From 870da744b736aba9f761c3ad2e78a58cb31c0c57 Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Sat, 16 Jul 2022 11:15:26 -0700
Subject: [PATCH 1/3] Add `-DCMAKE_VERBOSE_MAKEFILE:BOOL=ON` to `gcc` job (for
 debugging C++20 vs C++17 mismatch).

---
 .github/workflows/ci.yml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 412282a4f2..7ef5e3a87d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -465,6 +465,7 @@ jobs:
       shell: bash
       run: >
         cmake -S . -B build
+        -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DCMAKE_CXX_STANDARD=${{ matrix.std }}

From eb264e7a9a5bdc2fa92ced147b1e1e89a5b8b133 Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Sat, 16 Jul 2022 11:59:42 -0700
Subject: [PATCH 2/3] Try `std: 2a` for GCC 10

---
 .github/workflows/ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7ef5e3a87d..08c8d4966a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -444,7 +444,7 @@ jobs:
           - 11
         include:
           - gcc: 10
-            std: 20
+            std: 2a
 
     name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std }}• x64"
     container: "gcc:${{ matrix.gcc }}"

From 8735e8e7abae489d02a356a9d779a2d7adc0ed7e Mon Sep 17 00:00:00 2001
From: "Ralf W. Grosse-Kunstleve" <rwgk@google.com>
Date: Mon, 18 Jul 2022 07:45:55 -0700
Subject: [PATCH 3/3] Distinguish cmake_cxx_standard & std_passed_to_compiler,
 to make it more obvious what is actually being tested, and why PYBIND11_CPP20
 is not defined.

---
 .github/workflows/ci.yml | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 08c8d4966a..d1b1cf598c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -440,13 +440,16 @@ jobs:
         gcc:
           - 7
           - latest
-        std:
+        cmake_cxx_standard:
+          - 11
+        std_passed_to_compiler:
           - 11
         include:
           - gcc: 10
-            std: 2a
+            cmake_cxx_standard: 20
+            std_passed_to_compiler: 2a # pybind11 defines PYBIND11_CPP17 but not PYBIND11_CPP20
 
-    name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std }}• x64"
+    name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std_passed_to_compiler }} • x64"
     container: "gcc:${{ matrix.gcc }}"
 
     steps:
@@ -468,7 +471,7 @@ jobs:
         -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
-        -DCMAKE_CXX_STANDARD=${{ matrix.std }}
+        -DCMAKE_CXX_STANDARD=${{ matrix.cmake_cxx_standard }}
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Build