add `explain` subcommand and explanations to all lints

3 files changed, 216 insertions, 162 deletions

diff --git a/macros/src/explain.rs b/macros/src/explain.rs
new file mode 100644
index 0000000..41dc5d4
--- /dev/null
+++ b/macros/src/explain.rs
@@ -0,0 +1,28 @@
+use proc_macro2::TokenStream as TokenStream2;
+use quote::quote;
+use syn::{ItemStruct, Lit, Meta, MetaNameValue};
+
+pub fn generate_explain_impl(struct_item: &ItemStruct) -> TokenStream2 {
+    let struct_name = &struct_item.ident;
+    let explain = struct_item
+        .attrs
+        .iter()
+        .filter_map(|attr| match attr.parse_meta().ok() {
+            Some(Meta::NameValue(MetaNameValue {
+                path,
+                lit: Lit::Str(str_lit),
+                ..
+            })) if path.is_ident("doc") => Some(str_lit.value()),
+            _ => None,
+        })
+        .map(|s| s.strip_prefix(' ').unwrap_or(&s).to_owned())
+        .collect::<Vec<_>>()
+        .join("\n");
+    quote! {
+        impl crate::Explain for #struct_name {
+            fn explanation(&self) -> &'static str {
+                #explain
+            }
+        }
+    }
+}
diff --git a/macros/src/lib.rs b/macros/src/lib.rs
index 127b4cb..86fa509 100644
--- a/macros/src/lib.rs
+++ b/macros/src/lib.rs
@@ -1,44 +1,12 @@
-use std::collections::HashMap;
+mod explain;
+mod metadata;
 
+use explain::generate_explain_impl;
+use metadata::{generate_meta_impl, RawLintMeta};
 use proc_macro::TokenStream;
 use proc_macro2::TokenStream as TokenStream2;
-
-use quote::{format_ident, quote};
-use syn::{
-    parse::{Parse, ParseStream, Result as ParseResult},
-    parse_macro_input,
-    punctuated::Punctuated,
-    Expr, Ident, ItemStruct, Lit, Token,
-};
-
-struct KeyValue {
-    key: Ident,
-    _eq: Token![=],
-    value: Expr,
-}
-
-impl Parse for KeyValue {
-    fn parse(input: ParseStream) -> ParseResult<Self> {
-        Ok(Self {
-            key: input.parse()?,
-            _eq: input.parse()?,
-            value: input.parse()?,
-        })
-    }
-}
-
-struct LintMeta(HashMap<Ident, Expr>);
-
-impl Parse for LintMeta {
-    fn parse(input: ParseStream) -> ParseResult<Self> {
-        Ok(Self(
-            Punctuated::<KeyValue, Token![,]>::parse_terminated(input)?
-                .into_iter()
-                .map(|item| (item.key, item.value))
-                .collect(),
-        ))
-    }
-}
+use quote::quote;
+use syn::{parse_macro_input, Ident, ItemStruct};
 
 fn generate_self_impl(struct_name: &Ident) -> TokenStream2 {
     quote! {
@@ -50,136 +18,16 @@ fn generate_self_impl(struct_name: &Ident) -> TokenStream2 {
     }
 }
 
