feat(related): Add related diagnostics (#68)

Fixes: #47

miette-derive/src/diagnostic.rs

@@ -7,6 +7,7 @@ use crate::diagnostic_arg::DiagnosticArg;
 use crate::forward::{Forward, WhichFn};
 use crate::help::Help;
 use crate::label::Labels;
+use crate::related::Related;
 use crate::severity::Severity;
 use crate::source_code::SourceCode;
 use crate::url::Url;
@@ -64,6 +65,7 @@ pub struct DiagnosticConcreteArgs {
     pub source_code: Option<SourceCode>,
     pub url: Option<Url>,
     pub forward: Option<Forward>,
+    pub related: Option<Related>,
 }
 
 impl DiagnosticConcreteArgs {
@@ -103,9 +105,11 @@ impl DiagnosticConcreteArgs {
         }
         let labels = Labels::from_fields(fields)?;
         let source_code = SourceCode::from_fields(fields)?;
+        let related = Related::from_fields(fields)?;
         let concrete = DiagnosticConcreteArgs {
             code,
             help,
+            related,
             severity,
             labels,
             url,
@@ -215,6 +219,7 @@ impl Diagnostic {
                         let labels_method = forward.gen_struct_method(WhichFn::Labels);
                         let source_code_method = forward.gen_struct_method(WhichFn::SourceCode);
                         let severity_method = forward.gen_struct_method(WhichFn::Severity);
+                        let related_method = forward.gen_struct_method(WhichFn::Related);
 
                         quote! {
                             impl #impl_generics miette::Diagnostic for #ident #ty_generics #where_clause {
@@ -224,6 +229,7 @@ impl Diagnostic {
                                 #labels_method
                                 #severity_method
                                 #source_code_method
+                                #related_method
                             }
                         }
                     }
@@ -249,6 +255,11 @@ impl Diagnostic {
                             .as_ref()
                             .and_then(|x| x.gen_struct())
                             .or_else(|| forward(WhichFn::Severity));
+                        let rel_body = concrete
+                            .related
+                            .as_ref()
+                            .and_then(|x| x.gen_struct())
+                            .or_else(|| forward(WhichFn::Related));
                         let url_body = concrete
                             .url
                             .as_ref()
@@ -269,6 +280,7 @@ impl Diagnostic {
                                 #code_body
                                 #help_body
                                 #sev_body
+                                #rel_body
                                 #url_body
                                 #labels_body
                                 #src_body
@@ -288,6 +300,7 @@ impl Diagnostic {
                 let sev_body = Severity::gen_enum(variants);
                 let labels_body = Labels::gen_enum(variants);
                 let src_body = SourceCode::gen_enum(variants);
+                let rel_body = Related::gen_enum(variants);
                 let url_body = Url::gen_enum(ident, variants);
                 quote! {
                     impl #impl_generics miette::Diagnostic for #ident #ty_generics #where_clause {
@@ -296,6 +309,7 @@ impl Diagnostic {
                         #sev_body
                         #labels_body
                         #src_body
+                        #rel_body
                         #url_body
                     }
                 }

miette-derive/src/forward.rs

@@ -37,6 +37,7 @@ pub enum WhichFn {
     Severity,
     Labels,
     SourceCode,
+    Related,
 }
 
 impl WhichFn {
@@ -48,6 +49,7 @@ impl WhichFn {
             Self::Severity => quote! { severity() },
             Self::Labels => quote! { labels() },
             Self::SourceCode => quote! { source_code() },
+            Self::Related => quote! { related() },
         }
     }
 
@@ -65,6 +67,9 @@ impl WhichFn {
             Self::Severity => quote! {
                 fn severity(&self) -> std::option::Option<miette::Severity>
             },
+            Self::Related => quote! {
+                fn related(&self) -> std::option::Option<std::boxed::Box<dyn std::iter::Iterator<Item = &dyn miette::Diagnostic> + '_>>
+            },
             Self::Labels => quote! {
                 fn labels(&self) -> std::option::Option<std::boxed::Box<dyn std::iter::Iterator<Item = miette::LabeledSpan> + '_>>
             },

miette-derive/src/lib.rs

@@ -10,12 +10,13 @@ mod fmt;
 mod forward;
 mod help;
 mod label;
+mod related;
 mod severity;
 mod source_code;
 mod url;
 mod utils;
 
