[PATCH 1/3] rust: macros: `parse_generics` add `decl_generics`

[Benno Lossin <benno.lossin@proton.me>]

When parsing generics of a type definition, default values can be
specified. This syntax is however only available on type definitions and
not e.g. impl blocks.

This patch adds the `decl_generics` which can only be used on type
defintions, since they contain the default values for generic
parameters. This patch also changes how `impl_generics` are made up, as
these should be used with `impl<$impl_generics>`, they will omit the
default values.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
---
 rust/macros/helpers.rs  | 91 +++++++++++++++++++++++++++--------------
 rust/macros/pin_data.rs |  1 +
 rust/macros/zeroable.rs |  1 +
 3 files changed, 63 insertions(+), 30 deletions(-)

diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
index afb0f2e3a36a..36fecdd998d0 100644
--- a/rust/macros/helpers.rs
+++ b/rust/macros/helpers.rs
@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 
-use proc_macro::{token_stream, Group, Punct, Spacing, TokenStream, TokenTree};
+use proc_macro::{token_stream, Group, TokenStream, TokenTree};
 
 pub(crate) fn try_ident(it: &mut token_stream::IntoIter) -> Option<String> {
     if let Some(TokenTree::Ident(ident)) = it.next() {
@@ -72,6 +72,7 @@ pub(crate) fn expect_end(it: &mut token_stream::IntoIter) {
 
 pub(crate) struct Generics {
     pub(crate) impl_generics: Vec<TokenTree>,
+    pub(crate) decl_generics: Vec<TokenTree>,
     pub(crate) ty_generics: Vec<TokenTree>,
 }
 
@@ -81,6 +82,8 @@ pub(crate) struct Generics {
 pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
     // `impl_generics`, the declared generics with their bounds.
     let mut impl_generics = vec![];
+    // The generics with bounds and default values.
+    let mut decl_generics = vec![];
     // Only the names of the generics, without any bounds.
     let mut ty_generics = vec![];
     // Tokens not related to the generics e.g. the `where` token and definition.
@@ -90,10 +93,17 @@ pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
     let mut toks = input.into_iter();
     // If we are at the beginning of a generic parameter.
     let mut at_start = true;
-    for tt in &mut toks {
+    let mut skip_until_comma = false;
+    while let Some(tt) = toks.next() {
+        if nesting == 1 && matches!(&tt, TokenTree::Punct(p) if p.as_char() == '>') {
+            // Found the end of the generics.
+            break;
+        } else if nesting >= 1 {
+            decl_generics.push(tt.clone());
+        }
         match tt.clone() {
             TokenTree::Punct(p) if p.as_char() == '<' => {
-                if nesting >= 1 {
+                if nesting >= 1 && !skip_until_comma {
                     // This is inside of the generics and part of some bound.
                     impl_generics.push(tt);
                 }
@@ -105,49 +115,70 @@ pub(crate) fn parse_generics(input: TokenStream) -> (Generics, Vec<TokenTree>) {
                     break;
                 } else {
                     nesting -= 1;
-                    if nesting >= 1 {
+                    if nesting >= 1 && !skip_until_comma {
                         // We are still inside of the generics and part of some bound.
                         impl_generics.push(tt);
                     }
-                    if nesting == 0 {
-                        break;
-                    }
                 }
             }
-            tt => {
+            TokenTree::Punct(p) if skip_until_comma && p.as_char() == ',' => {
                 if nesting == 1 {
-                    // Here depending on the token, it might be a generic variable name.
-                    match &tt {
-                        // Ignore const.
-                        TokenTree::Ident(i) if i.to_string() == "const" => {}
-                        TokenTree::Ident(_) if at_start => {
-                            ty_generics.push(tt.clone());
-                            // We also already push the `,` token, this makes it easier to append
-                            // generics.
-                            ty_generics.push(TokenTree::Punct(Punct::new(',', Spacing::Alone)));
-                            at_start = false;
-                        }
-                        TokenTree::Punct(p) if p.as_char() == ',' => at_start = true,
-                        // Lifetimes begin with `'`.
-                        TokenTree::Punct(p) if p.as_char() == '\'' && at_start => {
-                            ty_generics.push(tt.clone());
-                        }
-                        _ => {}
-                    }
+                    impl_generics.push(TokenTree::Punct(p.clone()));
+                    ty_generics.push(TokenTree::Punct(p));
+                    skip_until_comma = false;
                 }
-                if nesting >= 1 {
-                    impl_generics.push(tt);
-                } else if nesting == 0 {
+            }
+            tt if !skip_until_comma => {
+                match nesting {
                     // If we haven't entered the generics yet, we still want to keep these tokens.
-                    rest.push(tt);
+                    0 => rest.push(tt),
+                    1 => {
+                        // Here depending on the token, it might be a generic variable name.
+                        match tt {
+                            TokenTree::Ident(i) if at_start && i.to_string() == "const" => {
+                                let Some(name) = toks.next() else {
+                                    // Parsing error.
+                                    break;
+                                };
+                                impl_generics.push(TokenTree::Ident(i));
+                                impl_generics.push(name.clone());
+                                ty_generics.push(name.clone());
+                                decl_generics.push(name);
+                                at_start = false;
+                            }
+                            tt @ TokenTree::Ident(_) if at_start => {
+                                impl_generics.push(tt.clone());
+                                ty_generics.push(tt);
+                                at_start = false;
+                            }
+                            TokenTree::Punct(p) if p.as_char() == ',' => {
+                                impl_generics.push(TokenTree::Punct(p.clone()));
+                                ty_generics.push(TokenTree::Punct(p));
+                                at_start = true;
+                            }
+                            // Lifetimes begin with `'`.
+                            TokenTree::Punct(p) if p.as_char() == '\'' && at_start => {
+                                ty_generics.push(TokenTree::Punct(p.clone()));
+                                impl_generics.push(TokenTree::Punct(p));
+                            }
+                            // Generics can have default values, we skip these.
+                            TokenTree::Punct(p) if p.as_char() == '=' => {
+                                skip_until_comma = true;
+                            }
+                            tt => impl_generics.push(tt),
+                        }
+                    }
+                    _ => impl_generics.push(tt),
                 }
             }
+            _ => {}
         }
     }
     rest.extend(toks);
     (
         Generics {
             impl_generics,
+            decl_generics,
             ty_generics,
         },
         rest,
diff --git a/rust/macros/pin_data.rs b/rust/macros/pin_data.rs
index 6d58cfda9872..022e68e9720d 100644
--- a/rust/macros/pin_data.rs
+++ b/rust/macros/pin_data.rs
@@ -10,6 +10,7 @@ pub(crate) fn pin_data(args: TokenStream, input: TokenStream) -> TokenStream {
     let (
         Generics {
             impl_generics,
+            decl_generics: _,
             ty_generics,
         },
         rest,
diff --git a/rust/macros/zeroable.rs b/rust/macros/zeroable.rs
index 0d605c46ab3b..cfee2cec18d5 100644
--- a/rust/macros/zeroable.rs
+++ b/rust/macros/zeroable.rs
@@ -7,6 +7,7 @@ pub(crate) fn derive(input: TokenStream) -> TokenStream {
     let (
         Generics {
             impl_generics,
+            decl_generics: _,
             ty_generics,
         },
         mut rest,

base-commit: 98b1cc82c4affc16f5598d4fa14b1858671b2263
-- 
2.40.1