1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134

use proc_macro2::*;
use quote::{ToTokens, TokenStreamExt};
use syn::parse::Error;

/// Provide a Diagnostic with the given span and message
#[macro_export]
macro_rules! err_span {
    ($span:expr, $($msg:tt)*) => (
        $crate::Diagnostic::spanned_error(&$span, format!($($msg)*))
    )
}

/// Immediately fail and return an Err, with the arguments passed to err_span!
#[macro_export]
macro_rules! bail_span {
    ($($t:tt)*) => (
        return Err(err_span!($($t)*).into())
    )
}

/// A struct representing a diagnostic to emit to the end-user as an error.
#[derive(Debug)]
pub struct Diagnostic {
    inner: Repr,
}

#[derive(Debug)]
enum Repr {
    Single {
        text: String,
        span: Option<(Span, Span)>,
    },
    SynError(Error),
    Multi {
        diagnostics: Vec<Diagnostic>,
    },
}

impl Diagnostic {
    /// Generate a `Diagnostic` from an informational message with no Span
    pub fn error<T: Into<String>>(text: T) -> Diagnostic {
        Diagnostic {
            inner: Repr::Single {
                text: text.into(),
                span: None,
            },
        }
    }

    /// Generate a `Diagnostic` from a Span and an informational message
    pub fn span_error<T: Into<String>>(span: Span, text: T) -> Diagnostic {
        Diagnostic {
            inner: Repr::Single {
                text: text.into(),
                span: Some((span, span)),
            },
        }
    }

    /// Generate a `Diagnostic` from the span of any tokenizable object and a message
    pub fn spanned_error<T: Into<String>>(node: &dyn ToTokens, text: T) -> Diagnostic {
        Diagnostic {
            inner: Repr::Single {
                text: text.into(),
                span: extract_spans(node),
            },
        }
    }

    /// Attempt to generate a `Diagnostic` from a vector of other `Diagnostic` instances.
    /// If the `Vec` is empty, returns `Ok(())`, otherwise returns the new `Diagnostic`
    pub fn from_vec(diagnostics: Vec<Diagnostic>) -> Result<(), Diagnostic> {
        if diagnostics.is_empty() {
            Ok(())
        } else {
            Err(Diagnostic {
                inner: Repr::Multi { diagnostics },
            })
        }
    }

    /// Immediately trigger a panic from this `Diagnostic`
    #[allow(unconditional_recursion)]
    pub fn panic(&self) -> ! {
        match &self.inner {
            Repr::Single { text, .. } => panic!("{}", text),
            Repr::SynError(error) => panic!("{}", error),
            Repr::Multi { diagnostics } => diagnostics[0].panic(),
        }
    }
}

impl From<Error> for Diagnostic {
    fn from(err: Error) -> Diagnostic {
        Diagnostic {
            inner: Repr::SynError(err),
        }
    }
}

fn extract_spans(node: &dyn ToTokens) -> Option<(Span, Span)> {
    let mut t = TokenStream::new();
    node.to_tokens(&mut t);
    let mut tokens = t.into_iter();
    let start = tokens.next().map(|t| t.span());
    let end = tokens.last().map(|t| t.span());
    start.map(|start| (start, end.unwrap_or(start)))
}

impl ToTokens for Diagnostic {
    fn to_tokens(&self, dst: &mut TokenStream) {
        match &self.inner {
            Repr::Single { text, span } => {
                let cs2 = (Span::call_site(), Span::call_site());
                let (start, end) = span.unwrap_or(cs2);
                dst.append(Ident::new("compile_error", start));
                dst.append(Punct::new('!', Spacing::Alone));
                let mut message = TokenStream::new();
                message.append(Literal::string(text));
                let mut group = Group::new(Delimiter::Brace, message);
                group.set_span(end);
                dst.append(group);
            }
            Repr::Multi { diagnostics } => {
                for diagnostic in diagnostics {
                    diagnostic.to_tokens(dst);
                }
            }
            Repr::SynError(err) => {
                err.to_compile_error().to_tokens(dst);
            }
        }
    }
}