Fix trait method call resolution in contractimpl (#1729)

### What
Use fully qualified syntax (`<Type as Trait>::func()`) in
macro-generated WASM exports when `#[contractimpl]` is applied to a
trait impl block.

### Why
Rust's name resolution prefers inherent methods over trait methods when
using `<Type>::func()` syntax. If a contract type has both an inherent
method and a trait method with the same name, the generated export
incorrectly calls the inherent method instead of the trait method the
`#[contractimpl]` block is defined for.

(cherry picked from commit e92a393)
(cherry picked from commit 347f711)

Author: leighmcculloch

soroban-sdk-macros/src/derive_fn.rs

@@ -17,7 +17,7 @@ pub fn derive_pub_fn(
     ident: &Ident,
     attrs: &[Attribute],
     inputs: &Punctuated<FnArg, Comma>,
-    trait_ident: Option<&Ident>,
+    _trait_ident: Option<&Ident>,
     client_ident: &str,
 ) -> Result<TokenStream2, TokenStream2> {
     // Collect errors as they are encountered and emit them at the end.
@@ -114,11 +114,6 @@ pub fn derive_pub_fn(
     };
     let slice_args: Vec<TokenStream2> = (0..wrap_args.len()).map(|n| quote! { args[#n] }).collect();
     let arg_count = slice_args.len();
-    let use_trait = if let Some(t) = trait_ident {
-        quote! { use super::#t }
-    } else {
-        quote! {}
-    };
 
     // If errors have occurred, render them instead.
     if !errors.is_empty() {
@@ -159,7 +154,6 @@ pub fn derive_pub_fn(
 
             #[deprecated(note = #deprecated_note)]
             pub fn invoke_raw(env: #crate_path::Env, #(#wrap_args),*) -> #crate_path::Val {
-                #use_trait;
                 <_ as #crate_path::IntoVal<#crate_path::Env, #crate_path::Val>>::into_val(
                     #[allow(deprecated)]
                     &#call(

soroban-sdk-macros/src/lib.rs

@@ -241,7 +241,11 @@ pub fn contractimpl(metadata: TokenStream, input: TokenStream) -> TokenStream {
         .iter()
         .map(|m| {
             let ident = &m.sig.ident;
-            let call = quote! { <super::#ty>::#ident };
+            let call = if let Some(t) = trait_ident {
+                quote! { <super::#ty as #t>::#ident }
+            } else {
+                quote! { <super::#ty>::#ident }
+            };
             derive_pub_fn(
                 crate_path,
                 &call,

soroban-sdk/src/tests.rs

@@ -24,6 +24,7 @@ mod contract_udt_enum_option;
 mod contract_udt_option;
 mod contract_udt_struct;
 mod contract_udt_struct_tuple;
+mod contractimpl_trait_call_resolution;
 mod contractimport;
 mod contractimport_with_error;
 mod cost_estimate;

soroban-sdk/src/tests/contractimpl_trait_call_resolution.rs

@@ -0,0 +1,53 @@
+use crate as soroban_sdk;
+use soroban_sdk::{contract, contractimpl, Env};
+
+// ---------------------------------------------------------------------------
+// Test: when #[contractimpl] is applied to `impl Trait for Type`, the
+// generated WASM export must call the *trait* associated function, not an
+// inherent associated function that happens to share the same name.
+//
+// Rust's name-resolution rules say that `<Type>::func()` resolves to the
+// inherent associated function when one exists, even if a trait with the
+// same function is in scope.  The only way to force the trait version is
+// Universal Function Call Syntax: `<Type as Trait>::func()`.
+//
+// This test creates a contract where both the inherent and trait versions
+// of `value` return a different u32.  We then check which value was
+// returned to determine which function was called.
+// ---------------------------------------------------------------------------
+
+#[contract]
+pub struct Contract;
+
+/// Inherent function — returns 1.
+impl Contract {
+    pub fn value(_env: Env) -> u32 {
+        1
+    }
+}
+
+pub trait ContractTrait {
+    fn value(env: Env) -> u32;
+}
+
+/// Trait implementation — returns 2.
+/// The macro-generated WASM export for "value" MUST call this version.
+#[contractimpl]
+impl ContractTrait for Contract {
+    fn value(_env: Env) -> u32 {
+        2
+    }
+}
+
+/// The exported `value` entry point must call the trait function, which
+/// returns 2.
+#[test]
+fn calls_trait_fn() {
+    let e = Env::default();
+    let contract_id = e.register(Contract, ());
+    let client = ContractClient::new(&e, &contract_id);
+
+    let result = client.value();
+
+    assert_eq!(result, 2);
+}

soroban-sdk/test_snapshots/tests/contractimpl_trait_call_resolution/calls_trait_fn.1.json

@@ -0,0 +1,76 @@
+{
+  "generators": {
+    "address": 1,
+    "nonce": 0
+  },
+  "auth": [
+    [],
+    []
+  ],
+  "ledger": {
+    "protocol_version": 22,
+    "sequence_number": 0,
+    "timestamp": 0,
+    "network_id": "0000000000000000000000000000000000000000000000000000000000000000",
+    "base_reserve": 0,
+    "min_persistent_entry_ttl": 4096,
+    "min_temp_entry_ttl": 16,
+    "max_entry_ttl": 6312000,
+    "ledger_entries": [
+      [
+        {
+          "contract_data": {
+            "contract": "CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD2KM",
+            "key": "ledger_key_contract_instance",
+            "durability": "persistent"
+          }
+        },
+        [
+          {
+            "last_modified_ledger_seq": 0,
+            "data": {
+              "contract_data": {
+                "ext": "v0",
+                "contract": "CAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAD2KM",
+                "key": "ledger_key_contract_instance",
+                "durability": "persistent",
+                "val": {
+                  "contract_instance": {
+                    "executable": {
+                      "wasm": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+                    },
+                    "storage": null
+                  }
+                }
+              }
+            },
+            "ext": "v0"
+          },
+          4095
+        ]
+      ],
+      [
+        {
+          "contract_code": {
+            "hash": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+          }
+        },
+        [
+          {
+            "last_modified_ledger_seq": 0,
+            "data": {
+              "contract_code": {
+                "ext": "v0",
+                "hash": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+                "code": ""
+              }
+            },
+            "ext": "v0"
+          },
+          4095
+        ]
+      ]
+    ]
+  },
+  "events": []
+}