-#[proc_macro_derive(Diagnostic, attributes(diagnostic, label, source_code))]
+#[proc_macro_derive(Diagnostic, attributes(diagnostic, source_code, label, related))]
 pub fn derive_diagnostic(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input = parse_macro_input!(input as DeriveInput);
     let cmd = match Diagnostic::from_derive_input(input) {

miette-derive/src/related.rs

@@ -0,0 +1,76 @@
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote};
+use syn::spanned::Spanned;
+
+use crate::{
+    diagnostic::{DiagnosticConcreteArgs, DiagnosticDef},
+    forward::WhichFn,
+    utils::{display_pat_members, gen_all_variants_with},
+};
+
+pub struct Related(syn::Member);
+
+impl Related {
+    pub(crate) fn from_fields(fields: &syn::Fields) -> syn::Result<Option<Self>> {
+        match fields {
+            syn::Fields::Named(named) => Self::from_fields_vec(named.named.iter().collect()),
+            syn::Fields::Unnamed(unnamed) => {
+                Self::from_fields_vec(unnamed.unnamed.iter().collect())
+            }
+            syn::Fields::Unit => Ok(None),
+        }
+    }
+
+    fn from_fields_vec(fields: Vec<&syn::Field>) -> syn::Result<Option<Self>> {
+        for (i, field) in fields.iter().enumerate() {
+            for attr in &field.attrs {
+                if attr.path.is_ident("related") {
+                    let related = if let Some(ident) = field.ident.clone() {
+                        syn::Member::Named(ident)
+                    } else {
+                        syn::Member::Unnamed(syn::Index {
+                            index: i as u32,
+                            span: field.span(),
+                        })
+                    };
+                    return Ok(Some(Related(related)));
+                }
+            }
+        }
+        Ok(None)
+    }
+
+    pub(crate) fn gen_enum(variants: &[DiagnosticDef]) -> Option<TokenStream> {
+        gen_all_variants_with(
+            variants,
+            WhichFn::Related,
+            |ident, fields, DiagnosticConcreteArgs { related, .. }| {
+                let (display_pat, _display_members) = display_pat_members(fields);
+                related.as_ref().map(|related| {
+                    let rel = match &related.0 {
+                        syn::Member::Named(ident) => ident.clone(),
+                        syn::Member::Unnamed(syn::Index { index, .. }) => {
+                            format_ident!("_{}", index)
+                        }
+                    };
+                    quote! {
+                        Self::#ident #display_pat => {
+                            std::option::Option::Some(std::boxed::Box::new(
+                                #rel.iter().map(|x| -> &(dyn Diagnostic) { &*x })
+                            ))
+                        }
+                    }
+                })
+            },
+        )
+    }
+
+    pub(crate) fn gen_struct(&self) -> Option<TokenStream> {
+        let rel = &self.0;
+        Some(quote! {
+            fn related<'a>(&'a self) -> std::option::Option<std::boxed::Box<dyn std::iter::Iterator<Item = &'a dyn miette::Diagnostic> + 'a>> {
+                std::option::Option::Some(std::boxed::Box::new(self.#rel.iter().map(|x| -> &(dyn Diagnostic) { &*x })))
+            }
+        })
+    }
+}

src/handlers/graphical.rs

@@ -102,19 +102,17 @@ impl GraphicalReportHandler {
         self.render_header(f, diagnostic)?;
         writeln!(f)?;
         self.render_causes(f, diagnostic)?;
-
-        if let Some(source) = diagnostic.source_code() {
-            if let Some(labels) = diagnostic.labels() {
-                let mut labels = labels.collect::<Vec<_>>();
-                labels.sort_unstable_by_key(|l| l.inner().offset());
-                if !labels.is_empty() {
-                    writeln!(f)?;
-                    self.render_snippets(f, source, labels)?;
-                }
-            }
-        }
-
+        self.render_snippets(f, diagnostic)?;
         self.render_footer(f, diagnostic)?;
+        self.render_related(f, diagnostic)?;
+        if let Some(footer) = &self.footer {
+            writeln!(f)?;
+            let width = self.termwidth.saturating_sub(4);
+            let opts = textwrap::Options::new(width)
+                .initial_indent("  ")
+                .subsequent_indent("  ");
+            writeln!(f, "{}", textwrap::fill(footer, opts))?;
+        }
         Ok(())
     }
 
