From cfe2dafe5e5e585ea5c060a4ceceb606ec688d27 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sosth=C3=A8ne=20Gu=C3=A9don?= <sosthene@nitrokey.com>
Date: Wed, 12 Mar 2025 12:03:27 +0100
Subject: [PATCH] Allow skipping incrementing when using skip

---
 src/parse.rs    | 22 +++++++++++++++++-----
 tests/basics.rs |  3 +++
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/src/parse.rs b/src/parse.rs
index 243b3bc..814031f 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -107,10 +107,13 @@ fn fields_from_ast(
     fields: &syn::punctuated::Punctuated<syn::Field, Token![,]>,
 ) -> Result<Vec<Field>> {
     // serde::internals::ast.rs:L183
+    let mut index = 0;
     fields
         .iter()
-        .enumerate()
-        .map(|(index, field)| {
+        .map(|field| {
+            let current_index = index;
+            index += 1;
+
             let mut skip_serializing_if = Skip::None;
             for attr in &field.attrs {
                 if attr.path().is_ident("serde") {
@@ -125,9 +128,18 @@ fn fields_from_ast(
                             skip_serializing_if = Skip::If(syn::parse2(tokens)?);
                             Ok(())
                         } else if meta.path.is_ident("skip") {
-                            if meta.value().is_ok() {
-                                return Err(meta.error("`skip` does not expect any value"));
+                            if meta.input.peek(syn::token::Paren) {
+                                meta.parse_nested_meta(|skip_meta| {
+                                    if !skip_meta.path.is_ident("no_increment") {
+                                        Err(skip_meta
+                                            .error("`skip` only accepts `no_increment` as value"))
+                                    } else {
+                                        index -= 1;
+                                        Ok(())
+                                    }
+                                })?;
                             }
+
                             if !skip_serializing_if.is_none() {
                                 return Err(meta
                                     .error("Multiple attributes for skip_serializing_if or skip"));
@@ -155,7 +167,7 @@ fn fields_from_ast(
                         return Err(Error::new_spanned(fields, "Tuple struct are not supported"));
                     }
                 },
-                index,
+                index: current_index,
                 // TODO: make this... more concise? handle errors? the thing with the spans?
                 skip_serializing_if,
             })
diff --git a/tests/basics.rs b/tests/basics.rs
index 6909bcf..faa44d1 100644
--- a/tests/basics.rs
+++ b/tests/basics.rs
@@ -59,6 +59,8 @@ mod some_keys {
         pub number: i32,
         #[serde(skip)]
         pub ignored: i32,
+        #[serde(skip(no_increment))]
+        pub ignored2: i32,
         pub bytes: &'a ByteArray<7>,
         pub string: &'b str,
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -111,6 +113,7 @@ mod some_keys {
         let value = SomeRefKeys {
             number: -7,
             ignored: 0,
+            ignored2: 0,
             bytes: &BYTE_ARRAY,
             string: "so serde",
             option: None,