Convert define_rule_mapping! to a procedural macro

define_rule_mapping! was previously implemented as a declarative macro,
which was however partially relying on an origin_by_code! proc macro
because declarative macros cannot match on substrings of identifiers.

Currently all define_rule_mapping! lines look like the following:

    TID251 => violations::BannedApi,
    TID252 => violations::BannedRelativeImport,

We want to break up violations.rs, moving the violation definitions to
the respective rule modules. To do this we want to change the previous
lines to:

    TID251 => rules::flake8_tidy_imports::banned_api::BannedApi,
    TID252 => rules::flake8_tidy_imports::relative_imports::RelativeImport,

This however doesn't work because the define_rule_mapping! macro is
currently defined as:

    ($($code:ident => $mod:ident::$name:ident,)+) => { ... }

That is it only supported $module::$name but not longer paths with
multiple modules. While we could define `=> $path:path`[1] then we
could no longer access the last path segment, which we need because
we use it for the DiagnosticKind variant names. And
`$path:path::$last:ident` doesn't work either because it would be
ambiguous (Rust wouldn't know where the path ends ... so path fragments
have to be followed by some punctuation/keyword that may not be part of
paths). And we also cannot just introduce a procedural macro like
path_basename!(...) because the following is not valid Rust code:

    enum Foo { foo!(...), }

(macros cannot be called in the place where you define variants.)

So we have to convert define_rule_mapping! into a proc macro in order to
support paths of arbitrary length and this commit implements that.

[1]: https://doc.rust-lang.org/reference/macros-by-example.html#metavariables

ruff_macros/src/define_rule_mapping.rs

@@ -0,0 +1,133 @@
+use proc_macro2::Span;
+use quote::quote;
+use syn::parse::Parse;
+use syn::{Ident, Path, Token};
+
+pub fn define_rule_mapping(mapping: Mapping) -> proc_macro2::TokenStream {
+    let mut rulecode_variants = quote!();
+    let mut diagkind_variants = quote!();
+    let mut rulecode_kind_match_arms = quote!();
+    let mut rulecode_origin_match_arms = quote!();
+    let mut diagkind_code_match_arms = quote!();
+    let mut diagkind_body_match_arms = quote!();
+    let mut diagkind_fixable_match_arms = quote!();
+    let mut diagkind_commit_match_arms = quote!();
+    let mut from_impls_for_diagkind = quote!();
+
+    for (code, path, name) in mapping.entries {
+        rulecode_variants.extend(quote! {#code,});
+        diagkind_variants.extend(quote! {#name(#path),});
+        rulecode_kind_match_arms.extend(
+            quote! {RuleCode::#code => DiagnosticKind::#name(<#path as Violation>::placeholder()),},
+        );
+        let origin = get_origin(&code);
+        rulecode_origin_match_arms.extend(quote! {RuleCode::#code => RuleOrigin::#origin,});
+        diagkind_code_match_arms.extend(quote! {DiagnosticKind::#name(..) => &RuleCode::#code, });
+        diagkind_body_match_arms
+            .extend(quote! {DiagnosticKind::#name(x) => Violation::message(x), });
+        diagkind_fixable_match_arms
+            .extend(quote! {DiagnosticKind::#name(x) => x.autofix_title_formatter().is_some(),});
+        diagkind_commit_match_arms.extend(
+            quote! {DiagnosticKind::#name(x) => x.autofix_title_formatter().map(|f| f(x)), },
+        );
+        from_impls_for_diagkind.extend(quote! {
+            impl From<#path> for DiagnosticKind {
+                fn from(x: #path) -> Self {
+                    DiagnosticKind::#name(x)
+                }
+            }
+        });
+    }
+
+    quote! {
+        #[derive(
+            AsRefStr,
+            RuleCodePrefix,
+            EnumIter,
+            EnumString,
+            Debug,
+            Display,
+            PartialEq,
+            Eq,
+            Clone,
+            Serialize,
+            Deserialize,
+            Hash,
+            PartialOrd,
+            Ord,
+        )]
+        pub enum RuleCode { #rulecode_variants }
+
+        #[derive(AsRefStr, Debug, PartialEq, Eq, Serialize, Deserialize)]
+        pub enum DiagnosticKind { #diagkind_variants }
+
+
+        impl RuleCode {
+            /// A placeholder representation of the `DiagnosticKind` for the diagnostic.
+            pub fn kind(&self) -> DiagnosticKind {
+                match self { #rulecode_kind_match_arms }
+            }
+
+            pub fn origin(&self) -> RuleOrigin {
+                match self { #rulecode_origin_match_arms }
+            }
+        }
+
+
+        impl DiagnosticKind {
+            /// A four-letter shorthand code for the diagnostic.
+            pub fn code(&self) -> &'static RuleCode {
+                match self { #diagkind_code_match_arms }
+            }
+
+            /// The body text for the diagnostic.
+            pub fn body(&self) -> String {
+                match self { #diagkind_body_match_arms }
+            }
+
+            /// Whether the diagnostic is (potentially) fixable.
+            pub fn fixable(&self) -> bool {
+                match self { #diagkind_fixable_match_arms }
+            }
+
+            /// The message used to describe the fix action for a given `DiagnosticKind`.
+            pub fn commit(&self) -> Option<String> {
+                match self { #diagkind_commit_match_arms }
+            }
+        }
+
+        #from_impls_for_diagkind
+    }
+}
+
+fn get_origin(ident: &Ident) -> Ident {
+    let ident = ident.to_string();
+    let mut iter = crate::prefixes::PREFIX_TO_ORIGIN.iter();
+    let origin = loop {
+        let (prefix, origin) = iter
+            .next()
+            .unwrap_or_else(|| panic!("code doesn't start with any recognized prefix: {ident}"));
+        if ident.starts_with(prefix) {
+            break origin;
+        }
+    };
+    Ident::new(origin, Span::call_site())
+}
+pub struct Mapping {
+    entries: Vec<(Ident, Path, Ident)>,
+}
+
+impl Parse for Mapping {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        let mut entries = Vec::new();
+        while !input.is_empty() {
+            let code: Ident = input.parse()?;
+            let _: Token![=>] = input.parse()?;
+            let path: Path = input.parse()?;
+            let name = path.segments.last().unwrap().ident.clone();
+            let _: Token![,] = input.parse()?;
+            entries.push((code, path, name));
+        }
+        Ok(Mapping { entries })
+    }
+}

