re-enable appveyor

.appveyor.yml

@@ -0,0 +1,43 @@
+version: 4.3.0.99.{build}
+
+image: Visual Studio 2015
+platform: x64
+configuration:  # a trick to construct a build matrix with multiple Python versions
+  - '3.8'
+
+# only build pull requests and
+# commits to 'master' or any branch starting with 'release'
+branches:
+  only:
+    - master
+    - /^release/
+
+environment:
+  matrix:
+    - COMPILER: MSVC
+      TASK: python
+    - COMPILER: MINGW
+      TASK: python
+
+clone_depth: 5
+
+install:
+  - git submodule update --init --recursive  # get `external_libs` folder
+  - set PATH=C:\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin;%PATH%
+  - set PYTHON_VERSION=%CONFIGURATION%
+  - set CONDA_ENV="test-env"
+  - ps: |
+      $env:MINICONDA = "C:\Miniconda3-x64"
+      $env:PATH = "$env:MINICONDA;$env:MINICONDA\Scripts;$env:PATH"
+      $env:BUILD_SOURCESDIRECTORY = "$env:APPVEYOR_BUILD_FOLDER"
+      $env:LGB_VER = (Get-Content $env:APPVEYOR_BUILD_FOLDER\VERSION.txt).trim()
+
+build: false
+
+test_script:
+  - conda config --remove channels defaults
+  - conda config --add channels nodefaults
+  - conda config --add channels conda-forge
+  - conda config --set channel_priority strict
+  - conda init powershell
+  - powershell.exe -ExecutionPolicy Bypass -File %APPVEYOR_BUILD_FOLDER%\.ci\test_windows.ps1

.ci/setup.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-set +x -e -E -o pipefail
+set -e -E -o pipefail
 
 if [[ $OS_NAME == "macos" ]]; then
     if  [[ $COMPILER == "clang" ]]; then

.ci/test.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-set +x -e -E -o pipefail
+set -e -E -o pipefail
 
 if [[ $OS_NAME == "macos" ]] && [[ $COMPILER == "gcc" ]]; then
     export CXX=g++-11