rustc_macros/diagnostics/
error.rs

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1use proc_macro::{Diagnostic, Level, MultiSpan};
2use proc_macro2::TokenStream;
3use quote::quote;
4use syn::spanned::Spanned;
5use syn::{Attribute, Error as SynError, Meta};
6
7#[derive(Debug)]
8pub(crate) enum DiagnosticDeriveError {
9    SynError(SynError),
10    ErrorHandled,
11}
12
13impl DiagnosticDeriveError {
14    pub(crate) fn to_compile_error(self) -> TokenStream {
15        match self {
16            DiagnosticDeriveError::SynError(e) => e.to_compile_error(),
17            DiagnosticDeriveError::ErrorHandled => {
18                // Return ! to avoid having to create a blank Diag to return when an
19                // error has already been emitted to the compiler.
20                quote! {
21                    { unreachable!(); }
22                }
23            }
24        }
25    }
26}
27
28impl From<SynError> for DiagnosticDeriveError {
29    fn from(e: SynError) -> Self {
30        DiagnosticDeriveError::SynError(e)
31    }
32}
33
34/// Helper function for use with `throw_*` macros - constraints `$f` to an `impl FnOnce`.
35pub(crate) fn _throw_err(
36    diag: Diagnostic,
37    f: impl FnOnce(Diagnostic) -> Diagnostic,
38) -> DiagnosticDeriveError {
39    f(diag).emit();
40    DiagnosticDeriveError::ErrorHandled
41}
42
43/// Helper function for printing `syn::Path` - doesn't handle arguments in paths and these are
44/// unlikely to come up much in use of the macro.
45fn path_to_string(path: &syn::Path) -> String {
46    let mut out = String::new();
47    for (i, segment) in path.segments.iter().enumerate() {
48        if i > 0 || path.leading_colon.is_some() {
49            out.push_str("::");
50        }
51        out.push_str(&segment.ident.to_string());
52    }
53    out
54}
55
56/// Returns an error diagnostic on span `span` with msg `msg`.
57#[must_use]
58pub(crate) fn span_err<T: Into<String>>(span: impl MultiSpan, msg: T) -> Diagnostic {
59    Diagnostic::spanned(span, Level::Error, format!("derive(Diagnostic): {}", msg.into()))
60}
61
62/// Emit a diagnostic on span `$span` with msg `$msg` (optionally performing additional decoration
63/// using the `FnOnce` passed in `diag`) and return `Err(ErrorHandled)`.
64///
65/// For methods that return a `Result<_, DiagnosticDeriveError>`:
66macro_rules! throw_span_err {
67    ($span:expr, $msg:expr) => {{ throw_span_err!($span, $msg, |diag| diag) }};
68    ($span:expr, $msg:expr, $f:expr) => {{
69        let diag = span_err($span, $msg);
70        return Err(crate::diagnostics::error::_throw_err(diag, $f));
71    }};
72}
73
74pub(crate) use throw_span_err;
75
76/// Returns an error diagnostic for an invalid attribute.
77pub(crate) fn invalid_attr(attr: &Attribute) -> Diagnostic {
78    let span = attr.span().unwrap();
79    let path = path_to_string(attr.path());
80    match attr.meta {
81        Meta::Path(_) => span_err(span, format!("`#[{path}]` is not a valid attribute")),
82        Meta::NameValue(_) => span_err(span, format!("`#[{path} = ...]` is not a valid attribute")),
83        Meta::List(_) => span_err(span, format!("`#[{path}(...)]` is not a valid attribute")),
84    }
85}
86
87/// Emit an error diagnostic for an invalid attribute (optionally performing additional decoration
88/// using the `FnOnce` passed in `diag`) and return `Err(ErrorHandled)`.
89///
90/// For methods that return a `Result<_, DiagnosticDeriveError>`:
91macro_rules! throw_invalid_attr {
92    ($attr:expr) => {{ throw_invalid_attr!($attr, |diag| diag) }};
93    ($attr:expr, $f:expr) => {{
94        let diag = crate::diagnostics::error::invalid_attr($attr);
95        return Err(crate::diagnostics::error::_throw_err(diag, $f));
96    }};
97}
98
99pub(crate) use throw_invalid_attr;
rustc_macros/diagnostics/error.rs

rustc_macros/diagnostics/
error.rs
