Auto merge of #117731 - nnethercote:rustc_macros, r=Nilstrieb

`rustc_macros` cleanups

Just some improvements I found while reading over this code.

r? `@Nilstrieb`

9 files changed, 60 insertions, 93 deletions

diff --git a/compiler/rustc_macros/src/current_version.rs b/compiler/rustc_macros/src/current_version.rs
index 5e3b91c17bf..42ca60a6d8a 100644
--- a/compiler/rustc_macros/src/current_version.rs
+++ b/compiler/rustc_macros/src/current_version.rs
@@ -1,37 +1,16 @@
 use proc_macro::TokenStream;
 use proc_macro2::Span;
 use quote::quote;
-use syn::parse::{Parse, ParseStream};
-use syn::{parenthesized, parse_macro_input, LitStr, Token};
 
-pub struct Input {
-    variable: LitStr,
-}
-
-mod kw {
-    syn::custom_keyword!(env);
-}
-
-impl Parse for Input {
-    // Input syntax is `env!("CFG_RELEASE")` to facilitate grepping.
-    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
-        let paren;
-        input.parse::<kw::env>()?;
-        input.parse::<Token![!]>()?;
-        parenthesized!(paren in input);
-        let variable: LitStr = paren.parse()?;
-        Ok(Input { variable })
-    }
-}
-
-pub(crate) fn current_version(input: TokenStream) -> TokenStream {
-    let input = parse_macro_input!(input as Input);
-
-    TokenStream::from(match RustcVersion::parse_env_var(&input.variable) {
+pub(crate) fn current_version(_input: TokenStream) -> TokenStream {
+    let env_var = "CFG_RELEASE";
+    TokenStream::from(match RustcVersion::parse_cfg_release(env_var) {
         Ok(RustcVersion { major, minor, patch }) => quote!(
+            // The produced literal has type `rustc_session::RustcVersion`.
             Self { major: #major, minor: #minor, patch: #patch }
         ),
-        Err(err) => syn::Error::new(Span::call_site(), err).into_compile_error(),
+        Err(err) => syn::Error::new(Span::call_site(), format!("{env_var} env var: {err}"))
+            .into_compile_error(),
     })
 }
 
@@ -42,8 +21,8 @@ struct RustcVersion {
 }
 
 impl RustcVersion {
-    fn parse_env_var(env_var: &LitStr) -> Result<Self, Box<dyn std::error::Error>> {
-        let value = proc_macro::tracked_env::var(env_var.value())?;
+    fn parse_cfg_release(env_var: &str) -> Result<Self, Box<dyn std::error::Error>> {
+        let value = proc_macro::tracked_env::var(env_var)?;
         Self::parse_str(&value)
             .ok_or_else(|| format!("failed to parse rustc version: {:?}", value).into())
     }
diff --git a/compiler/rustc_macros/src/diagnostics/diagnostic.rs b/compiler/rustc_macros/src/diagnostics/diagnostic.rs
index 1a8174bfd96..31ad9cdb216 100644
--- a/compiler/rustc_macros/src/diagnostics/diagnostic.rs
+++ b/compiler/rustc_macros/src/diagnostics/diagnostic.rs
@@ -229,8 +229,8 @@ fn generate_test(slug: &syn::Path, structure: &Structure<'_>) -> TokenStream {
         }
     }
     use std::sync::atomic::{AtomicUsize, Ordering};
-    // We need to make sure that the same diagnostic slug can be used multiple times without causing an
-    // error, so just have a global counter here.
+    // We need to make sure that the same diagnostic slug can be used multiple times without
+    // causing an error, so just have a global counter here.
     static COUNTER: AtomicUsize = AtomicUsize::new(0);
     let slug = slug.get_ident().unwrap();
     let ident = quote::format_ident!("verify_{slug}_{}", COUNTER.fetch_add(1, Ordering::Relaxed));
diff --git a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
index e9a5cd9de97..2755a161d91 100644
--- a/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
+++ b/compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
@@ -53,6 +53,7 @@ pub(crate) struct DiagnosticDeriveVariantBuilder<'parent> {
     /// Slug is a mandatory part of the struct attribute as corresponds to the Fluent message that
     /// has the actual diagnostic message.
     pub slug: SpannedOption<Path>,
+
     /// Error codes are a optional part of the struct attribute - this is only set to detect
     /// multiple specifications.
     pub code: SpannedOption<()>,
@@ -68,7 +69,7 @@ impl DiagnosticDeriveBuilder {
     /// Call `f` for the struct or for each variant of the enum, returning a `TokenStream` with the
     /// tokens from `f` wrapped in an `match` expression. Emits errors for use of derive on unions
     /// or attributes on the type itself when input is an enum.
-    pub fn each_variant<'s, F>(&mut self, structure: &mut Structure<'s>, f: F) -> TokenStream
+    pub(crate) fn each_variant<'s, F>(&mut self, structure: &mut Structure<'s>, f: F) -> TokenStream
     where
         F: for<'a, 'v> Fn(DiagnosticDeriveVariantBuilder<'a>, &VariantInfo<'v>) -> TokenStream,
     {
@@ -121,7 +122,7 @@ impl DiagnosticDeriveBuilder {
 impl<'a> DiagnosticDeriveVariantBuilder<'a> {
     /// Generates calls to `code` and similar functions based on the attributes on the type or
     /// variant.
-    pub fn preamble(&mut self, variant: &VariantInfo<'_>) -> TokenStream {
+    pub(crate) fn preamble(&mut self, variant: &VariantInfo<'_>) -> TokenStream {
         let ast = variant.ast();
         let attrs = &ast.attrs;
         let preamble = attrs.iter().map(|attr| {
@@ -135,7 +136,7 @@ impl<'a> DiagnosticDeriveVariantBuilder<'a> {
 
