Repository Analysis

dtolnay/syn

Parser for Rust source code

3.5 Likely human-written View on GitHub

Analysis Overview

This report presents the forensic synthetic code analysis of dtolnay/syn, a Rust project with 3,398 GitHub stars. SynthScan v2.0 examined 78,939 lines of code across 161 source files, recording 304 pattern matches distributed across 1 syntactic category. The overall adjusted score of 3.5 places this repository in the Likely human-written band.

The scanner applied 160+ deterministic lexical heuristics, multi-line block detectors, abstract syntax tree depth profilers, and a cross-file Jaccard similarity matrix to construct a statistically normalised synthetic code estimate. All matches are individually weighted by severity coefficient and contextual multiplier before summation, and the resulting headline score is temporally discounted to account for the repository's development history relative to the commercial emergence of large language model coding tooling (November 2022 onward).

3.5

Adjusted Score

3.5

Raw Score

100%

Time Factor

2026-07-25

Last Push

3.4K

Stars

Rust

Language

78.9K

Lines of Code

161

Files

304

Pattern Hits

2026-08-02

Scan Date

0.00

HC Hit Rate

What These Metrics Mean

Adjusted Score: Primary synthetic code indicator. Raw score normalised per 1,000 lines of code and multiplied by the temporal discount factor. This is the definitive comparative metric — use it to rank repositories by AI authorship density.
Raw Score: The unmodified sum of all severity-weighted, context-multiplied pattern match scores before temporal discounting. Reflects the absolute signal strength independent of when the repository was last active.
Time Factor: The temporal discount multiplier (0–100%) applied to the raw score. Repositories last updated before ChatGPT's launch (Nov 2022) receive a 5% factor. Full signal is only assigned to repositories active in the post-adoption era (Jan 2024+).
Pattern Hits: Total count of individual pattern matches across all files and categories. A high hit count with a low score may indicate a very large codebase with isolated AI snippets; a low count with a high score indicates dense, concentrated AI signatures.
HC Hit Rate: High+Critical pattern hits per file, averaged across the repository. This orthogonal signal catches repositories where a few files are densely packed with high-severity AI tells — a strong indicator even when the normalised score appears moderate due to codebase size.
Lines of Code / Files: Total lines and files analysed. The scanner examines 94 file extensions. These denominators are used to normalise the score, enabling fair comparison between repositories of vastly different sizes.

Score History

Longitudinal tracking requires multiple scan runs. Once this repository is re-scanned after new commits land, this chart will visualise how the synthetic code signal evolves over time — enabling you to detect whether AI authorship is growing, stabilising, or being actively corrected by human engineers.

No multi-scan history yet — run the scanner again to build trend data.

Severity Breakdown

Classifies detected patterns by their diagnostic confidence and structural impact. CRITICAL patterns (coefficient 10) represent definitive synthetic signatures — hallucinated imports, explicit LLM attribution metadata — virtually never produced by human authors. HIGH (5) indicates strong structural tells such as cross-file repetition or cross-linguistic idioms. MEDIUM (2) covers recognisable conversational padding and AI-specific vocabulary. LOW (1) captures subtle indicators like tautological comments and generic boilerplate that require density to carry independent signal.

CRITICAL 0HIGH 0MEDIUM 0LOW 304

Directory Score Breakdown

This horizontal bar chart decomposes the repository's raw synthetic code score by top-level directory, allowing you to pinpoint precisely which modules or components carry the highest AI authorship density. Directories with disproportionately high scores relative to their size warrant targeted manual review: concentrated AI signatures often trace back to mass-generated configuration layers, auto-ported test suites, LLM-scaffolded boilerplate classes, or entire subsystems authored under heavy copilot assistance. Use this view to prioritise your human code-review effort.

Pattern Findings

The scanner identified 304 distinct pattern matches across 1 syntactic category. Each entry below represents a discrete location in the source code where the engine recorded a statistically significant AI authorship indicator. Expand any category row to inspect the individual file paths, line numbers, code snippets, and the lexical context (CODE, COMMENT, or STRING) in which each match was detected.

Reading the findings table: The Severity column indicates the diagnostic confidence level (CRITICAL / HIGH / MEDIUM / LOW). The Context column identifies whether the match occurred inside executable code, an inline comment, or a string literal — comment-context matches receive a ×1.5 weight because LLMs systematically over-annotate. The ⚡ bolt icon marks clustered matches: three or more patterns within a 10-line window, each receiving an additional ×1.5 density multiplier as dense clusters constitute far stronger evidence of synthetic authorship than isolated hits.

