commit 143b9c84de8cf9cf0e08f4007c5c380435827731
Author: Uttarayan Mondal <email@uttarayan.me>
Date:   Fri Aug 11 11:42:42 2023 +0530

    [init] Initial commit

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4fffb2f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..62b3910
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,24 @@
+[workspace.package]
+version = "0.1.0"
+edition = "2021"
+repository = "https://github.com/uttarayan21/comptime-builder"
+documentation = "https://docs.rs/comptime-builder"
+
+[workspace]
+members = [
+    ".",
+    "comptime-builder-macros"
+]
+
+[workspace.dependencies]
+comptime-builder-macros = { version = "0.1.0", path = "comptime-builder-macros" }
+
+[package]
+name = "comptime-builder"
+version.workspace = true
+edition.workspace = true
+repository.workspace = true
+documentation.workspace = true
+
+[dependencies]
+comptime-builder-macros.workspace = true
diff --git a/comptime-builder-macros/Cargo.toml b/comptime-builder-macros/Cargo.toml
new file mode 100644
index 0000000..e91760f
--- /dev/null
+++ b/comptime-builder-macros/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "comptime-builder-macros"
+version.workspace = true
+edition.workspace = true
+repository.workspace = true
+documentation.workspace = true
+
+[dependencies]
+convert_case = "0.6.0"
+proc-macro2 = "1.0.66"
+quote = "1.0.32"
+syn = { version = "2.0.27", features = ["extra-traits", "full"] }
+
+[lib]
+proc-macro = true
diff --git a/comptime-builder-macros/src/lib.rs b/comptime-builder-macros/src/lib.rs
new file mode 100644
index 0000000..c43dcbb
--- /dev/null
+++ b/comptime-builder-macros/src/lib.rs
@@ -0,0 +1,149 @@
+use syn::*;
+
+#[proc_macro_derive(Builder)]
+pub fn builder_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    let input = parse_macro_input!(input as DeriveInput);
+
+    dbg!(derive_builder::derive(input)
+        .unwrap_or_else(|err| err.into_compile_error())
+        .into())
+}
+
+mod derive_builder {
+    use proc_macro2::*;
+    use quote::quote;
+    use syn::punctuated::Punctuated;
+    use syn::token::Comma;
+    use syn::*;
+
+    pub fn derive(input: DeriveInput) -> Result<TokenStream> {
+        let crate_name: syn::Path = parse_quote!(::comptime_builder);
+        let fields = match input.data {
+            Data::Struct(DataStruct {
+                fields: Fields::Named(FieldsNamed { named, .. }),
+                ..
+            }) => named,
+            _ => {
+                return Err(syn::Error::new_spanned(
+                    input,
+                    "expected a struct with named fields",
+                ))
+            }
+        };
+
+        let struct_name = &input.ident;
+        let builder_struct_name = Ident::new(&format!("{}Builder", struct_name), Span::call_site());
+
+        // Use Generic type T{0..} to represent the fields
+        let mut state = 1u32;
+        let generic_fields = fields.into_iter().scan(&mut state, |state, mut field| {
+            let gtype = format!("T{}", state);
+            **state += 1;
+            field.ty = syn::Type::Path(TypePath {
+                qself: None,
+                path: syn::Path {
+                    leading_colon: None,
+                    segments: Punctuated::from_iter(vec![PathSegment {
+                        ident: syn::Ident::new(&gtype, Span::call_site()),
+                        arguments: PathArguments::None,
+                    }]),
+                },
+            });
+            Some(field)
+        });
+        let generic_fields: Punctuated<Field, Comma> = generic_fields.collect();
+        let builder_generics = syn::Generics {
+            lt_token: Token![<](Span::call_site()).into(),
+            params: (1..state)
+                .map(|f| {
+                    GenericParam::Type(TypeParam {
+                        attrs: vec![],
+                        ident: syn::Ident::new(&format!("T{}", f), Span::call_site()),
+                        colon_token: None,
+                        bounds: Punctuated::new(),
+                        eq_token: None,
+                        default: None,
+                    })
+                })
+                .collect(),
+            gt_token: Token![>](Span::call_site()).into(),
+            where_clause: None,
+        };
+
+        let builder_struct = syn::ItemStruct {
+            attrs: vec![],
+            vis: Visibility::Inherited,
+            struct_token: Token![struct](Span::call_site()),
+            ident: builder_struct_name.clone(),
+            fields: Fields::Named(FieldsNamed {
+                brace_token: token::Brace::default(),
+                named: generic_fields,
+            }),
+            generics: builder_generics,
+            semi_token: None,
+        };
+
+        let empty_builder_type: syn::Type = syn::Type::Path(TypePath {
+            qself: None,
+            path: syn::Path {
+                leading_colon: None,
+                segments: Punctuated::from_iter(vec![PathSegment {
+                    ident: builder_struct_name.clone(),
+                    arguments: PathArguments::AngleBracketed(AngleBracketedGenericArguments {
+                        colon2_token: None,