     /// Generates calls to `span_label` and similar functions based on the attributes on fields or
     /// calls to `set_arg` when no attributes are present.
-    pub fn body(&mut self, variant: &VariantInfo<'_>) -> TokenStream {
+    pub(crate) fn body(&mut self, variant: &VariantInfo<'_>) -> TokenStream {
         let mut body = quote! {};
         // Generate `set_arg` calls first..
         for binding in variant.bindings().iter().filter(|bi| should_generate_set_arg(bi.ast())) {
diff --git a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
index 877271ff077..0f9e68cdc50 100644
--- a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
+++ b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
@@ -478,7 +478,7 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
         }
     }
 
-    pub fn into_tokens(&mut self) -> Result<TokenStream, DiagnosticDeriveError> {
+    pub(crate) fn into_tokens(&mut self) -> Result<TokenStream, DiagnosticDeriveError> {
         let kind_slugs = self.identify_kind()?;
         if kind_slugs.is_empty() {
             if self.is_enum {
diff --git a/compiler/rustc_macros/src/diagnostics/utils.rs b/compiler/rustc_macros/src/diagnostics/utils.rs
index 12563292181..2700f02e33a 100644
--- a/compiler/rustc_macros/src/diagnostics/utils.rs
+++ b/compiler/rustc_macros/src/diagnostics/utils.rs
@@ -17,7 +17,7 @@ use synstructure::{BindingInfo, VariantInfo};
 use super::error::invalid_attr;
 
 thread_local! {
-    pub static CODE_IDENT_COUNT: RefCell<u32> = RefCell::new(0);
+    pub(crate) static CODE_IDENT_COUNT: RefCell<u32> = RefCell::new(0);
 }
 
 /// Returns an ident of the form `__code_N` where `N` is incremented once with every call.
@@ -208,7 +208,7 @@ impl<'ty> FieldInnerTy<'ty> {
         }
     }
 
-    pub fn span(&self) -> proc_macro2::Span {
+    pub(crate) fn span(&self) -> proc_macro2::Span {
         match self {
             FieldInnerTy::Option(ty) | FieldInnerTy::Vec(ty) | FieldInnerTy::Plain(ty) => ty.span(),
         }
@@ -537,7 +537,7 @@ impl fmt::Display for SuggestionKind {
 }
 
 impl SuggestionKind {
-    pub fn to_suggestion_style(&self) -> TokenStream {
+    pub(crate) fn to_suggestion_style(&self) -> TokenStream {
         match self {
             SuggestionKind::Normal => {
                 quote! { rustc_errors::SuggestionStyle::ShowCode }
diff --git a/compiler/rustc_macros/src/hash_stable.rs b/compiler/rustc_macros/src/hash_stable.rs
index 75a2f7009c2..6d23b9ac99d 100644
--- a/compiler/rustc_macros/src/hash_stable.rs
+++ b/compiler/rustc_macros/src/hash_stable.rs
@@ -38,33 +38,16 @@ fn parse_attributes(field: &syn::Field) -> Attributes {
     attrs
 }
 
-pub fn hash_stable_generic_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+pub(crate) fn hash_stable_generic_derive(
+    mut s: synstructure::Structure<'_>,
+) -> proc_macro2::TokenStream {
     let generic: syn::GenericParam = parse_quote!(__CTX);
     s.add_bounds(synstructure::AddBounds::Generics);
     s.add_impl_generic(generic);
     s.add_where_predicate(parse_quote! { __CTX: crate::HashStableContext });
-    let body = s.each(|bi| {
-        let attrs = parse_attributes(bi.ast());
-        if attrs.ignore {
-            quote! {}
-        } else if let Some(project) = attrs.project {
-            quote! {
-                (&#bi.#project).hash_stable(__hcx, __hasher);
-            }
-        } else {
-            quote! {
-                #bi.hash_stable(__hcx, __hasher);
-            }
-        }
-    });
 
-    let discriminant = match s.ast().data {
-        syn::Data::Enum(_) => quote! {
-            ::std::mem::discriminant(self).hash_stable(__hcx, __hasher);
-        },
-        syn::Data::Struct(_) => quote! {},
-        syn::Data::Union(_) => panic!("cannot derive on union"),
-    };
+    let discriminant = hash_stable_discriminant(&mut s);
+    let body = hash_stable_body(&mut s);
 
     s.bound_impl(
         quote!(::rustc_data_structures::stable_hasher::HashStable<__CTX>),
@@ -81,32 +64,13 @@ pub fn hash_stable_generic_derive(mut s: synstructure::Structure<'_>) -> proc_ma
     )
 }
 
