Rollup merge of #111167 - cuviper:type-decl-disubprogram, r=michaelwoerister

debuginfo: split method declaration and definition

When we're adding a method to a type DIE, we only want a DW_AT_declaration
there, because LLVM LTO can't unify type definitions when a child DIE is a
full subprogram definition. Now the subprogram definition gets added at the
CU level with a specification link back to the abstract declaration.

Both GCC and Clang write debuginfo this way for C++ class methods.

Fixes #109730.
Fixes #109934.

2 files changed, 21 insertions, 0 deletions

diff --git a/tests/run-make/issue-109934-lto-debuginfo/Makefile b/tests/run-make/issue-109934-lto-debuginfo/Makefile
new file mode 100644
index 00000000000..3b7a99d3dbc
--- /dev/null
+++ b/tests/run-make/issue-109934-lto-debuginfo/Makefile
@@ -0,0 +1,12 @@
+# ignore-cross-compile
+include ../tools.mk
+
+# With the upgrade to LLVM 16, this was getting:
+#
+#   error: Cannot represent a difference across sections
+#
+# The error stemmed from DI function definitions under type scopes, fixed by
+# only declaring in type scope and defining the subprogram elsewhere.
+
+all:
+	$(RUSTC) lib.rs --test -C lto=fat -C debuginfo=2 -C incremental=$(TMPDIR)/inc-fat
diff --git a/tests/run-make/issue-109934-lto-debuginfo/lib.rs b/tests/run-make/issue-109934-lto-debuginfo/lib.rs
new file mode 100644
index 00000000000..c405928bd18
--- /dev/null
+++ b/tests/run-make/issue-109934-lto-debuginfo/lib.rs
@@ -0,0 +1,9 @@
+extern crate alloc;
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn something_alloc() {
+        assert_eq!(Vec::<u32>::new(), Vec::<u32>::new());
+    }
+}