+                        lt_token: Token![<](Span::call_site()),
+                        args: core::iter::repeat::<GenericArgument>(parse_quote!(
+                            #crate_name::Empty
+                        ))
+                        .take(state as usize - 1)
+                        .collect(),
+                        gt_token: Token![>](Span::call_site()),
+                    }),
+                }]),
+            },
+        });
+
+        let empty_builder = syn::ExprStruct {
+            attrs: vec![],
+            qself: None,
+            path: parse_quote!(#builder_struct_name),
+            brace_token: token::Brace::default(),
+            fields: core::iter::repeat::<FieldValue>(parse_quote!(
+                _field: #crate_name::Empty
+            ))
+            .take(state as usize - 1)
+            .collect(),
+            dot2_token: None,
+            rest: None,
+        };
+
+        let empty_builder_fn = syn::ImplItemFn {
+            attrs: vec![],
+            vis: Visibility::Inherited,
+            defaultness: None,
+            sig: parse_quote!(fn builder() -> #empty_builder_type),
+            block: parse_quote! {{
+                #empty_builder
+            }},
+        };
+
+        let ge = input.generics.params.clone();
+        let self_ty = parse_quote!(#struct_name<#ge>);
+        let impl_empty_builder_fn = syn::ItemImpl {
+            attrs: vec![],
+            defaultness: None,
+            unsafety: None,
+            impl_token: Token![impl](Span::call_site()),
+            generics: input.generics.clone(),
+            trait_: None,
+            self_ty: Box::new(self_ty),
+            brace_token: token::Brace::default(),
+            items: vec![ImplItem::Fn(empty_builder_fn)],
+        };
+
+        Ok(quote! {
+            #impl_empty_builder_fn
+            #builder_struct
+        })
+    }
+}
diff --git a/examples/date.rs b/examples/date.rs
new file mode 100644
index 0000000..3e219a3
--- /dev/null
+++ b/examples/date.rs
@@ -0,0 +1,101 @@
+use comptime_builder::*;
+
+impl<Y, M, D> WithField<1, u16, Date> for DateBuilder<Y, M, D> {
+    type Output = DateBuilder<Field<1, u16>, M, D>;
+    fn with_field(self, value: u16) -> Self::Output {
+        DateBuilder {
+            year: Field(value),
+            month: self.month,
+            day: self.day,
+        }
+    }
+}
+
+impl<Y, M, D> WithField<2, u8, Date> for DateBuilder<Y, M, D> {
+    type Output = DateBuilder<Y, Field<2, u8>, D>;
+    fn with_field(self, value: u8) -> Self::Output {
+        DateBuilder {
+            year: self.year,
+            month: Field(value),
+            day: self.day,
+        }
+    }
+}
+
+impl<Y, M, D> WithField<3, u8, Date> for DateBuilder<Y, M, D> {
+    type Output = DateBuilder<Y, M, Field<3, u8>>;
+    fn with_field(self, value: u8) -> Self::Output {
+        DateBuilder {
+            year: self.year,
+            month: self.month,
+            day: Field(value),
+        }
+    }
+}
+
+pub trait WithYear: WithField<1, u16, Date> {
+    fn with_year(self, value: u16) -> Self::Output {
+        self.with_field(value)
+    }
+}
+
+impl<T> WithYear for T where T: WithField<1, u16, Date> {}
+
+pub trait WithMonth: WithField<2, u8, Date> {
+    fn with_month(self, value: u8) -> Self::Output {
+        self.with_field(value)
+    }
+}
+
+impl<T> WithMonth for T where T: WithField<2, u8, Date> {}
+
+pub trait WithDay: WithField<3, u8, Date> {
+    fn with_day(self, value: u8) -> Self::Output {
+        self.with_field(value)
+    }
+}
+
+impl<T> WithDay for T where T: WithField<3, u8, Date> {}
+
+pub struct DateBuilder<Year, Month, Day> {
+    year: Year,
+    month: Month,
+    day: Day,
+}
+
+impl DateBuilder<Field<1, u16>, Field<2, u8>, Field<3, u8>> {
+    fn build(self) -> Date {
+        Date {
+            year: self.year.0,
+            month: self.month.0,
+            day: self.day.0,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct Date {
+    year: u16,
+    month: u8,
+    day: u8,
+}
+pub struct Empty;
+
+impl Date {
+    pub fn builder() -> DateBuilder<Empty, Empty, Empty> {
+        DateBuilder {
+            year: Empty,
+            month: Empty,
+            day: Empty,
+        }
+    }
+}
+
+pub fn main() {
+    let date = Date::builder()
+        .with_year(2022)
+        .with_month(5)
+        .with_day(1)
+        .build();
+    dbg!(date);
+}
diff --git a/examples/derive.rs b/examples/derive.rs
new file mode 100644
index 0000000..7d5b9be
--- /dev/null
+++ b/examples/derive.rs
@@ -0,0 +1,12 @@
+use comptime_builder::Builder;
+
+#[derive(Builder)]
+pub struct MyStruct<T1, T2> {
+    pub my_field: T1,
+    pub my_other_field: T2,
+    pub our_field: String,
+}
+
+pub fn main() {
+    
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..d1ee22c
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,13 @@
+pub use comptime_builder_macros::Builder;
+
+pub struct Empty;
+
+
+pub trait HasField<const N: usize, T> {}
+impl<const N: usize, T> HasField<N, T> for Field<N, T> {}
+pub struct Field<const N: usize, T>(pub T);
+
+pub trait WithField<const N: usize, Field, Struct>: Sized {
+    type Output;
+    fn with_field(self, value: Field) -> Self::Output;
+}