ruff_macros/src/lib.rs

@@ -13,11 +13,10 @@
 )]
 #![forbid(unsafe_code)]
 
-use proc_macro2::Span;
-use quote::quote;
-use syn::{parse_macro_input, DeriveInput, Ident};
+use syn::{parse_macro_input, DeriveInput};
 
 mod config;
+mod define_rule_mapping;
 mod prefixes;
 mod rule_code_prefix;
 
@@ -40,21 +39,7 @@ pub fn derive_rule_code_prefix(input: proc_macro::TokenStream) -> proc_macro::To
 }
 
 #[proc_macro]
-pub fn origin_by_code(item: proc_macro::TokenStream) -> proc_macro::TokenStream {
-    let ident = parse_macro_input!(item as Ident).to_string();
-    let mut iter = prefixes::PREFIX_TO_ORIGIN.iter();
-    let origin = loop {
-        let (prefix, origin) = iter
-            .next()
-            .unwrap_or_else(|| panic!("code doesn't start with any recognized prefix: {ident}"));
-        if ident.starts_with(prefix) {
-            break origin;
-        }
-    };
-    let prefix = Ident::new(origin, Span::call_site());
-
-    quote! {
-        RuleOrigin::#prefix
-    }
-    .into()
+pub fn define_rule_mapping(item: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let mapping = parse_macro_input!(item as define_rule_mapping::Mapping);
+    define_rule_mapping::define_rule_mapping(mapping).into()
 }

src/registry.rs

@@ -15,106 +15,7 @@ use crate::fix::Fix;
 use crate::violation::Violation;
 use crate::violations;
 
-macro_rules! define_rule_mapping {
-    ($($code:ident => $mod:ident::$name:ident,)+) => {
-        #[derive(
-            AsRefStr,
-            RuleCodePrefix,
-            EnumIter,
-            EnumString,
-            Debug,
-            Display,
-            PartialEq,
-            Eq,
-            Clone,
-            Serialize,
-            Deserialize,
-            Hash,
-            PartialOrd,
-            Ord,
-        )]
-        pub enum RuleCode {
-            $(
-                $code,
-            )+
-        }
-
-        #[derive(AsRefStr, Debug, PartialEq, Eq, Serialize, Deserialize)]
-        pub enum DiagnosticKind {
-            $(
-                $name($mod::$name),
-            )+
-        }
-
-        impl RuleCode {
-            /// A placeholder representation of the `DiagnosticKind` for the diagnostic.
-            pub fn kind(&self) -> DiagnosticKind {
-                match self {
-                    $(
-                        RuleCode::$code => DiagnosticKind::$name(<$mod::$name as Violation>::placeholder()),
-                    )+
-                }
-            }
-
-            pub fn origin(&self) -> RuleOrigin {
-                match self {
-                    $(
-                        RuleCode::$code => ruff_macros::origin_by_code!($code),
-                    )+
-                }
-            }
-        }
-
-        impl DiagnosticKind {
-            /// A four-letter shorthand code for the diagnostic.
-            pub fn code(&self) -> &'static RuleCode {
-                match self {
-                    $(
-                        DiagnosticKind::$name(..) => &RuleCode::$code,
-                    )+
-                }
-            }
-
-            /// The body text for the diagnostic.
-            pub fn body(&self) -> String {
-                match self {
-                    $(
-                        DiagnosticKind::$name(x) => Violation::message(x),
-                    )+
-                }
-            }
-
-            /// Whether the diagnostic is (potentially) fixable.
-            pub fn fixable(&self) -> bool {
-                match self {
-                    $(
-                        DiagnosticKind::$name(x) => x.autofix_title_formatter().is_some(),
-                    )+
-                }
-            }
-
-            /// The message used to describe the fix action for a given `DiagnosticKind`.
-            pub fn commit(&self) -> Option<String> {
-                match self {
-                    $(
-                        DiagnosticKind::$name(x) => x.autofix_title_formatter().map(|f| f(x)),
-                    )+
-                }
-            }
-        }
-
-        $(
-            impl From<$mod::$name> for DiagnosticKind {
-                fn from(x: $mod::$name) -> Self {
-                    DiagnosticKind::$name(x)
-                }
-            }
-        )+
-
-    };
-}
-
-define_rule_mapping!(
+ruff_macros::define_rule_mapping!(
     // pycodestyle errors
     E401 => violations::MultipleImportsOnOneLine,
     E402 => violations::ModuleImportNotAtTopOfFile,