1 files changed, 115 insertions, 0 deletions
diff --git a/rola-vcs/internal_macros/src/constants.rs b/rola-vcs/internal_macros/src/constants.rs
new file mode 100644
index 0000000..2e76bfe
--- /dev/null
+++ b/rola-vcs/internal_macros/src/constants.rs
@@ -0,0 +1,115 @@
+use proc_macro::TokenStream;
+use quote::{format_ident, quote};
+use syn::{Expr, Item, ItemConst, ItemMod, Lit, parse_macro_input, parse_quote};
+
+/// Entry point called from lib.rs.
+pub fn expand(_attr: TokenStream, item: TokenStream) -> TokenStream {
+    let mut input_mod = parse_macro_input!(item as ItemMod);
+
+    let (_, items) = match &mut input_mod.content {
+        Some(content) => content,
+        None => panic!("#[constants] can only be applied to a module with a body"),
+    };
+
+    let mut new_items: Vec<Item> = Vec::with_capacity(items.len());
+
+    for item in items.iter() {
+        if let Item::Const(const_item) = item {
+            let func = transform_const(const_item);
+            new_items.push(func);
+        } else {
+            new_items.push(item.clone());
+        }
+    }
+
+    let mod_ident = &input_mod.ident;
+    let vis = &input_mod.vis;
+
+    let output = quote! {
+        #[allow(non_snake_case)]
+        #vis mod #mod_ident {
+            #(#new_items)*
+        }
+    };
+
+    output.into()
+}
+
+/// Transforms a single `const` item into a function.
+fn transform_const(const_item: &ItemConst) -> Item {
+    let name = &const_item.ident;
+    let attrs = &const_item.attrs;
+
+    // Extract the string literal value from the const
+    let value_str = match &*const_item.expr {
+        Expr::Lit(expr_lit) => match &expr_lit.lit {
+            Lit::Str(lit_str) => lit_str.value(),
+            _ => panic!(
+                "#[constants] only supports `&str` literals, \
+                 but `{name}` has a non-string literal"
+            ),
+        },
+        _ => panic!(
+            "#[constants] only supports literal expressions, \
+             but `{name}` has a non-literal expression"
+        ),
+    };
+
+    let placeholders = extract_placeholders(&value_str);
+
+    if placeholders.is_empty() {
+        parse_quote! {
+            #(#attrs)*
+            pub fn #name() -> String {
+                #value_str.to_string()
+            }
+        }
+    } else {
+        let params: Vec<_> = placeholders
+            .iter()
+            .map(|p| {
+                let ident = format_ident!("{p}");
+                quote! { #ident: impl ::core::convert::AsRef<str> }
+            })
+            .collect();
+
+        let format_args: Vec<_> = placeholders
+            .iter()
+            .map(|p| {
+                let ident = format_ident!("{p}");
+                quote! { #ident = #ident.as_ref() }
+            })
+            .collect();
+
+        parse_quote! {
+            #(#attrs)*
+            pub fn #name(#(#params),*) -> String {
+                ::std::format!(#value_str, #(#format_args),*)
+            }
+        }
+    }
+}
+
+/// Extracts all `{name}` placeholder identifiers from a format string.
+fn extract_placeholders(s: &str) -> Vec<String> {
+    let mut placeholders = Vec::new();
+    let mut chars = s.char_indices().peekable();
+
+    while let Some((_, c)) = chars.next() {
+        if c == '{' {
+            let mut name = String::new();
+            for (_, c) in &mut chars {
+                if c == '}' {
+                    break;
+                }
+                name.push(c);
+            }
+            let trimmed = name.trim().to_string();
+            if !trimmed.is_empty() {
+                placeholders.push(trimmed);
+            }
+        }
+    }
+
+    placeholders
+}