Rollup merge of #112122 - compiler-errors:next-coherence, r=lcnr

Add `-Ztrait-solver=next-coherence`

Flag that conditionally uses the trait solver *only* during coherence, for more testing and/or eventual partial-migration onto the trait solver (in the medium- to long-term).

* This still uses the selection context in some of the coherence methods I think, so it's not "complete". Putting this up for review and/or for further work in-tree.
* I probably need to spend a bit more time making sure that we don't sneakily create any other infcx's during coherence that also need the new solver enabled.

r? `@lcnr`

2 files changed, 4 insertions, 0 deletions

diff --git a/src/tools/compiletest/src/common.rs b/src/tools/compiletest/src/common.rs
index f796c898731..96fe720630c 100644
--- a/src/tools/compiletest/src/common.rs
+++ b/src/tools/compiletest/src/common.rs
@@ -108,6 +108,7 @@ string_enum! {
         Polonius => "polonius",
         Chalk => "chalk",
         NextSolver => "next-solver",
+        NextSolverCoherence => "next-solver-coherence",
         SplitDwarf => "split-dwarf",
         SplitDwarfSingle => "split-dwarf-single",
     }
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 923b2e63f2e..6582b534488 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -2127,6 +2127,9 @@ impl<'test> TestCx<'test> {
             Some(CompareMode::NextSolver) => {
                 rustc.args(&["-Ztrait-solver=next"]);
             }
+            Some(CompareMode::NextSolverCoherence) => {
+                rustc.args(&["-Ztrait-solver=next-coherence"]);
+            }
             Some(CompareMode::SplitDwarf) if self.config.target.contains("windows") => {
                 rustc.args(&["-Csplit-debuginfo=unpacked", "-Zunstable-options"]);
             }