[gcc r17-5154] gccrs: Improve bodyless function pattern check

[Marc Poulhies via Gcc-cvs]

https://gcc.gnu.org/g:dcf3cbc0f78de4834914895122d70530c3ffd775

commit r17-5154-gdcf3cbc0f78de4834914895122d70530c3ffd775
Author: Owen Avery <powerboat9.ga...@gmail.com>
Date:   Sun Sep 20 19:10:08 2026 -0400

    gccrs: Improve bodyless function pattern check
    
    gcc/rust/ChangeLog:
    
            * checks/errors/rust-ast-validation.cc
            (ASTValidation::visit (Function)): Emit error on complex
            patterns in non-extern bodyless functions as well.
    
    gcc/testsuite/ChangeLog:
    
            * rust/compile/function-param-bodyless.rs: New test.
    
    Signed-off-by: Owen Avery <powerboat9.ga...@gmail.com>

Diff:
---
 gcc/rust/checks/errors/rust-ast-validation.cc      | 49 ++++++++++++++++------
 .../rust/compile/function-param-bodyless.rs        | 35 ++++++++++++++++
 2 files changed, 72 insertions(+), 12 deletions(-)

diff --git a/gcc/rust/checks/errors/rust-ast-validation.cc 
b/gcc/rust/checks/errors/rust-ast-validation.cc
index b2825fb2c958..e5f8577cbabb 100644
--- a/gcc/rust/checks/errors/rust-ast-validation.cc
+++ b/gcc/rust/checks/errors/rust-ast-validation.cc
@@ -104,6 +104,35 @@ ASTValidation::visit (AST::Function &function)
       function.get_self_param ().get_locus (),
       "%<self%> parameter is only allowed in associated functions");
 
+  // functions without bodies can only have very specific
+  // kinds of patterns in their parameters
+  auto is_param_complex_with_loc
+    = [] (AST::Param &param) -> tl::optional<location_t> {
+    tl::optional<location_t> ret;
+
+    if (param.is_self () || param.is_variadic ())
+      return ret;
+
+    auto &fn_param = static_cast<AST::FunctionParam &> (param);
+    if (!fn_param.has_name ())
+      return ret;
+
+    auto &pat = fn_param.get_pattern ();
+    ret = pat.get_locus ();
+    auto kind = pat.get_pattern_kind ();
+    if (kind == AST::Pattern::Kind::Identifier)
+      {
+       auto &ident_pat = static_cast<AST::IdentifierPattern &> (pat);
+       if (!ident_pat.get_is_ref () && !ident_pat.get_is_mut ()
+           && !ident_pat.has_subpattern ())
+         ret = tl::nullopt;
+      }
+    else if (kind == AST::Pattern::Kind::Wildcard)
+      ret = tl::nullopt;
+
+    return ret;
+  };
+
   if (function.is_external ())
     {
       if (function.has_body ())
@@ -123,20 +152,11 @@ ASTValidation::visit (AST::Function &function)
              it->get ()->get_locus (),
              "%<...%> must be the last argument of a C-variadic function");
 
-         // if functional parameter
-         if (!it->get ()->is_self () && !it->get ()->is_variadic ())
-           {
-             auto &param = static_cast<AST::FunctionParam &> (**it);
-             auto kind = param.get_pattern ().get_pattern_kind ();
-
-             if (kind != AST::Pattern::Kind::Identifier
-                 && kind != AST::Pattern::Kind::Wildcard)
-               rust_error_at (it->get ()->get_locus (), ErrorCode::E0130,
-                              "pattern not allowed in foreign function");
-           }
+         if (auto pat_loc = is_param_complex_with_loc (**it))
+           rust_error_at (*pat_loc, ErrorCode::E0130,
+                          "pattern not allowed in foreign function");
        }
     }
-
   else
     {
       if (!function.has_body ())
@@ -158,6 +178,11 @@ ASTValidation::visit (AST::Function &function)
              it->get ()->get_locus (),
              "only foreign or %<unsafe extern \"C\"%> functions may "
              "be C-variadic");
+
+         if (!function.has_body ())
+           if (auto pat_loc = is_param_complex_with_loc (**it))
+             rust_error_at (*pat_loc, ErrorCode::E0642,
+                            "pattern not allowed in function without body");
        }
     }
 
diff --git a/gcc/testsuite/rust/compile/function-param-bodyless.rs 
b/gcc/testsuite/rust/compile/function-param-bodyless.rs
new file mode 100644
index 000000000000..eb71d475beba
--- /dev/null
+++ b/gcc/testsuite/rust/compile/function-param-bodyless.rs
@@ -0,0 +1,35 @@
+// { dg-additional-options "-w" }
+#![feature(no_core)]
+#![no_core]
+
+mod extern_test {
+    extern "C" {
+        // { dg-error "pattern not allowed in foreign function .E0130." "" { 
target *-*-* } .+1 }
+        fn f1(mut a: i32);
+        // { dg-error "pattern not allowed in foreign function .E0130." "" { 
target *-*-* } .+1 }
+        fn f2(ref a: i32);
+        // { dg-error "pattern not allowed in foreign function .E0130." "" { 
target *-*-* } .+1 }
+        fn f3(a @ _: i32);
+        // { dg-error "pattern not allowed in foreign function .E0130." "" { 
target *-*-* } .+1 }
+        fn f4((a,): i32);
+        // { dg-error "pattern not allowed in foreign function .E0130." "" { 
target *-*-* } .+1 }
+        fn f5((a): i32);
+
+        fn f6(_: i32);
+    }
+}
+
+trait Foo {
+    // { dg-error "pattern not allowed in function without body .E0642." "" { 
target *-*-* } .+1 }
+    fn f1(mut a: i32);
+    // { dg-error "pattern not allowed in function without body .E0642." "" { 
target *-*-* } .+1 }
+    fn f2(ref a: i32);
+    // { dg-error "pattern not allowed in function without body .E0642." "" { 
target *-*-* } .+1 }
+    fn f3(a @ _: i32);
+    // { dg-error "pattern not allowed in function without body .E0642." "" { 
target *-*-* } .+1 }
+    fn f4((a,): i32);
+    // { dg-error "pattern not allowed in function without body .E0642." "" { 
target *-*-* } .+1 }
+    fn f5((a): i32);
+
+    fn f6(_: i32);
+}