chore(aztec-nr): Public self constructor function to prevent static byte code size blow up (#23062)

Resolves
[F-637](https://linear.app/aztec-labs/issue/F-637/aztec-nr-macros-contain-self-construction-to-a-function-to-prevent)

Stacks on #23061

- New `generate_public_self_creator` emits a per-contract
`__aztec_nr_internals__create_public_self<let N: u32>()` helper
- `generate_public_external` now emits a single call to it instead of
inlining the preamble. This can be seen in the snapshots.
- Helper is emitted from `process_functions` and gated on
`public_functions.len() > 0`

~~Improvements tested locally:~~

I need to test further. Either way this is cleaner macro code.

Author: vezenovm

noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr

@@ -6,9 +6,52 @@ use crate::macros::{
     },
 };
 
+/// Generates the per-contract helper that builds public `self`.
+///
+/// Each public external function calls this helper instead of inlining the construction, so the same preamble does not
+/// appear duplicated in every public function body. We let Noir's inliner decide whether to inline the helper at each
+/// call site rather than forcing it via macro expansion.
+///
+/// The helper is generic over the calldata length `N` because `PublicContext::new` takes a closure that reads `N`
+/// fields from calldata. Noir monomorphizes one copy per distinct `N`, so public functions with the same number of
+/// serialized args reuse the same compiled code.
+pub(crate) comptime fn generate_public_self_creator(m: Module) -> Quoted {
+    let (storage_type, storage_init) = if module_has_storage(m) {
+        (quote { Storage<aztec::context::PublicContext> }, quote { let storage = Storage::init(context); })
+    } else {
+        // Contract does not have Storage defined, so we set storage to the unit type `()`. ContractSelfPublic requires
+        // a storage struct in its constructor. Using an Option type would lead to worse developer experience and
+        // higher constraint counts so we use the unit type `()` instead.
+        (quote { () }, quote { let storage = (); })
+    };
+
+    quote {
+        #[contract_library_method]
+        unconstrained fn __aztec_nr_internals__create_public_self<let N: u32>() -> aztec::contract_self::ContractSelfPublic<
+            $storage_type,
+            CallSelf<aztec::context::PublicContext>,
+            CallSelfStatic<aztec::context::PublicContext>,
+            CallInternal<aztec::context::PublicContext>,
+        > {
+            // Unlike in the private case, in public the `context` does not need to receive the hash of the original
+            // params.
+            let context = aztec::context::PublicContext::new(|| {
+                // We start from 1 because we skip the selector for the dispatch function.
+                let serialized_args : [Field; N] = aztec::oracle::avm::calldata_copy(1, N);
+                aztec::hash::hash_args(serialized_args)
+            });
+            $storage_init
+            let self_address = context.this_address();
+            let call_self: CallSelf<aztec::context::PublicContext> = CallSelf { address: self_address, context };
+            let call_self_static: CallSelfStatic<aztec::context::PublicContext> = CallSelfStatic { address: self_address, context };
+            let internal: CallInternal<aztec::context::PublicContext> = CallInternal { context };
+            aztec::contract_self::ContractSelfPublic::new(context, storage, call_self, call_self_static, internal)
+        }
+    }
+}
+
 pub(crate) comptime fn generate_public_external(f: FunctionDefinition) -> Quoted {
     let module_has_initializer = module_has_initializer(f.module());
-    let module_has_storage = module_has_storage(f.module());
 
     // Public functions undergo a lot of transformations from their Aztec.nr form.
     let original_params = f.parameters();
@@ -28,35 +71,9 @@ pub(crate) comptime fn generate_public_external(f: FunctionDefinition) -> Quoted
             .join(quote {+})
     };
 
-    let storage_init = if module_has_storage {
-        quote {
-            let storage = Storage::init(context);
-        }
-    } else {
-        // Contract does not have Storage defined, so we set storage to the unit type `()`. ContractSelfPublic requires
-        // a storage struct in its constructor. Using an Option type would lead to worse developer experience and
-        // higher constraint counts so we use the unit type `()` instead.
-        quote {
-            let storage = ();
-        }
-    };
-
-    // Unlike in the private case, in public the `context` does not need to receive the hash of the original params.
     let contract_self_creation = quote {
         #[allow(unused_variables)]
-        let mut self = {
-            let context = aztec::context::PublicContext::new(|| {
-            // We start from 1 because we skip the selector for the dispatch function.
-            let serialized_args : [Field; $args_len_quote] = aztec::oracle::avm::calldata_copy(1, $args_len_quote);
-            aztec::hash::hash_args(serialized_args)
-            });
-            $storage_init
-            let self_address = context.this_address();
-            let call_self: CallSelf<aztec::context::PublicContext> = CallSelf { address: self_address, context };
-            let call_self_static: CallSelfStatic<aztec::context::PublicContext> = CallSelfStatic { address: self_address, context };
-            let internal: CallInternal<aztec::context::PublicContext> = CallInternal { context };
-            aztec::contract_self::ContractSelfPublic::new(context, storage, call_self, call_self_static, internal)
-        };
+        let mut self = __aztec_nr_internals__create_public_self::<$args_len_quote>();
     };
 
