From 78b3aa227f049df2012b622fefcc8322c8113c0d Mon Sep 17 00:00:00 2001
From: Sean Lynch <42618346+swlynch99@users.noreply.github.com>
Date: Mon, 18 Aug 2025 13:00:41 -0700
Subject: [PATCH 1/4] Allow overriding field and struct visibility in
 substructs

Currently substructs and their fields will have their visibility copied
from the base struct. This commit adds the ability to override that.
---
 src/lib.rs                                    | 32 +++++++++++++--
 src/substruct.rs                              | 39 ++++++++++++++++++-
 tests/ui/fail/base-visibility-override.rs     |  6 +++
 tests/ui/fail/base-visibility-override.stderr |  5 +++
 tests/ui/fail/inaccessible-field.rs           | 19 +++++++++
 tests/ui/fail/inaccessible-field.stderr       |  5 +++
 tests/ui/fail/inaccessible-struct.rs          | 14 +++++++
 tests/ui/fail/inaccessible-struct.stderr      | 17 ++++++++
 tests/ui/pass/expression-vis.rs               | 23 +++++++++++
 tests/ui/pass/no-warn-pub-self.rs             | 13 +++++++
 10 files changed, 168 insertions(+), 5 deletions(-)
 create mode 100644 tests/ui/fail/base-visibility-override.rs
 create mode 100644 tests/ui/fail/base-visibility-override.stderr
 create mode 100644 tests/ui/fail/inaccessible-field.rs
 create mode 100644 tests/ui/fail/inaccessible-field.stderr
 create mode 100644 tests/ui/fail/inaccessible-struct.rs
 create mode 100644 tests/ui/fail/inaccessible-struct.stderr
 create mode 100644 tests/ui/pass/expression-vis.rs
 create mode 100644 tests/ui/pass/no-warn-pub-self.rs

diff --git a/src/lib.rs b/src/lib.rs
index 7e1c28a..dee66af 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -105,6 +105,32 @@
 //! }
 //! ```
 //!
+//! # Overriding visibility for emitted structs and fields
+//! Normally, `substruct` will copy the visibility definition over from the
+//! base struct. However, you can override it by adding a visibility specifier
+//! in front of the struct name within the `#[substruct]` attribute.
+//! ```
+//! # use substruct::substruct;
+//! #
+//! // Both A and B are pub, but C is pub(crate).
+//! #[substruct(B, pub(crate) C)]
+//! pub struct A {
+//!     // This field is public in structs A and C, but only pub(crate) in C.
+//!     #[substruct(pub(crate) B, C)]
+//!     pub field1: u32,
+//!
+//!     // Making a field private can be done by using pub(self)
+//!     #[substruct(pub(self) C)]
+//!     pub field2: u32,
+//!
+//!     // You can also override the visibility when using expressions.
+//!     // The overridden visibility applies to all structs specified in the
+//!     // expression.
+//!     #[substruct(pub(crate) any(B, C))]
+//!     pub field3: u32,
+//! }
+//! ```
+//!
 //! # Managing attributes on generated structs
 //! Sometimes you may want attributes to only apply to some of the emitted
 //! structs. To do so, you can use the `#[substruct_attr]` macro to only emit
@@ -166,7 +192,7 @@
 //! }
 //! ```
 //!
-//! > The parent struct as always implicitly included in the set of structs
+//! > The parent struct is always implicitly included in the set of structs
 //! > that each field is emitted for. This means that putting `not(A)` in the
 //! > the struct above would not exclude the field from `A` (and is, in fact,
 //! > equivalent to `all()`).
@@ -190,8 +216,8 @@
 //! }
 //! ```
 //!
-//! If multiple documentation overrides apply to a single field, then the first
-//! one to apply will be used.
+//! If multiple overrides apply to a single field, then the first one to apply
+//! will be used.
 //!
 //! # Generics
 //! Generics are currently _mostly_ supported. You can use generics with
diff --git a/src/substruct.rs b/src/substruct.rs
index 89135cf..6ebebab 100644
--- a/src/substruct.rs
+++ b/src/substruct.rs
@@ -18,6 +18,7 @@ use crate::expr::Expr;
 /// ```
 struct SubstructInputArg {
     docs: Vec<syn::Attribute>,
+    vis: syn::Visibility,
     expr: Expr,
 }
 
@@ -36,6 +37,7 @@ impl Parse for SubstructInputArg {
 
         Ok(Self {
             docs: attrs,
+            vis: input.parse()?,
             expr: input.parse()?,
         })
     }
@@ -78,6 +80,7 @@ impl Parse for SubstructAttrInput {
 
 struct TopLevelArg {
     docs: Vec<syn::Attribute>,
+    vis: syn::Visibility,
 }
 
 struct Emitter<'a> {
@@ -106,7 +109,13 @@ impl<'a> Emitter<'a> {
             .args
             .into_iter()
             .filter_map(|arg| match arg.expr {
-                Expr::Ident(ident) => Some((ident.clone(), TopLevelArg { docs: arg.docs })),
+                Expr::Ident(ident) => Some((
+                    ident.clone(),
+                    TopLevelArg {
+                        docs: arg.docs,
+                        vis: arg.vis,
+                    },
+                )),
                 expr => {
                     errors.push(syn::Error::new_spanned(
                     expr,
@@ -118,7 +127,13 @@ impl<'a> Emitter<'a> {
             .collect();
 
         if !args.contains_key(&input.ident) {
-            args.insert(input.ident.clone(), TopLevelArg { docs: Vec::new() });
+            args.insert(
+                input.ident.clone(),
+                TopLevelArg {
+                    docs: Vec::new(),
+                    vis: syn::Visibility::Inherited,
+                },
+            );
         }
 
         Ok(Self {
@@ -151,6 +166,17 @@ impl<'a> Emitter<'a> {
         let mut input = self.input.clone();
         input.ident = name.clone();
 
+        if !matches!(tla.vis, syn::Visibility::Inherited) {
+            if *name == self.input.ident {
+                self.errors.push(syn::Error::new_spanned(
+                    &tla.vis,
+                    "cannot override the visibility of the base struct",
+                ));
+            }
+
+            input.vis = tla.vis.clone();
+        }
+
         if !tla.docs.is_empty() {
             input.attrs.retain(|attr| !attr.path().is_ident("doc"));
             input.attrs.extend_from_slice(&tla.docs);
@@ -169,6 +195,10 @@ impl<'a> Emitter<'a> {
             syn::Data::Union(data) => self.filter_fields_named(&mut data.fields, name),
         };
 
+        input
+            .attrs
+            .push(syn::parse_quote!(#[allow(clippy::needless_pub_self)]));
+
         input.to_tokens(&mut self.tokens);
 
         if input.ident != self.input.ident {
@@ -333,6 +363,7 @@ impl<'a> Emitter<'a> {
 
         substruct.args.push(SubstructInputArg {
             docs: Vec::new(),
+            vis: syn::Visibility::Inherited,
             expr: Expr::Ident(self.input.ident.clone()),
         });
 
@@ -343,6 +374,10 @@ impl<'a> Emitter<'a> {
 
         self.filter_attrs(&mut field.attrs, name);
 
+        if !matches!(arg.vis, syn::Visibility::Inherited) {
+            field.vis = arg.vis.clone();
+        }
+
         if !arg.docs.is_empty() {
             field.attrs.retain(|attr| !attr.path().is_ident("doc"));
             field.attrs.extend_from_slice(&arg.docs);
diff --git a/tests/ui/fail/base-visibility-override.rs b/tests/ui/fail/base-visibility-override.rs
new file mode 100644
index 0000000..202d154
--- /dev/null
+++ b/tests/ui/fail/base-visibility-override.rs
@@ -0,0 +1,6 @@
+use substruct::substruct;
+
+#[substruct(pub(crate) Test)]
+pub struct Test {}
+
+fn main() {}
diff --git a/tests/ui/fail/base-visibility-override.stderr b/tests/ui/fail/base-visibility-override.stderr
new file mode 100644
index 0000000..aa356b3
--- /dev/null
+++ b/tests/ui/fail/base-visibility-override.stderr
@@ -0,0 +1,5 @@
+error: cannot override the visibility of the base struct
+ --> tests/ui/fail/base-visibility-override.rs:3:13
+  |
+3 | #[substruct(pub(crate) Test)]
+  |             ^^^^^^^^^^
diff --git a/tests/ui/fail/inaccessible-field.rs b/tests/ui/fail/inaccessible-field.rs
new file mode 100644
index 0000000..c11b59a
--- /dev/null
+++ b/tests/ui/fail/inaccessible-field.rs
@@ -0,0 +1,19 @@
+
+mod inner {
+    use substruct::substruct;
+
+    #[substruct(A)]
+    #[derive(Default)]
+    pub struct Test {
+        #[substruct(pub(self) A)]
+        pub field1: u32,
+        pub field2: u32,
+    }
+}
+
+fn main() {
+    use self::inner::*;
+
+    let value = A::default();
+    let _field = value.field1;
+}
diff --git a/tests/ui/fail/inaccessible-field.stderr b/tests/ui/fail/inaccessible-field.stderr
new file mode 100644
index 0000000..4c83cd6
--- /dev/null
+++ b/tests/ui/fail/inaccessible-field.stderr
@@ -0,0 +1,5 @@
+error[E0616]: field `field1` of struct `inner::A` is private
+  --> tests/ui/fail/inaccessible-field.rs:18:24
+   |
+18 |     let _field = value.field1;
+   |                        ^^^^^^ private field
diff --git a/tests/ui/fail/inaccessible-struct.rs b/tests/ui/fail/inaccessible-struct.rs
new file mode 100644
index 0000000..1daf99f
--- /dev/null
+++ b/tests/ui/fail/inaccessible-struct.rs
@@ -0,0 +1,14 @@
+mod inner {
+    use substruct::substruct;
+
+    #[substruct(pub(self) A)]
+    #[derive(Default)]
+    pub struct Test {
+        #[substruct(A)]
+        pub field: u32,
+    }
+}
+
+fn main() {
+    let _ = crate::inner::A::default();
+}
diff --git a/tests/ui/fail/inaccessible-struct.stderr b/tests/ui/fail/inaccessible-struct.stderr
new file mode 100644
index 0000000..0531998
--- /dev/null
+++ b/tests/ui/fail/inaccessible-struct.stderr
@@ -0,0 +1,17 @@
+error[E0603]: struct `A` is private
+  --> tests/ui/fail/inaccessible-struct.rs:13:27
+   |
+13 |     let _ = crate::inner::A::default();
+   |                           ^ private struct
+   |
+note: the struct `A` is defined here
+  --> tests/ui/fail/inaccessible-struct.rs:4:17
+   |
+ 4 |       #[substruct(pub(self) A)]
+   |  _________________^
+ 5 | |     #[derive(Default)]
+ 6 | |     pub struct Test {
+ 7 | |         #[substruct(A)]
+ 8 | |         pub field: u32,
+ 9 | |     }
+   | |_____^
diff --git a/tests/ui/pass/expression-vis.rs b/tests/ui/pass/expression-vis.rs
new file mode 100644
index 0000000..78cdb93
--- /dev/null
+++ b/tests/ui/pass/expression-vis.rs
@@ -0,0 +1,23 @@
+
+
+mod inner {
+    use substruct::substruct;
+
+    #[substruct(A, B)]
+    #[derive(Default)]
+    pub struct Test
+    {
+        #[substruct(pub any(A, B))]
+        field: u32,
+    }
+}
+
+fn main() {
+    use crate::inner::*;
+
+    let a = A::default();
+    let b = B::default();
+
+    let _ = a.field;
+    let _ = b.field;
+}
diff --git a/tests/ui/pass/no-warn-pub-self.rs b/tests/ui/pass/no-warn-pub-self.rs
new file mode 100644
index 0000000..9e9b236
--- /dev/null
+++ b/tests/ui/pass/no-warn-pub-self.rs
@@ -0,0 +1,13 @@
+#![allow(dead_code)]
+#![deny(clippy::needless_pub_self)]
+
+use substruct::substruct;
+
+#[substruct(pub(self) A)]
+pub struct Test {
+    #[substruct(A)]
+    pub field: u32
+}
+
+
+fn main() {}
\ No newline at end of file

From 1c46a7cfcdd7781bab1f5d3efab1192ee19901d9 Mon Sep 17 00:00:00 2001
From: Sean Lynch <42618346+swlynch99@users.noreply.github.com>
Date: Mon, 18 Aug 2025 13:08:37 -0700
Subject: [PATCH 2/4] formatting

---
 tests/ui/fail/inaccessible-field.rs     | 1 -
 tests/ui/fail/multiple-attr-on-field.rs | 1 -
 tests/ui/fail/multiple-errors.rs        | 2 +-
 tests/ui/pass/expression-vis.rs         | 5 +----
 tests/ui/pass/no-warn-pub-self.rs       | 5 ++---
 5 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/tests/ui/fail/inaccessible-field.rs b/tests/ui/fail/inaccessible-field.rs
index c11b59a..5c47fd3 100644
--- a/tests/ui/fail/inaccessible-field.rs
+++ b/tests/ui/fail/inaccessible-field.rs
@@ -1,4 +1,3 @@
-
 mod inner {
     use substruct::substruct;
 
