#lifetime #timeline #borrowing #interactive #ownership #events #tools #generate

app rustviz

A tool that allows teachers to generate an interactive timeline depicting ownership and borrowing events for each variable in a Rust code example

1 unstable release

0.1.0 May 13, 2022

#49 in Visualization

MIT license

6.5K SLoC

Rust 3.5K SLoC // 0.2% comments JavaScript 3K SLoC // 0.1% comments Shell 81 SLoC // 0.2% comments


Build Status

RustViz is a tool that generates interactive visualizations from simple Rust programs to assist users in better understanding the Rust Lifetime and Borrowing mechanism.

RustViz is a project of the Future of Programming Lab at the University of Michigan.

What does it look like?

RustViz generates SVG files with graphical indicators that integrate with mdbook to render interactive visualizations of ownership and borrowing related events in a Rust program. Here's a sample view of what a visualization can look like:

alt tag

You can read more about it in our draft paper. Note that the section on generating visualizations is out of date, see below.


RustViz is capable of generating visualizations for simple Rust programs (albeit with certain limitations) that have been annotated by the user. We are not currently attempting to generate visualizations automatically. In this section, we'll showcase how to generate SVG renderings of examples provided by us.

RustViz requires Rust, Cargo and mdbook to be installed. Once you have installed all the above prerequisites, direct into /rustviz_mdbook and run the script:

~/rustviz/rustviz_mdbook$ ./view_examples.sh

You may have an output similar to this:

Generating visualizations for the following examples:
building copy...
building hatra1...
building hatra2...
building func_take_ownership...
building func_take_return_ownership...
2021-01-19 12:36:13 [INFO] (mdbook::book): Book building has started
2021-01-19 12:36:13 [INFO] (mdbook::book): Running the html backend
Serving HTTP on :: port 8000 (http://[::]:8000/) ...

If you observed this output, then you have successfully generated the Rust visualization examples! Now open your browser and navigate to http://localhost:8000/. You should be able to view the examples individually by selecting them from the left side bar. To view the visualization, click the toggle button on the top right corner of the code block.

Great, this is how you can generate and view visualizations created using RustViz. Now let's create one from scratch!

Step-By-Step Guide

In this section, we'll dive into creating an example, string_from_move_print. First, take note of the file structure we'll need to run the example:

├── input
   └── annotated_source.rs
└── source.rs

source.rs contains the untouched source code we wish to render into an image:

fn main() {
    let x = String::from("hello");
    let y = x;
    println!("{}", y);

In this example, String::from() moves a string ("hello") to x, then x's resource is moved to y. Subsequently, println!() outputs a message to io::stdout without moving the resource.

Next, let's familiarize ourselves with the syntax used in main.rs. The RustViz tool defines all possible owners, references or input of any memory resource as a ResourceAccessPoint. In this case, we consider the function String::from() and two variables, x and y, as Resource Access Points (RAPs). Each of String::from() and x/y corresponds to RAPs ResourceAccessPoint::Function and ResourceAccessPoint::Owner, respectively.

In main.rs, we define these RAPs between the BEGIN and END comments on lines 1 and 2:

/*--- BEGIN Variable Definitions ---
Owner x; Owner y;
Function String::from();
--- END Variable Definitions ---*/

The definition header now can be automatically generated by running the view_examples.sh once. If any incorrect information appeared at the generated header, you could manully edit it by refering to the following documentation.

The format for each ResourceAccessPoint enum is shown below, where fields preceded by ':' denote an optional field:

ResourceAccessPoint Usage --
    Owner <:mut> <name>
    MutRef <:mut> <name>
    StaticRef <:mut> <name>
    Struct <:mut> <name>{<:mut> <member_1>, <:mut> <member_2>, ... }
    Function <name>

Alternatively, some code let mut a = 5; and let b = &a; would correspond to Owner mut a and StaticRef b, respectively. An immutable instance of some struct with member variables x and mut y, on the other hand, may be annotated as Struct a{x, mut y}.