@@ -214,63 +212,89 @@ impl GraphicalReportHandler {
                 .subsequent_indent("        ");
             writeln!(f, "{}", textwrap::fill(&help.to_string(), opts))?;
         }
-        if let Some(footer) = &self.footer {
+        Ok(())
+    }
+
+    fn render_related(
+        &self,
+        f: &mut impl fmt::Write,
+        diagnostic: &(dyn Diagnostic),
+    ) -> fmt::Result {
+        if let Some(related) = diagnostic.related() {
             writeln!(f)?;
-            let width = self.termwidth.saturating_sub(4);
-            let opts = textwrap::Options::new(width)
-                .initial_indent("  ")
-                .subsequent_indent("  ");
-            writeln!(f, "{}", textwrap::fill(footer, opts))?;
+            for rel in related {
+                write!(f, "Error: ")?;
+                self.render_header(f, rel)?;
+                writeln!(f)?;
+                self.render_causes(f, rel)?;
+                self.render_snippets(f, rel)?;
+                self.render_footer(f, rel)?;
+                self.render_related(f, rel)?;
+            }
         }
         Ok(())
     }
 
     fn render_snippets(
         &self,
         f: &mut impl fmt::Write,
-        source: &dyn SourceCode,
-        labels: Vec<LabeledSpan>,
+        diagnostic: &(dyn Diagnostic),
     ) -> fmt::Result {
-        let contents = labels
-            .iter()
-            .map(|label| source.read_span(label.inner(), self.context_lines, self.context_lines))
-            .collect::<Result<Vec<Box<dyn SpanContents<'_>>>, MietteError>>()
-            .map_err(|_| fmt::Error)?;
-        let contexts = labels.iter().cloned().zip(contents.iter()).coalesce(
-            |(left, left_conts), (right, right_conts)| {
-                let left_end = left.offset() + left.len();
-                let right_end = right.offset() + right.len();
-                if left_conts.line() + left_conts.line_count() >= right_conts.line() {
-                    // The snippets will overlap, so we create one Big Chunky Boi
-                    let new_span = LabeledSpan::new(
-                        left.label().map(String::from),
-                        left.offset(),
-                        if right_end >= left_end {
-                            // Right end goes past left end
-                            right_end - left.offset()
-                        } else {
-                            // right is contained inside left
-                            left.len()
+        if let Some(source) = diagnostic.source_code() {
+            if let Some(labels) = diagnostic.labels() {
+                let mut labels = labels.collect::<Vec<_>>();
+                labels.sort_unstable_by_key(|l| l.inner().offset());
+                if !labels.is_empty() {
+                    writeln!(f)?;
+                    let contents = labels
+                        .iter()
+                        .map(|label| {
+                            source.read_span(label.inner(), self.context_lines, self.context_lines)
+                        })
+                        .collect::<Result<Vec<Box<dyn SpanContents<'_>>>, MietteError>>()
+                        .map_err(|_| fmt::Error)?;
+                    let contexts = labels.iter().cloned().zip(contents.iter()).coalesce(
+                        |(left, left_conts), (right, right_conts)| {
+                            let left_end = left.offset() + left.len();
+                            let right_end = right.offset() + right.len();
+                            if left_conts.line() + left_conts.line_count() >= right_conts.line() {
+                                // The snippets will overlap, so we create one Big Chunky Boi
+                                let new_span = LabeledSpan::new(
+                                    left.label().map(String::from),
+                                    left.offset(),
+                                    if right_end >= left_end {
+                                        // Right end goes past left end
+                                        right_end - left.offset()
+                                    } else {
+                                        // right is contained inside left
+                                        left.len()
+                                    },
+                                );
+                                if source
+                                    .read_span(
+                                        new_span.inner(),
+                                        self.context_lines,
+                                        self.context_lines,
+                                    )
+                                    .is_ok()
+                                {
+                                    Ok((
+                                        new_span, // We'll throw this away later
+                                        left_conts,
+                                    ))
+                                } else {
+                                    Err(((left, left_conts), (right, right_conts)))
+                                }
+                            } else {
+                                Err(((left, left_conts), (right, right_conts)))
+                            }
                         },
                     );
-                    if source
-                        .read_span(new_span.inner(), self.context_lines, self.context_lines)
-                        .is_ok()
-                    {
-                        Ok((
-                            new_span, // We'll throw this away later
-                            left_conts,
-                        ))
-                    } else {
-                        Err(((left, left_conts), (right, right_conts)))
+                    for (ctx, _) in contexts {
+                        self.render_context(f, source, &ctx, &labels[..])?;
                     }
-                } else {
-                    Err(((left, left_conts), (right, right_conts)))
                 }
-            },
-        );
-        for (ctx, _) in contexts {
-            self.render_context(f, source, &ctx, &labels[..])?;
+            }
         }
         Ok(())
     }

src/protocol.rs

@@ -54,6 +54,11 @@ pub trait Diagnostic: std::error::Error {
     fn labels(&self) -> Option<Box<dyn Iterator<Item = LabeledSpan> + '_>> {
         None
     }
+
+    /// Additional related Diagnostics.
+    fn related<'a>(&'a self) -> Option<Box<dyn Iterator<Item = &'a dyn Diagnostic> + 'a>> {
+        None
+    }
 }
 
 impl std::error::Error for Box<dyn Diagnostic> {