diff --git a/tests/ui/fail/multiple-attr-on-field.rs b/tests/ui/fail/multiple-attr-on-field.rs
index e816e9e..2c86bc6 100644
--- a/tests/ui/fail/multiple-attr-on-field.rs
+++ b/tests/ui/fail/multiple-attr-on-field.rs
@@ -5,7 +5,6 @@ struct A {
     #[substruct(B)]
     #[substruct(C)]
     field: u32,
-
 }
 
 fn main() {}
diff --git a/tests/ui/fail/multiple-errors.rs b/tests/ui/fail/multiple-errors.rs
index 35c7c44..07b8155 100644
--- a/tests/ui/fail/multiple-errors.rs
+++ b/tests/ui/fail/multiple-errors.rs
@@ -4,7 +4,7 @@ use substruct::substruct;
 pub struct A {
     #[substruct_attr(blah, blah, blah)]
     #[substruct_attr(blah, bleh, blah)]
-    pub x: u32
+    pub x: u32,
 }
 
 fn main() {}
diff --git a/tests/ui/pass/expression-vis.rs b/tests/ui/pass/expression-vis.rs
index 78cdb93..3b8df8c 100644
--- a/tests/ui/pass/expression-vis.rs
+++ b/tests/ui/pass/expression-vis.rs
@@ -1,12 +1,9 @@
-
-
 mod inner {
     use substruct::substruct;
 
     #[substruct(A, B)]
     #[derive(Default)]
-    pub struct Test
-    {
+    pub struct Test {
         #[substruct(pub any(A, B))]
         field: u32,
     }
diff --git a/tests/ui/pass/no-warn-pub-self.rs b/tests/ui/pass/no-warn-pub-self.rs
index 9e9b236..b929bf5 100644
--- a/tests/ui/pass/no-warn-pub-self.rs
+++ b/tests/ui/pass/no-warn-pub-self.rs
@@ -6,8 +6,7 @@ use substruct::substruct;
 #[substruct(pub(self) A)]
 pub struct Test {
     #[substruct(A)]
-    pub field: u32
+    pub field: u32,
 }
 
-
-fn main() {}
\ No newline at end of file
+fn main() {}

From 535c6ae71a3ead787c228eb009c0412b2e4c3434 Mon Sep 17 00:00:00 2001
From: Sean Lynch <42618346+swlynch99@users.noreply.github.com>
Date: Mon, 18 Aug 2025 13:11:01 -0700
Subject: [PATCH 3/4] Fix test line numbers

---
 tests/ui/fail/inaccessible-field.stderr | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/ui/fail/inaccessible-field.stderr b/tests/ui/fail/inaccessible-field.stderr
index 4c83cd6..c34e86a 100644
--- a/tests/ui/fail/inaccessible-field.stderr
+++ b/tests/ui/fail/inaccessible-field.stderr
@@ -1,5 +1,5 @@
 error[E0616]: field `field1` of struct `inner::A` is private
-  --> tests/ui/fail/inaccessible-field.rs:18:24
+  --> tests/ui/fail/inaccessible-field.rs:17:24
    |
-18 |     let _field = value.field1;
+17 |     let _field = value.field1;
    |                        ^^^^^^ private field

From 54e8fb8ca49151b87ae78e20a568ee536453776d Mon Sep 17 00:00:00 2001
From: Sean Lynch <42618346+swlynch99@users.noreply.github.com>
Date: Mon, 18 Aug 2025 13:15:32 -0700
Subject: [PATCH 4/4] Update test cases for stable rustc

---
 tests/ui/fail/inaccessible-struct.stderr | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tests/ui/fail/inaccessible-struct.stderr b/tests/ui/fail/inaccessible-struct.stderr
index 0531998..168f898 100644
--- a/tests/ui/fail/inaccessible-struct.stderr
+++ b/tests/ui/fail/inaccessible-struct.stderr
@@ -7,11 +7,11 @@ error[E0603]: struct `A` is private
 note: the struct `A` is defined here
   --> tests/ui/fail/inaccessible-struct.rs:4:17
    |
- 4 |       #[substruct(pub(self) A)]
+4  |       #[substruct(pub(self) A)]
    |  _________________^
- 5 | |     #[derive(Default)]
- 6 | |     pub struct Test {
- 7 | |         #[substruct(A)]
- 8 | |         pub field: u32,
- 9 | |     }
+5  | |     #[derive(Default)]
+6  | |     pub struct Test {
+7  | |         #[substruct(A)]
+8  | |         pub field: u32,
+9  | |     }
    | |_____^