Over-Commented Block304 hits · 278 pts

Severity	File	Line	Snippet	Context
LOW	tests/test_precedence.rs	1	// This test does the following for every file in the rust-lang/rust repo:	COMMENT
LOW	tests/test_expr.rs	1001	// Expr::Binary	COMMENT
LOW	codegen/src/main.rs	1	// This crate crawls the Syn source directory to find all structs and enums that	COMMENT
LOW	json/src/lib.rs	1	//! # Data structures that describe Syn's syntax tree.	COMMENT
LOW	json/src/lib.rs	21	//! every Syn release comes with a machine-readable description of that version	COMMENT
LOW	json/src/lib.rs	41	//! for node in &defs.types {	COMMENT
LOW	json/src/lib.rs	61	/// The Syn version whose syntax tree is described by this data.	COMMENT
LOW	json/src/lib.rs	121	}	COMMENT
LOW	json/src/lib.rs	141	serde(rename_all = "lowercase")	COMMENT
LOW	json/src/lib.rs	161		COMMENT
LOW	examples/lazy-static/lazy-static/src/lib.rs	1	#![feature(proc_macro_diagnostic)]	COMMENT
LOW	examples/lazy-static/lazy-static/src/lib.rs	81	init.span()	COMMENT
LOW	examples/dump-syntax/src/main.rs	1	//! Parse a Rust source file into a `syn::File` and print out a debug	COMMENT
LOW	examples/trace-var/trace-var/src/lib.rs	61	///	COMMENT
LOW	examples/trace-var/trace-var/src/lib.rs	161	/// Attribute to print the value of the given variables each time they are	COMMENT
LOW	src/lit.rs	21	use proc_macro2::{TokenStream, TokenTree};	COMMENT
LOW	src/lit.rs	161	///	COMMENT
LOW	src/lit.rs	181	/// }	COMMENT
LOW	src/lit.rs	201	/// ```	COMMENT
LOW	src/lit.rs	441	pub fn base10_digits(&self) -> &str {	COMMENT
LOW	src/custom_keyword.rs	1	/// Define a type that supports parsing and printing a given identifier as if it	COMMENT
LOW	src/custom_keyword.rs	21	/// - [Parsing] — `input.parse::<kw::whatever>()?`	COMMENT
LOW	src/custom_keyword.rs	41	/// The symbols `bool` and `str` are not reserved keywords in Rust so these are	COMMENT
LOW	src/custom_keyword.rs	61	/// Str {	COMMENT
LOW	src/custom_keyword.rs	81	/// value: input.parse()?,	COMMENT
LOW	src/punctuated.rs	1	//! A punctuated sequence of syntax tree nodes separated by punctuation.	COMMENT
LOW	src/punctuated.rs	161	/// punctuated pairs.	COMMENT
LOW	src/punctuated.rs	301	#[cfg(feature = "parsing")]	COMMENT
LOW	src/punctuated.rs	1001	Pair::Punctuated(_, p) => Some(p),	COMMENT
LOW	src/custom_punctuation.rs	1	/// Define a type that supports parsing and printing a multi-character symbol	COMMENT
LOW	src/custom_punctuation.rs	21	/// - Construction from multiple [`Span`] — `let lrarrow = LeftRightArrow([sp, sp, sp])`	COMMENT
LOW	src/custom_punctuation.rs	41	/// // expr </> expr </> expr ...	COMMENT
LOW	src/custom_punctuation.rs	61	/// }	COMMENT
LOW	src/stmt.rs	61	///	COMMENT
LOW	src/stmt.rs	141	///	COMMENT
LOW	src/stmt.rs	161	/// }	COMMENT
LOW	src/error.rs	21	pub type Result<T> = core::result::Result<T, Error>;	COMMENT
LOW	src/error.rs	41	/// #	COMMENT
LOW	src/error.rs	61	/// }	COMMENT
LOW	src/error.rs	81	/// # extern crate proc_macro;	COMMENT
LOW	src/error.rs	101	/// #	COMMENT
LOW	src/error.rs	141	///	COMMENT
LOW	src/error.rs	181	/// Creates an error with the specified message spanning the given syntax	COMMENT
LOW	src/error.rs	221	/// use syn::parse::{Error, ParseStream, Result};	COMMENT
LOW	src/error.rs	241	/// }	COMMENT
LOW	src/error.rs	301		COMMENT
LOW	src/error.rs	321	/// # Example	COMMENT
LOW	src/token.rs	1	//! Tokens representing Rust punctuation, keywords, and delimiters.	COMMENT
LOW	src/token.rs	21	//! pub static_token: Token![static],	COMMENT
LOW	src/token.rs	41	//! [`braced!`]: crate::braced!	COMMENT
LOW	src/token.rs	61	//! ty: input.parse()?,	COMMENT
LOW	src/token.rs	81	//!	COMMENT
LOW	src/token.rs	821	/// use syn::{Ident, Token};	COMMENT
LOW	src/token.rs	841	/// As an expression, `Token!` is used for peeking tokens or instantiating	COMMENT
LOW	src/token.rs	861	/// let span = name.span();	COMMENT
LOW	src/parse_macro_input.rs	1	/// Parse the input TokenStream of a macro, triggering a compile error if the	COMMENT
LOW	src/parse_macro_input.rs	21	/// use proc_macro::TokenStream;	COMMENT
LOW	src/parse_macro_input.rs	41	///	COMMENT
LOW	src/parse_macro_input.rs	61	/// # use syn::parse::ParseStream;	COMMENT
LOW	src/parse_macro_input.rs	81	/// ```	COMMENT
244 more matches not shown…