per line. These paths are relative to the folder with your manifest by default. See the paths configuration for more.

  4. Define the data fields of your asset type. Example:

    #[iftree::include_file_tree("paths = '/my_assets/**'")]
    pub struct MyAsset {
        relative_path: &'static str,
        contents_bytes: &'static [u8],

    When building your project, code is generated that instantiates the asset type once per file.

    By default, a field relative_path (if any) is populated with the file path, a field contents_bytes is populated with the raw file contents, and a couple of other standard fields are recognized by name.

    However, you can customize this to include arbitrary file data.

  5. Now you can access your file data via the generated ASSETS array. Example:

    assert_eq!(ASSETS[0].relative_path, "my_assets/my_file");
    assert_eq!(ASSETS[0].contents_bytes, b"file contents");

    Additionally, for each file x/y/my_file, a variable base::x::y::MY_FILE is generated (unless disabled via template.identifiers configuration). Such a variable is a reference to the respective element of the ASSETS array. Example:

    assert_eq!(base::my_assets::MY_FILE.relative_path, "my_assets/my_file");
    assert_eq!(base::my_assets::MY_FILE.contents_bytes, b"file contents");


If you like to explore by example, there is an examples folder. The documentation links to individual examples where helpful.

You could get started with the basic example. For a more complex case, see the showcase example.

Note that some examples need extra dependencies from the dev-dependencies of the manifest.

Standard fields

When you use a subset of the following fields only, an initializer for your asset type is generated without further configuration. See example.

  • contents_bytes: &'static [u8]

    File contents as a byte array, using std::include_bytes.

  • contents_str: &'static str

    File contents interpreted as a UTF-8 string, using std::include_str.

  • get_bytes: fn() -> std::borrow::Cow<'static, [u8]>

    In debug builds (that is, when debug_assertions is enabled), this function reads the file afresh on each call at runtime. It panics if there is any error such as if the file does not exist. This helps with faster development, as it avoids rebuilding if asset file contents are changed only (note that you still need to rebuild if assets are added, renamed, or removed).

    In release builds, it returns the file contents included at compile time, using std::include_bytes.

  • get_str: fn() -> std::borrow::Cow<'static, str>

    Same as get_bytes but for the file contents interpreted as a UTF-8 string, using std::include_str.

  • relative_path: &'static str

    File path relative to the base folder, which is the folder with your manifest (Cargo.toml) by default. Path components are separated by a slash /, independent of your platform.

Custom file data

To associate custom data with your files, you can plug in a macro that initializes each asset. Toy example:

macro_rules! my_initialize {
    ($relative_path:literal, $absolute_path:literal) => {
        MyAsset {
            path: $relative_path,
            size_in_bytes: include_bytes!($absolute_path).len(),

paths = '/my_assets/**'
template.initializer = 'my_initialize'
pub struct MyAsset {
    path: &'static str,
    size_in_bytes: usize,

fn main() {
    assert_eq!(base::my_assets::FILE_A.path, "my_assets/file_a");
    assert_eq!(base::my_assets::FILE_A.size_in_bytes, 20);
    assert_eq!(base::my_assets::FILE_B.path, "my_assets/file_b");

The initializer macro (my_initialize above) must return a constant expression. Non-constant data can still be computed (lazily) with a library like once_cell.

For even more control over code generation, there is the concept of visitors.

Name sanitization

When generating identifiers based on paths, names are sanitized. For example, a filename 404_not_found.md is sanitized to an identifier _404_NOT_FOUND_MD.

The sanitization process is designed to generate valid, conventional identifiers. Essentially, it replaces invalid identifier characters by underscores "_" and adjusts the letter case to the context.

More precisely, these transformations are applied in order:

  1. The case of letters is adjusted to respect naming conventions:
    • All lowercase for folders (because they map to module names).
    • All uppercase for filenames (because they map to static variables).
  2. Characters without the property XID_Continue are replaced by "_". The set of XID_Continue characters in ASCII is [0-9A-Z_a-z].
  3. If the first character does not belong to XID_Start and is not "_", then "_" is prepended. The set of XID_Start characters in ASCII is [A-Za-z].
  4. If the name is "_", "crate", "self", "Self", or "super", then "_" is appended.

Portable file paths

To prevent issues when developing on different platforms, your file paths should follow these recommendations:

  • Path components are separated by a slash / (even on Windows).
  • Filenames do not contain backslashes \ (even on Unix-like systems).


To inspect the generated code, there is a debug configuration.


Here are example solutions for given problems.

Kinds of asset types

Integration with other libraries

Including file metadata

Custom constructions

Originally, I've worked on Iftree because I couldn't find a library for this use case: including files from a folder filtered by filename extension. The project has since developed into something more flexible.

