From 7a3c3822ba4a368b0475bc5de89ced78fa8b3cb5 Mon Sep 17 00:00:00 2001
From: Akshay <nerdy@peppe.rs>
Date: Mon, 13 Sep 2021 22:19:18 +0530
Subject: add proc-macro to define lint

---
 macros/Cargo.toml |   9 ++++
 macros/src/lib.rs | 134 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 138 insertions(+), 5 deletions(-)

diff --git a/macros/Cargo.toml b/macros/Cargo.toml
index 6a47e03..b2027fc 100644
--- a/macros/Cargo.toml
+++ b/macros/Cargo.toml
@@ -6,3 +6,12 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+quote = "1.0"
+proc-macro2 = "1.0.27"
+
+[dependencies.syn]
+version = "1.0"
+features = [ "full" ]
+
+[lib]
+proc-macro = true
diff --git a/macros/src/lib.rs b/macros/src/lib.rs
index 31e1bb2..a420d56 100644
--- a/macros/src/lib.rs
+++ b/macros/src/lib.rs
@@ -1,7 +1,131 @@
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
+use std::collections::HashMap;
+
+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,
+    Ident, ItemStruct, Lit, Path, Token,
+};
+
+struct KeyValue {
+    key: Ident,
+    _eq: Token![=],
+    value: Lit,
+}
+
+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, Lit>);
+
+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(),
+        ))
+    }
+}
+
+fn generate_self_impl(struct_name: &Ident) -> TokenStream2 {
+    quote! {
+        impl #struct_name {
+            pub fn new() -> Box<Self> {
+                Box::new(Self)
+            }
+        }
+    }
+}
+
+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 match_with_fn = generate_match_with_fn(meta);
+    quote! {
+        impl Metadata for #struct_name {
+            #name_fn
+            #note_fn
+            #match_with_fn
+        }
     }
 }
+
+fn generate_name_fn(meta: &LintMeta) -> TokenStream2 {
+    let name = meta
+        .0
+        .get(&format_ident!("name"))
+        .unwrap_or_else(|| panic!("`name` not present"));
+    quote! {
+        fn name(&self) -> &str {
+            #name
+        }
+    }
+}
+
+fn generate_note_fn(meta: &LintMeta) -> TokenStream2 {
+    let note = meta
+        .0
+        .get(&format_ident!("note"))
+        .unwrap_or_else(|| panic!("`note` not present"));
+    quote! {
+        fn note(&self) -> &str {
+            #note
+        }
+    }
+}
+
+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 Lit::Str(match_with) = match_with_lit {
+        let path: Path = match_with
+            .parse()
+            .ok()
+            .unwrap_or_else(|| panic!("`match_with` does not contain valid path"));
+        quote! {
+            fn match_with(&self, with: &SyntaxKind) -> bool {
+                *with == #path
+            }
+        }
+    } else {
+        panic!("`match_with` has non-literal 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 struct_name = &struct_item.ident;
+    let self_impl = generate_self_impl(struct_name);
+    let meta_impl = generate_meta_impl(struct_name, &meta);
+    (quote! {
+        #struct_item
+
+        ::lazy_static::lazy_static! {
+            pub static ref LINT: Box<dyn crate::Lint> = #struct_name::new();
+        }
+
+        #self_impl
+        #meta_impl
+
+        impl Lint for #struct_name {}
+    })
+    .into()
+}
-- 
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