-fn generate_meta_impl(struct_name: &Ident, meta: &LintMeta) -> TokenStream2 {
-    let name_fn = generate_name_fn(meta);
-    let note_fn = generate_note_fn(meta);
-    let code_fn = generate_code_fn(meta);
-    let report_fn = generate_report_fn();
-    let match_with_fn = generate_match_with_fn(meta);
-    let match_kind = generate_match_kind(meta);
-    quote! {
-        impl Metadata for #struct_name {
-            #name_fn
-            #note_fn
-            #code_fn
-            #report_fn
-            #match_with_fn
-            #match_kind
-        }
-    }
-}
-
-fn generate_name_fn(meta: &LintMeta) -> TokenStream2 {
-    let name = meta
-        .0
-        .get(&format_ident!("name"))
-        .unwrap_or_else(|| panic!("`name` not present"));
-    if let syn::Expr::Lit(name_lit) = name {
-        if let Lit::Str(name_str) = &name_lit.lit {
-            return quote! {
-                fn name() -> &'static str {
-                    #name_str
-                }
-            };
-        }
-    }
-    panic!("Invalid value for `name`");
-}
-
-fn generate_note_fn(meta: &LintMeta) -> TokenStream2 {
-    let note = meta
-        .0
-        .get(&format_ident!("note"))
-        .unwrap_or_else(|| panic!("`note` not present"));
-    if let syn::Expr::Lit(note_lit) = note {
-        if let Lit::Str(note_str) = &note_lit.lit {
-            return quote! {
-                fn note() -> &'static str {
-                    #note_str
-                }
-            };
-        }
-    }
-    panic!("Invalid value for `note`");
-}
-
-fn generate_code_fn(meta: &LintMeta) -> TokenStream2 {
-    let code = meta
-        .0
-        .get(&format_ident!("code"))
-        .unwrap_or_else(|| panic!("`code` not present"));
-    if let syn::Expr::Lit(code_lit) = code {
-        if let Lit::Int(code_int) = &code_lit.lit {
-            return quote! {
-                fn code() -> u32 {
-                    #code_int
-                }
-            };
-        }
-    }
-    panic!("Invalid value for `note`");
-}
-
-fn generate_report_fn() -> TokenStream2 {
-    quote! {
-        fn report() -> Report {
-            Report::new(Self::note(), Self::code())
-        }
-    }
-}
-
-fn generate_match_with_fn(meta: &LintMeta) -> TokenStream2 {
-    let match_with_lit = meta
-        .0
-        .get(&format_ident!("match_with"))
-        .unwrap_or_else(|| panic!("`match_with` not present"));
-    if let syn::Expr::Path(match_path) = match_with_lit {
-        quote! {
-            fn match_with(&self, with: &SyntaxKind) -> bool {
-                #match_path == *with
-            }
-        }
-    } else if let syn::Expr::Array(array_expr) = match_with_lit {
-        quote! {
-            fn match_with(&self, with: &SyntaxKind) -> bool {
-                #array_expr.contains(with)
-            }
-        }
-    } else {
-        panic!("`match_with` has non-path value")
-    }
-}
-
-fn generate_match_kind(meta: &LintMeta) -> TokenStream2 {
-    let match_with_lit = meta
-        .0
-        .get(&format_ident!("match_with"))
-        .unwrap_or_else(|| panic!("`match_with` not present"));
-    if let syn::Expr::Path(match_path) = match_with_lit {
-        quote! {
-            fn match_kind(&self) -> Vec<SyntaxKind> {
-                vec![#match_path]
-            }
-        }
-    } else if let syn::Expr::Array(array_expr) = match_with_lit {
-        quote! {
-            fn match_kind(&self) -> Vec<SyntaxKind> {
-                #array_expr.to_vec()
-            }
-        }
-    } else {
-        panic!("`match_with` has non-path value")
-    }
-}
-
 #[proc_macro_attribute]
 pub fn lint(attr: TokenStream, item: TokenStream) -> TokenStream {
     let struct_item = parse_macro_input!(item as ItemStruct);
-    let meta = parse_macro_input!(attr as LintMeta);
+    let meta = parse_macro_input!(attr as RawLintMeta);
 
     let struct_name = &struct_item.ident;
     let self_impl = generate_self_impl(struct_name);
     let meta_impl = generate_meta_impl(struct_name, &meta);
+    let explain_impl = generate_explain_impl(&struct_item);
+
     (quote! {
         #struct_item
 
@@ -189,8 +37,9 @@ pub fn lint(attr: TokenStream, item: TokenStream) -> TokenStream {
 
