Crate diag_lang 

diag_lang

The diagnostics layer of a compiler front-end: it collects diagnostics — a severity, a message, and a labelled span — and renders them with source context, drawing a caret underline exactly under the characters at fault, in the style developers expect from a modern toolchain.

It owns presentation only. A lexer, parser, or type checker decides what is wrong and builds a Diagnostic; diag-lang decides how it looks. Positions come from span_lang and source text from source_lang: a Label points with a Span in a SourceMap’s global position space, and the Renderer resolves that span back to a file, a line, and a column.

Alignment

The caret line is aligned in display columns, not bytes: a multi-byte UTF-8 character counts as one column, and a tab advances to the next tab stop. The same diagnostic always renders byte-identical output, and a span that falls outside the loaded sources renders a defined note rather than panicking.

Quickstart

use diag_lang::{Diagnostic, Label, Renderer, Severity};
use diag_lang::{SourceMap, Span};

let mut map = SourceMap::new();
map.add("main.rs", "fn main() {\n    let x = foo();\n}\n").expect("fits");

let diag = Diagnostic::new(
    Severity::Error,
    "cannot find value `foo` in this scope",
    Label::new(Span::new(24, 27), "not found in this scope"),
);

let rendered = Renderer::new().render(&diag, &map);
assert!(rendered.contains("^^^ not found in this scope"));

Output

Renderer::render returns a String; Renderer::render_to writes into any core::fmt::Write sink, so the same renderer feeds a terminal, a reused buffer, or a formatter without an intermediate allocation. With the color feature, Renderer::with_color wraps the output in ANSI styling; the plain output is complete and identically aligned, so colour only ever adds.

Features

• std (default) — the standard library; without it the crate is no_std (it always needs alloc). Forwards to span-lang/std and source-lang/std.
• color (default) — ANSI styling via Renderer::with_color. Disable it, or simply never call with_color, for plain output.

Stability

The public API is stable as of 1.0 and follows Semantic Versioning: no breaking changes before 2.0, additions arrive in minor releases, and the MSRV (Rust 1.85) only rises in a minor. The full surface is catalogued in docs/API.md.

Structs

Diagnostic

One thing a compiler stage has to say about the source: a Severity, a headline message, a primary Label pointing at the span it concerns, and optionally secondary labels for related locations and trailing note/help lines.

Label

A Span plus the text that explains what is at that span.

Renderer

Renders a Diagnostic against a SourceMap into aligned, caret-annotated text in the style of a modern toolchain.

SourceMap

A collection of sources laid out end to end in a single global position space.

Span

A half-open byte range start..end into a single source.

Enums

Severity

The level a diagnostic reports at — how serious it is and how it is labelled.