Here is how I think Iftree compares to related projects for the given criteria. Generally, while Iftree has defaults to address common use cases, it comes with first-class support for arbitrary file data.

Project File selection Included file data Data access via
include_dir 0.7 Single folder Path, contents, metadata File path, nested iterators, glob patterns
includedir 0.6 Multiple files, multiple folders Path, contents File path, iterator
Rust Embed 6.4 Single folder, inclusion-exclusion path patterns Path, contents, metadata File path, iterator
std::include_bytes Single file Contents File path
std::include_str Single file Contents File path
Iftree Multiple files by inclusion-exclusion path patterns Path, contents, custom File path (via base::x::y::MY_FILE variables in constant time), iterator (ASSETS array), custom

Configuration reference

The iftree::include_file_tree macro is configured via a TOML string with the following fields.


Path patterns are interpreted as relative to this folder.

Unless this path is absolute, it is interpreted as relative to the folder given by the environment variable CARGO_MANIFEST_DIR. That is, a path pattern x/y/z resolves to [CARGO_MANIFEST_DIR]/[base_folder]/x/y/z.

See the root_folder_variable configuration to customize this.

Default: ""

See example.


Whether to generate a string variable DEBUG with debug information such as the generated code.

Default: false

See example.


A string with a path pattern per line to filter files.

It works like a .gitignore file with inverted meaning:

  • If the last matching pattern is negated (with !), the file is excluded.
  • If the last matching pattern is not negated, the file is included.
  • If no pattern matches, the file is excluded.

The pattern language is as documented in the .gitignore reference, with this difference: you must use x/y/* instead of x/y/ to include files in a folder x/y/; to also include subfolders (recursively), use x/y/**.

By default, path patterns are relative to the environment variable CARGO_MANIFEST_DIR, which is the folder with your manifest (Cargo.toml). See the base_folder configuration to customize this.

Common patterns:

  • Exclude hidden files: !.*
  • Include files with filename extension xyz only: *.xyz

This is a required option without default.

See example.


An environment variable that is used to resolve a relative base_folder to an absolute path.

The value of the environment variable should be an absolute path.



Whether to generate an identifier per file.

Given a file x/y/my_file, a static variable base::x::y::MY_FILE is generated, nested in modules for folders. Their root module is base, which represents the base folder.

Each variable is a reference to the corresponding element of the ASSETS array.

Generated identifiers are subject to name sanitization. Because of this, two files may map to the same identifier, causing an error about a name being defined multiple times. The code generation does not try to resolve such collisions automatically, as this would likely cause confusion about which identifier refers to which file. Instead, you need to rename any affected paths (but if you have no use for the generated identifiers, you can just disable them with template.identifiers = false).

Default: true

See example.


A macro name used to instantiate the asset type per file.

As inputs, the macro is passed the following arguments, separated by comma:

  1. Relative file path as a string literal. Path components are separated by /.
  2. Absolute file path as a string literal.

As an output, the macro must return a constant expression.

Default: A default initializer is constructed by recognizing standard fields.

See example.

template visitors

This is the most flexible customization of the code generation process.

Essentially, a visitor transforms the tree of selected files into code. It does so by calling custom macros at these levels:

  • For the base folder, a visit_base macro is called to wrap everything (top level).
  • For each folder, a visit_folder macro is called, wrapping the code generated from its files and subfolders (recursively).
  • For each file, a visit_file macro is called (bottom level).

These macros are passed the following inputs, separated by comma:

  • visit_base:
    1. Total number of selected files as a usize literal.
    2. Outputs of the visitor applied to the base folder entries, ordered by filename in Unicode code point order.
  • visit_folder:
    1. Folder name as a string literal.
    2. Sanitized folder name as an identifier.
    3. Outputs of the visitor applied to the folder entries, ordered by filename in Unicode code point order.
  • visit_file:
    1. Filename as a string literal.
    2. Sanitized filename as an identifier.
    3. Zero-based index of the file among the selected files as a usize literal.
    4. Relative file path as a string literal. Path components are separated by /.
    5. Absolute file path as a string literal.

The visit_folder macro is optional. If missing, the outputs of the visit_file calls are directly passed as an input to the visit_base call. This is useful to generate flat structures such as arrays. Similarly, the visit_base macro is optional.

You can configure multiple visitors. They are applied in order.

To plug in visitors, add this to your configuration for each visitor:

visit_base = 'visit_my_base'
visit_folder = 'visit_my_folder'
visit_file = 'visit_my_file'

visit_my_… are the names of your corresponding macros.

See examples:

Further resources


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