1 files changed, 146 insertions, 0 deletions
diff --git a/src/help.rs b/src/help.rs
new file mode 100644
index 0000000..1c21054
--- /dev/null
+++ b/src/help.rs
@@ -0,0 +1,146 @@
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote};
+use syn::{
+    parenthesized,
+    parse::{Parse, ParseStream},
+    spanned::Spanned,
+    Fields, Token,
+};
+
+use crate::{
+    diagnostic::{DiagnosticConcreteArgs, DiagnosticDef},
+    utils::{display_pat_members, gen_all_variants_with},
+};
+use crate::{
+    fmt::{self, Display},
+    forward::WhichFn,
+};
+
+pub enum Help {
+    Display(Display),
+    Field(syn::Member, Box<syn::Type>),
+}
+
+impl Parse for Help {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let ident = input.parse::<syn::Ident>()?;
+        if ident == "help" {
+            let la = input.lookahead1();
+            if la.peek(syn::token::Paren) {
+                let content;
+                parenthesized!(content in input);
+                let fmt = content.parse()?;
+                let args = if content.is_empty() {
+                    TokenStream::new()
+                } else {
+                    fmt::parse_token_expr(&content, false)?
+                };
+                let display = Display {
+                    fmt,
+                    args,
+                    has_bonus_display: false,
+                };
+                Ok(Help::Display(display))
+            } else {
+                input.parse::<Token![=]>()?;
+                Ok(Help::Display(Display {
+                    fmt: input.parse()?,
+                    args: TokenStream::new(),
+                    has_bonus_display: false,
+                }))
+            }
+        } else {
+            Err(syn::Error::new(ident.span(), "not a help"))
+        }
+    }
+}
+
+impl Help {
+    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("help") {
+                    let help = 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(Help::Field(help, Box::new(field.ty.clone()))));
+                }
+            }
+        }
+        Ok(None)
+    }
+    pub(crate) fn gen_enum(variants: &[DiagnosticDef]) -> Option<TokenStream> {
+        gen_all_variants_with(
+            variants,
+            WhichFn::Help,
+            |ident, fields, DiagnosticConcreteArgs { help, .. }| {
+                let (display_pat, display_members) = display_pat_members(fields);
+                match &help.as_ref()? {
+                    Help::Display(display) => {
+                        let (fmt, args) = display.expand_shorthand_cloned(&display_members);
+                        Some(quote! {
+                            Self::#ident #display_pat => std::option::Option::Some(std::boxed::Box::new(format!(#fmt #args))),
+                        })
+                    }
+                    Help::Field(member, ty) => {
+                        let help = match &member {
+                            syn::Member::Named(ident) => ident.clone(),
+                            syn::Member::Unnamed(syn::Index { index, .. }) => {
+                                format_ident!("_{}", index)
+                            }
+                        };
+                        let var = quote! { __miette_internal_var };
+                        Some(quote! {
+                            Self::#ident #display_pat => {
+                                use miette::macro_helpers::ToOption;
+                                miette::macro_helpers::OptionalWrapper::<#ty>::new().to_option(&#help).as_ref().map(|#var| -> std::boxed::Box<dyn std::fmt::Display + '_> { std::boxed::Box::new(format!("{}", #var)) })
+                            },
+                        })
+                    }
+                }
+            },
+        )
+    }
+
+    pub(crate) fn gen_struct(&self, fields: &Fields) -> Option<TokenStream> {
+        let (display_pat, display_members) = display_pat_members(fields);
+        match self {
+            Help::Display(display) => {
+                let (fmt, args) = display.expand_shorthand_cloned(&display_members);
+                Some(quote! {
+                    fn help(&self) -> std::option::Option<std::boxed::Box<dyn std::fmt::Display + '_>> {
+                        #[allow(unused_variables, deprecated)]
+                        let Self #display_pat = self;
+                        std::option::Option::Some(std::boxed::Box::new(format!(#fmt #args)))
+                    }
+                })
+            }
+            Help::Field(member, ty) => {
+                let var = quote! { __miette_internal_var };
+                Some(quote! {
+                    fn help(&self) -> std::option::Option<std::boxed::Box<dyn std::fmt::Display + '_>> {
+                        #[allow(unused_variables, deprecated)]
+                        let Self #display_pat = self;
+                        use miette::macro_helpers::ToOption;
+                        miette::macro_helpers::OptionalWrapper::<#ty>::new().to_option(&self.#member).as_ref().map(|#var| -> std::boxed::Box<dyn std::fmt::Display + '_> { std::boxed::Box::new(format!("{}", #var)) })
+                    }
+                })
+            }
+        }
+    }
+}