ci: Replace exec-with-shell wrapper with "plain bash"

Also, promote defaults.run.shell from inside only the primary jobs to the top level. The src/ci/exec-with-shell.py wrapper script was formerly used to change out the shell mid-job by intercepting a CI_OVERRIDE_SHELL environment variable. Now, instead, we just set `bash` as the global default across all jobs, and we also delete the exec-with-shell.py script. Signed-off-by: Kristofer Rye <kristofer.rye@gmail.com>

Author: rye

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ name: CI
  - "**"
 defaults:
  run:
- shell: "python src/ci/exec-with-shell.py {0}"
+ shell: bash
 jobs:
  pr:
  name: PR
@@ -51,9 +51,6 @@ jobs:
  os: ubuntu-latest-xl
  timeout-minutes: 600
  runs-on: "${{ matrix.os }}"
- defaults:
- run:
- shell: bash
  steps:
  - name: disable git crlf conversion
  run: git config --global core.autocrlf false
@@ -153,9 +150,6 @@ jobs:
  env: {}
  timeout-minutes: 600
  runs-on: "${{ matrix.os }}"
- defaults:
- run:
- shell: bash
  steps:
  - name: disable git crlf conversion
  run: git config --global core.autocrlf false
@@ -473,9 +467,6 @@ jobs:
  os: windows-latest-xl
  timeout-minutes: 600
  runs-on: "${{ matrix.os }}"
- defaults:
- run:
- shell: bash
  steps:
  - name: disable git crlf conversion
  run: git config --global core.autocrlf false
@@ -601,9 +592,6 @@ jobs:
  os: macos-latest
  timeout-minutes: 600
  runs-on: "${{ matrix.os }}"
- defaults:
- run:
- shell: bash
  steps:
  - name: disable git crlf conversion
  run: git config --global core.autocrlf false

src/ci/exec-with-shell.py

@@ -75,9 +75,6 @@ x--expand-yaml-anchors--remove:
  - &base-ci-job
  timeout-minutes: 600
  runs-on: "${{ matrix.os }}"
- defaults:
- run:
- shell: bash
  env: *shared-ci-variables
  steps:
  - name: disable git crlf conversion
@@ -233,18 +230,10 @@ on:
 
 defaults:
  run:
- # While on Linux and macOS builders it just forwards the arguments to the
- # system bash, this wrapper allows switching from the host's bash.exe to
- # the one we install along with MSYS2 mid-build on Windows.
- #
- # Once the step to install MSYS2 is executed, the CI_OVERRIDE_SHELL
- # environment variable is set pointing to our MSYS2's bash.exe. From that
- # moment the host's bash.exe will not be called anymore.
- #
- # This is needed because we can't launch our own bash.exe from the host
- # bash.exe, as that would load two different cygwin1.dll in memory, causing
- # "cygwin heap mismatch" errors.
- shell: python src/ci/exec-with-shell.py {0}
+ # On Linux, macOS, and Windows, use the system-provided bash as the default
+ # shell. (This should only make a difference on Windows, where the default
+ # shell is PowerShell.)
+ shell: bash
 
 jobs:
  pr: