Struct CallGraphBuilder 

pub struct CallGraphBuilder<'a> { /* private fields */ }

Builds a call graph by recursively tracing function calls.

Rust Book Reference

Chapter 10.3: Validating References with Lifetimes https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html

Educational Notes - Lifetime Parameters

This struct demonstrates explicit lifetime annotations:

pub struct CallGraphBuilder<'a> {
    finder: &'a mut FunctionFinder,
    extractor: &'a CallExtractor,
}

What does <'a> mean?

• 'a is a lifetime parameter (read as “lifetime a”)
• It says: “This struct holds references that live for lifetime ’a”
• The struct cannot outlive the data it references

Why do we need lifetimes here?

• CallGraphBuilder stores references to FunctionFinder and CallExtractor
• Without lifetimes, Rust doesn’t know how long these references are valid
• The lifetime 'a connects the struct’s lifetime to its references

What does this prevent?

let builder = {
    let finder = FunctionFinder::new(...);
    let extractor = CallExtractor::new(...);
    CallGraphBuilder::new(..., &mut finder, &extractor)
}; // ERROR! finder and extractor are dropped here
// builder would have dangling references!

The lifetime constraint:

• CallGraphBuilder<'a> can only exist while finder and extractor exist
• Rust enforces this at compile time
• No runtime overhead - pure compile-time safety

Alternative without lifetimes:

• Could use Box<FunctionFinder> (heap allocation + ownership)
• Could use Rc<RefCell<FunctionFinder>> (reference counting + runtime checks)
• Lifetimes are zero-cost: no allocation, no runtime checks

Implementations

impl<'a> CallGraphBuilder<'a>

pub fn new( direction: TraceDirection, max_depth: usize, finder: &'a mut FunctionFinder, extractor: &'a CallExtractor, ) -> Self

Create a new CallGraphBuilder.

Rust Book Reference

Chapter 10.3: Lifetime Annotations in Function Signatures https://doc.rust-lang.org/book/ch10-03-lifetime-syntax.html#lifetime-annotations-in-function-signatures

Educational Notes - Lifetime in Function Signatures

This function signature shows how lifetimes flow through constructors:

pub fn new(
    finder: &'a mut FunctionFinder,
    extractor: &'a CallExtractor,
) -> Self

What this means:

• The returned CallGraphBuilder<'a> contains references with lifetime 'a
• Those references come from the input parameters
• The builder cannot outlive finder or extractor

Lifetime elision: Without the struct’s <'a>, we’d need to write:

pub fn new<'a>(
    finder: &'a mut FunctionFinder,
    extractor: &'a CallExtractor,
) -> CallGraphBuilder<'a>

But since the struct already has <'a>, we can use Self.

Arguments

• direction - Whether to trace forward or backward
• max_depth - Maximum depth of the call tree
• finder - Service to find function definitions
• extractor - Service to extract calls from code

pub fn build_trace( &mut self, start_fn: &FunctionDef, ) -> Result<Option<CallTree>>

Build a call trace tree starting from the given function