[gcc r15-6997] c++/modules: Propagate FNDECL_USED_AUTO when propagating deduced return types [PR118049]

[Nathaniel Shead via Gcc-cvs]

https://gcc.gnu.org/g:f054c36c4fcb693e04411dc691ef4172479143d6

commit r15-6997-gf054c36c4fcb693e04411dc691ef4172479143d6
Author: Nathaniel Shead <nathanielosh...@gmail.com>
Date:   Fri Jan 17 21:29:08 2025 +1100

    c++/modules: Propagate FNDECL_USED_AUTO when propagating deduced return 
types [PR118049]
    
    In the linked testcase, we're erroring because the declared return types
    of the functions do not appear to match.  This is because when merging
    the deduced return types for 'foo' in 'auto-5_b.C', we overwrote the
    return type for the declaration with the deduced return type from
    'auto-5_a.C' but neglected to track that we were originally declared
    with 'auto'.
    
    As a drive-by improvement to QOI, also add checks for if the deduced
    return types do not match; this is currently useful because we do not
    check the equivalence of the bodies of functions yet.
    
            PR c++/118049
    
    gcc/cp/ChangeLog:
    
            * module.cc (trees_in::is_matching_decl): Propagate
            FNDECL_USED_AUTO as well.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/modules/auto-5_a.C: New test.
            * g++.dg/modules/auto-5_b.C: New test.
            * g++.dg/modules/auto-5_c.C: New test.
            * g++.dg/modules/auto-6_a.H: New test.
            * g++.dg/modules/auto-6_b.C: New test.
    
    Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com>

Diff:
---
 gcc/cp/module.cc                        |  5 +++++
 gcc/testsuite/g++.dg/modules/auto-5_a.C | 10 ++++++++++
 gcc/testsuite/g++.dg/modules/auto-5_b.C | 14 ++++++++++++++
 gcc/testsuite/g++.dg/modules/auto-5_c.C |  4 ++++
 gcc/testsuite/g++.dg/modules/auto-6_a.H |  5 +++++
 gcc/testsuite/g++.dg/modules/auto-6_b.C |  6 ++++++
 6 files changed, 44 insertions(+)

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 61116fe76693..6fe64bb538c2 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -11902,8 +11902,13 @@ trees_in::is_matching_decl (tree existing, tree decl, 
bool is_typedef)
        {
          dump (dumper::MERGE)
            && dump ("Propagating deduced return type to %N", existing);
+         FNDECL_USED_AUTO (e_inner) = true;
+         DECL_SAVED_AUTO_RETURN_TYPE (existing) = TREE_TYPE (e_type);
          TREE_TYPE (existing) = change_return_type (TREE_TYPE (d_type), 
e_type);
        }
+      else if (type_uses_auto (d_ret)
+              && !same_type_p (TREE_TYPE (d_type), TREE_TYPE (e_type)))
+       goto mismatch;
     }
   else if (is_typedef)
     {
diff --git a/gcc/testsuite/g++.dg/modules/auto-5_a.C 
b/gcc/testsuite/g++.dg/modules/auto-5_a.C
new file mode 100644
index 000000000000..fcab6f301e1c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-5_a.C
@@ -0,0 +1,10 @@
+// PR c++/118049
+// { dg-additional-options "-fmodules -Wno-global-module" }
+// { dg-module-cmi A }
+
+module;
+template <typename T> struct S {
+  auto foo() {}
+};
+export module A;
+template struct S<char>;
diff --git a/gcc/testsuite/g++.dg/modules/auto-5_b.C 
b/gcc/testsuite/g++.dg/modules/auto-5_b.C
new file mode 100644
index 000000000000..f75ed2d0f0cb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-5_b.C
@@ -0,0 +1,14 @@
+// PR c++/118049
+// { dg-additional-options "-fmodules -Wno-global-module" }
+// { dg-module-cmi B }
+
+module;
+template <typename T> struct S {
+  auto foo() {}
+};
+template struct S<char>;
+export module B;
+import A;
+template <typename> void x() {
+  S<char>{}.foo();
+}
diff --git a/gcc/testsuite/g++.dg/modules/auto-5_c.C 
b/gcc/testsuite/g++.dg/modules/auto-5_c.C
new file mode 100644
index 000000000000..f351c2b1ae45
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-5_c.C
@@ -0,0 +1,4 @@
+// PR c++/118049
+// { dg-additional-options "-fmodules -fno-module-lazy 
-fdump-lang-module-alias" }
+
+import B;
diff --git a/gcc/testsuite/g++.dg/modules/auto-6_a.H 
b/gcc/testsuite/g++.dg/modules/auto-6_a.H
new file mode 100644
index 000000000000..3ad08ab81ce4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-6_a.H
@@ -0,0 +1,5 @@
+// { dg-additional-options "-fmodule-header" }
+
+inline auto foo() {
+  return 1;
+}
diff --git a/gcc/testsuite/g++.dg/modules/auto-6_b.C 
b/gcc/testsuite/g++.dg/modules/auto-6_b.C
new file mode 100644
index 000000000000..aab7be4e5301
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/auto-6_b.C
@@ -0,0 +1,6 @@
+// { dg-additional-options "-fmodules-ts -fno-module-lazy" }
+
+inline auto foo() {  // { dg-error "conflicting" }
+  return 1.0;
+}
+import "auto-6_a.H";