Add windows latest and gcc 8 builds to azure (#446)

* add windows latest and gcc 8 builds to azure

* try adding pr trigger

* try adding something specific for gcc 8

* use interface instead of public

* try C++17 on clang 8

* update the readme with some additional notes about gcc 8

* fix some incorrect doxygen comment formatting

* try using the glibcxx_release value

* debug some code paths to make sure macros are working

* Update readme and fix formatting.

* update formatting for Validators

README.md

@@ -151,6 +151,21 @@ make
 GTEST_COLOR=1 CTEST_OUTPUT_ON_FAILURE=1 make test
 ```
 
+<details><summary>Note: Special instructions for GCC 8</summary><p>
+
+If you are using GCC 8 and using it in C++17 mode with CLI11.  CLI11 makes use of the `<filesystem>` header if available, but specifically for this compiler, the `filesystem` library is separate from the standard library and needs to be linked separately. So it is available but CLI11 doesn't use it by default.
+
+Specifically `libstdc++fs` needs to be added to the linking list and `CLI11_HAS_FILESYSTEM=1` has to be defined.  Then the filesystem variant of the Validators could be used on GCC 8.  GCC 9+ does not have this issue so the `<filesystem>` is used by default.
+
+There may also be other cases where a specific library needs to be linked.
+
+Defining `CLI11_HAS_FILESYSTEM=0`  which will remove the usage and hence any linking issue.
+
+In some cases certain clang compilations may require linking against `libc++fs`.  These situations have not been encountered so the specific situations requiring them are unknown yet.
+
+</p></details>
+</br>
+
 ## Usage
 
 ### Adding options

azure-pipelines.yml

@@ -6,6 +6,9 @@
 trigger:
 - master
 
+pr:
+- master
+
 variables:
   cli11.single: ON
   cli11.std: 14
@@ -57,6 +60,9 @@ jobs:
       Windows11:
         vmImage: 'vs2017-win2016'
         cli11.std: 11
+      Windowslatest:
+        vmImage: 'windows-2019'
+        cli11.std: 17
   pool:
     vmImage: $(vmImage)
   steps:
@@ -89,6 +95,9 @@ jobs:
       gcc9:
         containerImage: gcc:9
         cli11.std: 17
+      gcc8:
+        containerImage: gcc:8
+        cli11.std: 17
       gcc4.8:
         containerImage: gcc:4.8
         cli11.std: 11
@@ -100,6 +109,10 @@ jobs:
         containerImage: silkeh/clang:8
         cli11.std: 14
         cli11.options: -DCLI11_FORCE_LIBCXX=ON
+      clang8_17:
+        containerImage: silkeh/clang:8
+        cli11.std: 17
+        cli11.options: -DCLI11_FORCE_LIBCXX=ON
   container: $[ variables['containerImage'] ]
   steps:
     - template: .ci/azure-cmake.yml

include/CLI/FormatterFwd.hpp

@@ -24,9 +24,9 @@ class App;
 /// the second argument.
 
 enum class AppFormatMode {
-    Normal,  //< The normal, detailed help
+    Normal,  ///< The normal, detailed help
-    All,     //< A fully expanded help
+    All,     ///< A fully expanded help
-    Sub,     //< Used when printed as part of expanded subcommand
+    Sub,     ///< Used when printed as part of expanded subcommand
 };
 
 /// This is the minimum requirements to run a formatter.

include/CLI/Validators.hpp

@@ -33,7 +33,14 @@
 #else
 #include <filesystem>
 #if defined __cpp_lib_filesystem && __cpp_lib_filesystem >= 201703
+#if defined _GLIBCXX_RELEASE && _GLIBCXX_RELEASE >= 9
 #define CLI11_HAS_FILESYSTEM 1
+#elif defined(__GLIBCXX__)
+// if we are using gcc and Version <9 default to no filesystem
+#define CLI11_HAS_FILESYSTEM 0
+#else
+#define CLI11_HAS_FILESYSTEM 1
+#endif
 #else
 #define CLI11_HAS_FILESYSTEM 0
 #endif