Repository Analysis

dtolnay/cxx

Safe interop between Rust and C++

2.4 Likely human-written View on GitHub

Analysis Overview

This report presents the forensic synthetic code analysis of dtolnay/cxx, a Rust project with 6,773 GitHub stars. SynthScan v2.0 examined 31,033 lines of code across 299 source files, recording 75 pattern matches distributed across 1 syntactic category. The overall adjusted score of 2.4 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).

2.4

Adjusted Score

2.4

Raw Score

100%

Time Factor

2026-07-14

Last Push

6.8K

Stars

Rust

Language

31.0K

Lines of Code

299

Files

Pattern Hits

2026-07-14

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

This chart maps the temporal evolution of the adjusted synthetic code score across successive scan runs. An upward trajectory indicates ongoing incorporation of AI-generated code or expanding LLM-assisted scaffolding; a stable or declining trajectory may reflect active human refactoring, code removal, or the adoption of stricter authorship policies. The dashed secondary line (right axis) independently tracks total raw pattern hit count, which can diverge from the normalised score when codebase size changes significantly between scans.

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 75

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 75 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 Block75 hits · 75 pts

Severity	File	Line	Snippet	Context
LOW	bridge/lib/src/lib.rs	1	//! The CXX code generator for constructing and compiling C++ code.	COMMENT
LOW	bridge/src/write.rs	541	out.next_section();	COMMENT
LOW	bridge/src/write.rs	561	//	COMMENT
LOW	bridge/src/mod.rs	41	/// #	COMMENT
LOW	bridge/src/builtin/alignmax.h	1	#pragma once	COMMENT
LOW	include/cxx.h	1	#pragma once	COMMENT
LOW	include/cxx.h	461	Opaque(const Opaque &) = delete;	COMMENT
LOW	tests/cpp_compile/mod.rs	21	/// Path to the `.cc` file (in `temp_dir`) that is generated by the	COMMENT
LOW	tests/cpp_compile/mod.rs	61	temp_dir,	COMMENT
LOW	tests/cpp_compile/mod.rs	81	///	COMMENT
LOW	tests/cpp_compile/mod.rs	161	///	COMMENT
LOW	macro/src/lib.rs	41		COMMENT
LOW	macro/src/expand.rs	1681	#cfg	COMMENT
LOW	macro/src/expand.rs	1761		COMMENT
LOW	book/src/concepts.md	21	language.	COMMENT
LOW	book/src/concepts.md	41	# unsafe extern "C++" {	COMMENT
LOW	book/src/tutorial.md	301	# fn next_chunk(buf: &mut MultiBuf) -> &[u8];	COMMENT
LOW	book/src/tutorial.md	381		COMMENT
LOW	book/src/tutorial.md	401	# unsafe extern "C++" {	COMMENT
LOW	book/src/tutorial.md	521	# fn next_chunk(buf: &mut MultiBuf) -> &[u8];	COMMENT
LOW	syntax/mangle.rs	1	// Mangled symbol arrangements:	COMMENT
LOW	syntax/mangle.rs	21	// - cxxbridge1$unique_ptr$std$vector$u8$drop	COMMENT
LOW	syntax/mangle.rs	41	// pattern: {NAMESPACE...} $ {CXXBRIDGE} $ {CXXVERSION} $ {TYPE} $ operator $ {NAME}	COMMENT
LOW	syntax/attrs.rs	1	use crate::syntax::cfg::CfgExpr;	COMMENT
LOW	syntax/instantiate.rs	21	///	COMMENT
LOW	src/lib.rs	1	//! [![github]](https://github.com/dtolnay/cxx)&ensp;[![crates-io]](https://crates.io/crates/cxx)&ensp;[![docs-rs]](http	COMMENT
LOW	src/lib.rs	21	//! Compiler support: requires rustc 1.85+ and c++11 or newer<br>	COMMENT
LOW	src/lib.rs	41	//! If everything checks out statically, then CXX uses a pair of code generators	COMMENT
LOW	src/lib.rs	61	//! string from C++, its `size()` member function calls Rust's `len()`.	COMMENT
LOW	src/lib.rs	81	//! // Any shared structs, whose fields will be visible to both languages.	COMMENT
LOW	src/lib.rs	101	//!	COMMENT
LOW	src/lib.rs	121	//! ```	COMMENT
LOW	src/lib.rs	141	//!	COMMENT
LOW	src/lib.rs	161	//! type depending on your use case.	COMMENT
LOW	src/lib.rs	181	//! Your function implementations themselves, whether in C++ or Rust, do not	COMMENT
LOW	src/lib.rs	201	//! replacement for the concept of `extern "C"` signatures as we know them,	COMMENT
LOW	src/lib.rs	221	//! of your FFI that is straightforward and doing the remaining few oddball	COMMENT
LOW	src/lib.rs	241	//! ```toml	COMMENT
LOW	src/lib.rs	261	//!	COMMENT
LOW	src/lib.rs	281	//!	COMMENT
LOW	src/lib.rs	301	//! may contain internal pointers that would be screwed up by Rust's move	COMMENT
LOW	src/lib.rs	321	//! <br>	COMMENT
LOW	src/lib.rs	341	//! <tr><td><a href="struct.CxxVector.html">CxxVector<T></a></td><td>std::vector<T></td><td><sup><i>cannot b	COMMENT
LOW	src/cxx_string.rs	21	fn string_init(this: &mut MaybeUninit<CxxString>, ptr: *const u8, len: usize);	COMMENT
LOW	src/cxx_string.rs	41	/// macro, in Rust code we can never obtain a `CxxString` by value. C++'s string	COMMENT
LOW	src/cxx_string.rs	61	/// ```	COMMENT
LOW	src/cxx_string.rs	101	/// [`let_cxx_string!`] macro.	COMMENT
LOW	src/cxx_string.rs	121	self.len() == 0	COMMENT
LOW	src/cxx_string.rs	141	///	COMMENT
LOW	src/cxx_string.rs	161		COMMENT
LOW	src/cxx_string.rs	181	///	COMMENT
LOW	src/cxx_string.rs	201	/// **The meaning of the argument is not the same as	COMMENT
LOW	src/shared_ptr.rs	21	/// WARNING: Unlike Rust's `Arc<T>`, a C++ shared pointer manipulates	COMMENT
LOW	src/shared_ptr.rs	81	shared_ptr.assume_init()	COMMENT
LOW	src/shared_ptr.rs	101	/// Panics if `T` is an incomplete type (including `void`) or is not	COMMENT
LOW	src/shared_ptr.rs	121	///	COMMENT
LOW	src/shared_ptr.rs	141	///	COMMENT
LOW	src/shared_ptr.rs	161	/// # Panics	COMMENT
LOW	src/shared_ptr.rs	361	///	COMMENT
LOW	src/cxx_vector.rs	41	/// Constructs a new heap allocated vector, wrapped by UniquePtr.	COMMENT
15 more matches not shown…