It is important to note:

  1. all definitions must lie between BEGIN and END
  2. all definitions must be defined in the same order by which they were declared in the source code
  3. all definitions must be separated by a singular semicolon
  4. each field within a RAP definition must be separated by a whitespace

After running the view_examples.sh once we should have the following file structure:

├── input
   └── annotated_source.rs
├── main.rs
└── source.rs

Next, we annotate the code with the use of ExternalEvents that describe move, borrow, and drop semantics of Rust. In string_from_move_print, we have four such events:

  1. Move of resource from String::from() to x
  2. Move of resource from y to x
  3. Drop of resource binded to x
  4. Drop of resource binded to y

We can specify Events in structured comments like so:

/* --- BEGIN Variable Definitions ---
Owner x; Owner y;
Function String::from();
 --- END Variable Definitions --- */
fn main() {
    let x = String::from("hello"); // !{ Move(String::from()->x) }
    let y = x; // !{ Move(x->y) }
    println!("{}", y); // print to stdout!
} /* !{
} */

Each Event is defined on the line where it occurs and within delimiters !{ and }.

Events can be annotated within block comments; however, the block must start on the line in which the events occur. Additionally, all Events within a !{} delimitation must be separated by a singular comma and must each follow the format:

ExternalEvents Usage:
    Format: <event_name>(<from>-><to>)
        e.g.: // !{ PassByMutableReference(a->Some_Function()), ... }
    Note: GoOutOfScope and InitRefParam require only the <from> parameter
        e.g.: // !{ GoOutOfScope(x) }

Refer to the Appendix for a list of usable ExternalEvent's.

Phew! All that's left is running the program. Simply navigate into src and run:

cargo run string_from_move_print

Now your folder should look like this:

├── input
│   └── annotated_source.rs
├── main.rs
├── source.rs
├── vis_code.svg
└── vis_timeline.svg

Congratulations! You have successfully generated your first visualization! As a last step, add the name of your example to targetExamples under view_examples.sh and run the script from rustviz_mdbook to see it in your browser.


ExternalEvent Usage:

Event Usage
Bind(a) Let binding or assignment.
e.g.: let a = 1;
Copy(a->b) Copies the resource of a to variable b. Here, a implements the Copy trait.
Move(a->b) Moves the resource of a to variable b. Here, a implements the Move trait.
Note: Moving to None (i.e.: Move(a->None)) is used to express a move to the caller function.
StaticBorrow(a->b) Assigns an immutable reference of a to b.
e.g.: let b = &a;
MutableBorrow(a->b) Assigns a mutable reference of a to b.
e.g.: let b = &mut a;
StaticDie(a->b) Ends the non-lexical lifetime of the reference variable a and returns the resource back to its owner b.
MutableDie(a->b) Ends the non-lexical lifetime of the reference variable a and returns the resource back to its owner b.
PassByStaticReference(a->b) Passes an immutable reference of variable a to function b. Not to be confused with StaticBorrow.
PassByMutableReference(a->b) Passes a mutable reference of variable a to function b. Not to be confused with MutableBorrow.
GoOutOfScope(a) Ends the lexical lifetime of variable a.
InitRefParam(a) Initializes the parameter a of some function, which is a reference.
e.g.: some_fn(a: &String) {..}
InitOwnerParam(a) Initializes the parameter a of some function, which owns the resource.
e.g.: some_fn(a: String) {..}


  1. GoOutOfScope, InitRefParam and InitOwnerParam require a singular parameter previously defined in the Variable Definitions section. (e.g.: // !{ GoOutOfScope(x) })
  2. All other events require two parameters, a and b, which can either be defined (e.g.: Owner a) or undefined (None).

The None type can be used as the <to> parameter (e.g.: Move(a->None)) to specify a move to the function caller.

  1. All uses of Struct fields must be preceded by its parent struct's name. (e.g.: a.b = 1; can be annotated as Move(None->a.b), where a is the parent and b is the field.)

Visualization Limitations

Some features are still being built. As of now, we are limited to:

  • No branching logic
  • No looping
  • No explicit lifetime annotation