[gcc r10-9845] c++: lambda in DMI in class template [PR95870]

[gcc r10-9845] c++: lambda in DMI in class template [PR95870]

[Jason Merrill]

https://gcc.gnu.org/g:ff24ef677edee888012aaddeb0ec9bbe366b4f57

commit r10-9845-gff24ef677edee888012aaddeb0ec9bbe366b4f57
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Apr 5 11:34:48 2021 -0400

    c++: lambda in DMI in class template [PR95870]
    
    Here enclosing_instantiation_of was failing to find a match because otctx is
    struct S<T> and current_function_decl is S<int>::S(), so the latter has more
    function contexts, and we end up trying to compare S() to NULL_TREE.
    
    After spending a bit of time working on establishing the correspondence in
    this case (class <=> constructor), it occurred to me that we could just use
    DECL_SOURCE_LOCATION, which is unique for lambdas, since they cannot be
    redeclared.  Since we're so close to release, for now I'm only doing this
    for the case that was failing before.
    
    gcc/cp/ChangeLog:
    
            PR c++/95870
            * pt.c (enclosing_instantiation_of): Compare DECL_SOURCE_LOCATION if
            there is no enclosing non-lambda function.
    
    gcc/testsuite/ChangeLog:
    
            PR c++/95870
            * g++.dg/cpp0x/lambda/lambda-nsdmi10.C: New test.

Diff:
---
 gcc/cp/pt.c                                        | 13 +++++++++++++
 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nsdmi10.C | 12 ++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 986c8207a49..2026827e875 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -14269,6 +14269,19 @@ enclosing_instantiation_of (tree otctx)
 		  || instantiated_lambda_fn_p (tctx));
        tctx = decl_function_context (tctx))
     ++lambda_count;
+
+  if (!tctx)
+    {
+      /* Match using DECL_SOURCE_LOCATION, which is unique for all lambdas.
+
+	 For GCC 11 the above condition limits this to the previously failing
+	 case where all enclosing functions are lambdas (95870).  FIXME.  */
+      for (tree ofn = fn; ofn; ofn = decl_function_context (ofn))
+	if (DECL_SOURCE_LOCATION (ofn) == DECL_SOURCE_LOCATION (otctx))
+	  return ofn;
+      gcc_unreachable ();
+    }
+
   for (; fn; fn = decl_function_context (fn))
     {
       tree ofn = fn;
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nsdmi10.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nsdmi10.C
new file mode 100644
index 00000000000..810ed538719
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-nsdmi10.C
@@ -0,0 +1,12 @@
+// PR c++/95870
+// { dg-do compile { target c++11 } }
+
+template <typename> struct S {
+  S();
+  int b = []() -> int { enum E {}; return 1; }();
+};
+struct C : S<int> {
+  C();
+};
+template <typename T> S<T>::S() = default;
+C::C() {}