-pub fn hash_stable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+pub(crate) fn hash_stable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
     let generic: syn::GenericParam = parse_quote!('__ctx);
     s.add_bounds(synstructure::AddBounds::Generics);
     s.add_impl_generic(generic);
-    let body = s.each(|bi| {
-        let attrs = parse_attributes(bi.ast());
-        if attrs.ignore {
-            quote! {}
-        } else if let Some(project) = attrs.project {
-            quote! {
-                (&#bi.#project).hash_stable(__hcx, __hasher);
-            }
-        } else {
-            quote! {
-                #bi.hash_stable(__hcx, __hasher);
-            }
-        }
-    });
 
-    let discriminant = match s.ast().data {
-        syn::Data::Enum(_) => quote! {
-            ::std::mem::discriminant(self).hash_stable(__hcx, __hasher);
-        },
-        syn::Data::Struct(_) => quote! {},
-        syn::Data::Union(_) => panic!("cannot derive on union"),
-    };
+    let discriminant = hash_stable_discriminant(&mut s);
+    let body = hash_stable_body(&mut s);
 
     s.bound_impl(
         quote!(
@@ -126,3 +90,30 @@ pub fn hash_stable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::To
         },
     )
 }
+
+fn hash_stable_discriminant(s: &mut synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    match s.ast().data {
+        syn::Data::Enum(_) => quote! {
+            ::std::mem::discriminant(self).hash_stable(__hcx, __hasher);
+        },
+        syn::Data::Struct(_) => quote! {},
+        syn::Data::Union(_) => panic!("cannot derive on union"),
+    }
+}
+
+fn hash_stable_body(s: &mut synstructure::Structure<'_>) -> proc_macro2::TokenStream {
+    s.each(|bi| {
+        let attrs = parse_attributes(bi.ast());
+        if attrs.ignore {
+            quote! {}
+        } else if let Some(project) = attrs.project {
+            quote! {
+                (&#bi.#project).hash_stable(__hcx, __hasher);
+            }
+        } else {
+            quote! {
+                #bi.hash_stable(__hcx, __hasher);
+            }
+        }
+    })
+}
diff --git a/compiler/rustc_macros/src/lib.rs b/compiler/rustc_macros/src/lib.rs
index 193dbd75fbd..a6666636032 100644
--- a/compiler/rustc_macros/src/lib.rs
+++ b/compiler/rustc_macros/src/lib.rs
@@ -26,6 +26,9 @@ mod symbols;
 mod type_foldable;
 mod type_visitable;
 
+// Reads the rust version (e.g. "1.75.0") from the CFG_RELEASE env var and
+// produces a `RustcVersion` literal containing that version (e.g.
+// `RustcVersion { major: 1, minor: 75, patch: 0 }`).
 #[proc_macro]
 pub fn current_rustc_version(input: TokenStream) -> TokenStream {
     current_version::current_version(input)
diff --git a/compiler/rustc_macros/src/symbols.rs b/compiler/rustc_macros/src/symbols.rs
index 4129712a6b2..3de4a904e5f 100644
--- a/compiler/rustc_macros/src/symbols.rs
+++ b/compiler/rustc_macros/src/symbols.rs
@@ -19,7 +19,9 @@
 //! ```bash
 //! cargo install cargo-expand          # this is necessary only once
 //! cd compiler/rustc_span
-//! cargo expand > /tmp/rustc_span.rs   # it's a big file
+//! # The specific version number in CFG_RELEASE doesn't matter.
+//! # The output is large.
+//! CFG_RELEASE="0.0.0" cargo +nightly expand > /tmp/rustc_span.rs
 //! ```
 
 use proc_macro2::{Span, TokenStream};
@@ -318,13 +320,4 @@ fn symbols_with_errors(input: TokenStream) -> (TokenStream, Vec<syn::Error>) {
     };
 
     (output, errors.list)
-
-    // To see the generated code, use the "cargo expand" command.
-    // Do this once to install:
-    //      cargo install cargo-expand
-    //
-    // Then, cd to rustc_span and run:
-    //      cargo expand > /tmp/rustc_span_expanded.rs
-    //
-    // and read that file.
 }
diff --git a/compiler/rustc_session/src/version.rs b/compiler/rustc_session/src/version.rs
index 1ad8620bfba..c0c088bcef7 100644
--- a/compiler/rustc_session/src/version.rs
+++ b/compiler/rustc_session/src/version.rs
@@ -9,7 +9,7 @@ pub struct RustcVersion {
 }
 
 impl RustcVersion {
-    pub const CURRENT: Self = current_rustc_version!(env!("CFG_RELEASE"));
+    pub const CURRENT: Self = current_rustc_version!();
 }
 
 impl Display for RustcVersion {