From f75555136b026cd65c49169936c4075f6a07514a Mon Sep 17 00:00:00 2001
From: Massimiliano Culpo <massimiliano.culpo@gmail.com>
Date: Wed, 5 Feb 2025 11:55:30 +0100
Subject: [PATCH] No flag propagation when compilers are different

Flag propagation is not activated on nodes with
a compiler that is different from the propagation
source
---
 lib/spack/spack/solver/concretize.lp               | 13 ++++++++-----
 lib/spack/spack/test/concretization/flag_mixing.py | 13 +++++++++----
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/lib/spack/spack/solver/concretize.lp b/lib/spack/spack/solver/concretize.lp
index 85e257443bd..7e9052af779 100644
--- a/lib/spack/spack/solver/concretize.lp
+++ b/lib/spack/spack/solver/concretize.lp
@@ -1244,15 +1244,18 @@ error(100, "Cannot propagate the variant '{0}' from the package: {1} because pac
 
 % A propagated flag implies:
 % 1. The same flag type is not set on this node
-% 2. This node has the same compiler as the propagation source
+% 2. This node has the same compilers as the propagation source
+
+node_compiler(node(X, Package), node(Y, Compiler)) :-
+     attr("virtual_on_edge", node(X, Package), node(Y, Compiler), Language),
+     attr("version", node(Y, Compiler), Version),
+     compiler(Compiler), language(Language).
 
 propagated_flag(node(PackageID, Package), node_flag(FlagType, Flag, FlagGroup, Source), SourceNode) :-
   propagate(node(PackageID, Package), node_flag(FlagType, Flag, FlagGroup, Source), _),
   not attr("node_flag_set", node(PackageID, Package), node_flag(FlagType, _, _, "literal")),
-  % FIXME (compiler as nodes): do we need to match the compiler?
-  % Same compiler as propagation source
-  % node_compiler(node(PackageID, Package), CompilerID),
-  % node_compiler(SourceNode, CompilerID),
+  % Same compilers as propagation source
+  node_compiler(node(PackageID, Package), CompilerNode) : node_compiler(SourceNode, CompilerNode);
   attr("propagate", SourceNode, node_flag(FlagType, Flag, FlagGroup, Source), _),
   node(PackageID, Package) != SourceNode,
   not runtime(Package).
diff --git a/lib/spack/spack/test/concretization/flag_mixing.py b/lib/spack/spack/test/concretization/flag_mixing.py
index 2b6e0dd9744..2859a7dd715 100644
--- a/lib/spack/spack/test/concretization/flag_mixing.py
+++ b/lib/spack/spack/test/concretization/flag_mixing.py
@@ -198,10 +198,6 @@ def test_propagate_and_compiler_cfg(concretize_scope, test_repo):
     assert root_spec["y"].satisfies("cflags='-f1 -f2'")
 
 
-# Note: setting flags on a dependency overrides propagation, which
-# is tested in test/concretize.py:test_compiler_flag_propagation
-
-
 def test_propagate_and_pkg_dep(concretize_scope, test_repo):
     root_spec1 = spack.concretize.concretize_one("x ~activatemultiflag cflags=='-f1'")
     assert root_spec1["y"].satisfies("cflags='-f1 -d1'")
@@ -275,3 +271,12 @@ def test_diamond_dep_flag_mixing(concretize_scope, test_repo):
     spec1 = root_spec1["y"]
     assert spec1.satisfies('cflags="-c1 -c2 -d1 -d2 -e1 -e2"')
     assert spec1.compiler_flags["cflags"] == "-c1 -c2 -e1 -e2 -d1 -d2".split()
+
+
+def test_flag_injection_different_compilers(mock_packages, mutable_config):
+    """Tests that flag propagation is not activated on nodes with a compiler that is different
+    from the propagation source.
+    """
+    s = spack.concretize.concretize_one('mpileaks %gcc cflags=="-O2" ^callpath %llvm')
+    assert s.satisfies('cflags="-O2"') and s["c"].name == "gcc"
+    assert not s["callpath"].satisfies('cflags="-O2"') and s["callpath"]["c"].name == "llvm"