     let original_function_name = f.name();

noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr

@@ -12,7 +12,9 @@ pub(crate) mod internal;
 
 use abi_export::create_fn_abi_export;
 use external::{
-    private::generate_private_external, public::generate_public_external, utility::generate_utility_external,
+    private::generate_private_external,
+    public::{generate_public_external, generate_public_self_creator},
+    utility::generate_utility_external,
 };
 use internal::{generate_private_internal, generate_public_internal};
 
@@ -47,6 +49,15 @@ pub(crate) comptime fn process_functions(m: Module) -> Quoted {
     let transformed_utility_functions =
         utility_functions.map(|function| generate_utility_external(function)).join(quote {});
 
+    // Emit a contract-level helper that constructs `self` for public functions. Each transformed public function calls
+    // this helper rather than inlining the preamble. The helper is only useful for public external functions, so we
+    // skip emitting it when the contract has none.
+    let public_self_creator = if public_functions.len() > 0 {
+        generate_public_self_creator(m)
+    } else {
+        quote {}
+    };
+
     // Now that we have generated quotes of the new functions based on the original function definitions, we replace
     // the original functions' bodies with `static_assert(false, ...)` to prevent them from being called directly from
     // within the contract. We also need to set the return type to `()` to avoid compilation errors.
@@ -84,6 +95,7 @@ pub(crate) comptime fn process_functions(m: Module) -> Quoted {
 
     // We return the new functions' quotes to be injected into the contract.
     quote {
+        $public_self_creator
         $transformed_private_functions
         $transformed_public_functions
         $transformed_utility_functions

noir-projects/contract-snapshots/tests/snapshots/compile_failure/authorize_once_from_wrong_type/snapshots__stderr.snap

@@ -14,13 +14,13 @@ error: Argument from in function foo must be of type AztecAddress, but is of typ
     2: aztec
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/aztec.nr:97:21
     3: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:9
     4: [T]::map
             at std/vector.nr:67:33
     5: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:41
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:41
     6: generate_public_external
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:97:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:114:9
     7: create_authorize_once_check
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr:72:9
 

noir-projects/contract-snapshots/tests/snapshots/compile_failure/authorize_once_missing_from_param/snapshots__stderr.snap

@@ -14,13 +14,13 @@ error: Function foo does not have a from parameter. Please specify which one to
     2: aztec
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/aztec.nr:97:21
     3: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:9
     4: [T]::map
             at std/vector.nr:67:33
     5: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:41
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:41
     6: generate_public_external
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:97:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:114:9
     7: create_authorize_once_check
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr:67:9
 

noir-projects/contract-snapshots/tests/snapshots/compile_failure/authorize_once_missing_nonce_param/snapshots__stderr.snap

@@ -14,13 +14,13 @@ error: Function foo does not have a authwit_nonce. Please specify which one to u
     2: aztec
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/aztec.nr:97:21
     3: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:9
     4: [T]::map
             at std/vector.nr:67:33
     5: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:41
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:41
     6: generate_public_external
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:97:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:114:9
     7: create_authorize_once_check
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr:81:9
 

noir-projects/contract-snapshots/tests/snapshots/compile_failure/authorize_once_nonce_wrong_type/snapshots__stderr.snap

@@ -14,13 +14,13 @@ error: Argument authwit_nonce in function foo must be of type Field, but is of t
     2: aztec
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/aztec.nr:97:21
     3: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:9
     4: [T]::map
             at std/vector.nr:67:33
     5: process_functions
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:46:41
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/mod.nr:48:41
     6: generate_public_external
-            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:97:9
+            at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/public.nr:114:9
     7: create_authorize_once_check
             at <repo>/noir-projects/aztec-nr/aztec/src/macros/internals_functions_generation/external/helpers.nr:86:9