add `explain` subcommand and explanations to all lints

1 files changed, 177 insertions, 0 deletions

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
+        }
+    }
+}