         #self_impl
         #meta_impl
+        #explain_impl
 
-        impl Lint for #struct_name {}
+        impl crate::Lint for #struct_name {}
     })
     .into()
 }
diff --git a/macros/src/metadata.rs b/macros/src/metadata.rs
new file mode 100644
index 0000000..b41eb9c
--- /dev/null
+++ b/macros/src/metadata.rs
@@ -0,0 +1,177 @@
+use std::collections::HashMap;
+
+use proc_macro2::TokenStream as TokenStream2;
+use quote::{format_ident, quote};
+use syn::{
+    parse::{Parse, ParseStream, Result},
+    punctuated::Punctuated,
+    Expr, ExprArray, Ident, Lit, Path, Token,
+};
+
+struct KeyValue {
+    key: Ident,
+    _eq: Token![=],
+    value: Expr,
+}
+
+impl Parse for KeyValue {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(Self {
+            key: input.parse()?,
+            _eq: input.parse()?,
+            value: input.parse()?,
+        })
+    }
+}
+
+pub struct RawLintMeta(HashMap<Ident, Expr>);
+
+impl Parse for RawLintMeta {
+    fn parse(input: ParseStream) -> Result<Self> {
+        Ok(Self(
+            Punctuated::<KeyValue, Token![,]>::parse_terminated(input)?
+                .into_iter()
+                .map(|item| (item.key, item.value))
+                .collect(),
+        ))
+    }
+}
+
+pub struct LintMeta<'μ> {
+    name: &'μ Lit,
+    note: &'μ Lit,
+    code: &'μ Lit,
+    match_with: MatchWith<'μ>,
+}
+
+enum MatchWith<'π> {
+    Path(&'π Path),
+    Array(&'π ExprArray),
+}
+
+fn extract<'λ>(id: &str, raw: &'λ RawLintMeta) -> &'λ Expr {
+    raw.0
+        .get(&format_ident!("{}", id))
+        .unwrap_or_else(|| panic!("`{}` not present", id))
+}
+
+fn as_lit(e: &Expr) -> &Lit {
+    match e {
+        Expr::Lit(l) => &l.lit,
+        _ => panic!("expected a literal"),
+    }
+}
+
+impl<'μ> LintMeta<'μ> {
+    fn from_raw(raw: &'μ RawLintMeta) -> Self {
+        let name = as_lit(extract("name", raw));
+        let note = as_lit(extract("note", raw));
+        let code = as_lit(extract("code", raw));
+        let match_with_expr = extract("match_with", raw);
+        let match_with = match match_with_expr {
+            Expr::Path(p) => MatchWith::Path(&p.path),
+            Expr::Array(a) => MatchWith::Array(a),
+            _ => panic!("`match_with` is neither a path nor an array"),
+        };
+        Self {
+            name,
+            note,
+            code,
+            match_with,
+        }
+    }
+
+    fn generate_name_fn(&self) -> TokenStream2 {
+        let name_str = self.name;
+        return quote! {
+            fn name(&self) -> &'static str {
+                #name_str
+            }
+        };
+    }
+
+    fn generate_note_fn(&self) -> TokenStream2 {
+        let note_str = self.note;
+        return quote! {
+            fn note(&self) -> &'static str {
+                #note_str
+            }
+        };
+    }
+
+    fn generate_code_fn(&self) -> TokenStream2 {
+        let code_int = self.code;
+        return quote! {
+            fn code(&self) -> u32 {
+                #code_int
+            }
+        };
+    }
+
+    fn generate_match_with_fn(&self) -> TokenStream2 {
+        match self.match_with {
+            MatchWith::Path(p) => {
+                quote! {
+                    fn match_with(&self, with: &SyntaxKind) -> bool {
+                        #p == *with
+                    }
+                }
+            }
+            MatchWith::Array(a) => {
+                quote! {
+                    fn match_with(&self, with: &SyntaxKind) -> bool {
+                        #a.contains(with)
+                    }
+                }
+            }
+        }
+    }
+
+    fn generate_match_kind_fn(&self) -> TokenStream2 {
+        match self.match_with {
+            MatchWith::Path(p) => {
+                quote! {
+                    fn match_kind(&self) -> Vec<SyntaxKind> {
+                        vec![#p]
+                    }
+                }
+            }
+            MatchWith::Array(a) => {
+                quote! {
+                    fn match_kind(&self) -> Vec<SyntaxKind> {
+                        #a.to_vec()
+                    }
+                }
+            }
+        }
+    }
+
+    fn generate_report_fn(&self) -> TokenStream2 {
+        quote! {
+            fn report(&self) -> crate::Report {
+                crate::Report::new(self.note(), self.code())
+            }
+        }
+    }
+}
+
+pub fn generate_meta_impl(struct_name: &Ident, meta: &RawLintMeta) -> TokenStream2 {
+    let not_raw = LintMeta::from_raw(&meta);
+    let name_fn = not_raw.generate_name_fn();
+    let note_fn = not_raw.generate_note_fn();
+    let code_fn = not_raw.generate_code_fn();
+    let match_with_fn = not_raw.generate_match_with_fn();
+    let match_kind = not_raw.generate_match_kind_fn();
+    let report_fn = not_raw.generate_report_fn();
+
+    quote! {
+        impl crate::Metadata for #struct_name {
+            #name_fn
+            #note_fn
+            #code_fn
+            #match_with_fn
+            #match_kind
+            #report_fn
+        }
+    }
+}