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LLMs are writing significant amounts of code today. The bottleneck is no longer code generation, it is code review. Modern LLMs are highly accurate at code analysis when given proper context. The challenge is providing them with complete information about function dependencies and call relationships across the entire codebase. This blog focuses on solving that specific problem: how to give LLMs comprehensive context about code dependencies. We’ll explore how we built a call-graph system that maps function relationships accurately.

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Why RAG is not the primary component

Code has inherent structural relationships — functions call other functions, modules import dependencies, classes inherit from parents. These relationships are explicit and deterministic. When reviewing code, we need to traverse these exact relationships, not approximate them. rag_vs_callgraph RAG excels at semantic similarity and content retrieval where relationships are implicit or fuzzy. It can find conceptually related code snippets or documentation. However, code review requires precision: if function A calls function B, we need to know that with 100 % certainty. The reliability gap is fundamental. RAG retrieves based on embeddings and similarity scores, which can miss critical dependencies or surface false positives.

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LSP is not the answer

When developers hear “call graph,” the immediate suggestion is often “just use LSP (Language servers).” It’s an understandable reaction — LSP has revolutionized code intelligence in editors. But for production call-graph systems supporting hundreds of languages, LSP creates more problems than it solves. lsp_doesnt_scale Each language requires its own language server with its full runtime interpreter. Supporting 100 + languages means bundling 100 + language servers, each with their specific dependencies:
  • Python’s Pylsp requires a Python runtime
  • Rust analyzer needs the Rust toolchain
  • TypeScript server requires Node.js
  • Java language server needs the JDK
  • Go’s gopls requires the Go compiler
A Docker image containing all these environments quickly balloons to tens of gigabytes. The operational complexity multiplies.

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Static Call Graph

We came up with static call graph to answer all of these questions. We built our own call-graph generation system with a focus on accuracy, completeness, and language-agnostic support.

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Ctags

The key insight was to leverage an existing tool — Ctags — as a starting point. Ctags is a classic tool that indexes symbols (functions, classes, variables, etc.) in source code across many languages. However, using Ctags alone was not sufficient to build an accurate call graph. Ctags knows where things are defined, but not necessarily which one is being called in a given spot if names collide. For example, if two different modules each have a function named compute(), Ctags will happily index both definitions. If our code calls compute(), a naive lookup in the Ctags index would return both candidate definitions. ctags_accuracy Accuracy is paramount for us. Showing the wrong context (e.g., a different compute() function from another module) would be misleading and could derail the review.

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Building Our Context-Aware Call Graph

The solution emerged from combining two powerful tools: Ctags for its broad language support and tree-sitter for precise syntax analysis. Here’s how we made them work together to achieve the accuracy we needed.

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Step 1 — Creating the Symbol Universe with Ctags

We start by unleashing Ctags on the entire codebase. Within seconds, it indexes every function, class, and variable across hundreds of files — regardless of programming language. This gives us our “universe of possibilities”: every place where compute(), process(), or any other function might be defined.

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Step 2 — Finding Who’s Calling Whom

Next comes tree-sitter. While Ctags built our directory of definitions, tree-sitter reads through the code to find every function call. It understands the actual structure of the code — not just pattern matching, but real syntax trees. When it encounters result = compute(100), tree-sitter knows this is a function call, not a variable assignment or a string.

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Step 3 — The Candidate Lineup

For each function call tree-sitter finds, we query our Ctags index. This is where things get interesting. A call to compute() might return three different candidates from completely different modules. Without further analysis, we’re looking at a three-way ambiguity. This is exactly what breaks naive approaches. Some tools would just pick the first match or show all three. But in code review, precision matters — showing the wrong compute() function could lead to completely incorrect review feedback.

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Step 4 — Import Resolution

Here’s where our approach shines. We analyze the imports at the top of each file to resolve which specific function is being called. The implementation adapts to each language’s import system: ambiguity_problem
  • Python’s import trail: When we see from payment.utils import compute, we know exactly which compute() wins. Even with relative imports like from ..utils import compute, we resolve the path relative to the current file’s location.
  • JavaScript’s module maze: Whether it’s import { compute } from './payment/utils' or const { compute } = require('./analytics/metrics'), we trace through the module system. We handle default exports, named exports, and even barrel exports that re-export from other files.
  • Java’s package precision: Fully qualified calls like com.payment.Utils.compute() are obvious, but we also resolve simple compute() calls by checking the import com.payment.Utils; statements. We even handle wildcard imports, though they require checking each potential match.
  • Local scope wins: If a function is defined in the same file where it’s called, that local definition takes precedence — just like variable-scoping rules in most languages.

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Step 5 — Connecting the Dots

Once we’ve identified the correct target for each call, we build the edge in our call graph. But we don’t just store “A calls B” — we preserve rich metadata: 
{
  "caller": {
    "function": "process_payment",
    "file": "src/main.py",
    "line": 127
  },
  "callee": {
    "function": "compute",
    "file": "src/payment/utils.py",
    "line": 42
  },
  "call_site": {
    "line": 134,
    "column": 15,
    "context": "fee = compute(order.total)"
  }
}
This rich context enables the LLM to understand not just what functions are connected, but exactly how they’re used. When reviewing a change to compute(), the LLM can see every call site and understand the specific context of each usage. The beauty of this approach is its scalability. By building on Ctags’ language support, we immediately work with any language it supports — over 40 and counting. The import-resolution logic, while language-specific, follows common patterns that we can implement incrementally as needed.

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The Foundation of CodeAnt’s Intelligence

This import-aware call graph isn’t just a feature — it’s the core infrastructure that powers every CodeAnt product. By solving the fundamental problem of accurate code context, we’ve built a foundation that enables multiple advanced capabilities.