Remove support for GCC 7 and 8

- remove GCC 8.1 from Windows workflow - remove GCC 7.5 and GCC 8.4 from Ubuntu/MacOS workflow - remove GCC workaround from stdlib_string_type - move GCC <9 from supported to failing compilers - create error in CMake for too old GCC version

.github/workflows/CI.yml

@@ -21,7 +21,7 @@ jobs:
  fail-fast: false
  matrix:
  os: [ubuntu-latest, macos-latest]
- gcc_v: [7, 8, 9, 10, 11] # Version of GFortran we want to use.
+ gcc_v: [9, 10, 11] # Version of GFortran we want to use.
  env:
  FC: gfortran-${{ matrix.gcc_v }}
  GCC_V: ${{ matrix.gcc_v }}

.github/workflows/ci_windows.yml

@@ -7,41 +7,6 @@ env:
  CTEST_TIME_TIMEOUT: "5" # some failures hang forever
 
 jobs:
- Build:
- runs-on: windows-latest
- strategy:
- fail-fast: false
-
- steps:
- - uses: actions/checkout@v1
-
- - name: Install fypp
- run: pip install fypp
-
- - run: cmake -G "MinGW Makefiles" -DCMAKE_SH="CMAKE_SH-NOTFOUND" -Wdev -B build -DCMAKE_BUILD_TYPE=Debug -DCMAKE_Fortran_FLAGS_DEBUG="-Wall -Wextra -Wimplicit-interface -fPIC -g -fcheck=all -fbacktrace" -DCMAKE_MAXIMUM_RANK=4
-
- env:
- FC: gfortran
- CC: gcc
- CXX: g++
-
- - name: CMake build
- run: cmake --build build --parallel
-
- - name: catch build fail
- run: cmake --build build --verbose --parallel 1
- if: failure()
-
- - name: CTest
- run: ctest --output-on-failure --parallel -V -LE quadruple_precision
- working-directory: build
-
- - uses: actions/upload-artifact@v1
- if: failure()
- with:
- name: WindowsCMakeTestlog
- path: build/Testing/Temporary/LastTest.log
-
  msys2-build:
  runs-on: windows-latest
  strategy:

CMakeLists.txt

@@ -16,6 +16,9 @@ add_subdirectory(config)
 
 # --- compiler options
 if(CMAKE_Fortran_COMPILER_ID STREQUAL GNU)
+ if(CMAKE_Fortran_COMPILER_VERSION VERSION_LESS 9.0)
+ message(FATAL_ERROR "GCC Version 9 or newer required")
+ endif()
  add_compile_options(-fimplicit-none)
  add_compile_options(-ffree-line-length-132)
  add_compile_options(-Wall)
@@ -27,11 +30,7 @@ if(CMAKE_Fortran_COMPILER_ID STREQUAL GNU)
  if(CMAKE_Fortran_COMPILER_VERSION VERSION_LESS 11.0)
  add_compile_options(-pedantic-errors)
  endif()
- if(CMAKE_Fortran_COMPILER_VERSION VERSION_GREATER_EQUAL 8.0)
- add_compile_options(-std=f2018)
- else()
- add_compile_options(-std=f2008ts)
- endif()
+ add_compile_options(-std=f2018)
 elseif(CMAKE_Fortran_COMPILER_ID STREQUAL Intel)
  add_compile_options(-warn declarations,general,usage,interfaces,unused)
  if(CMAKE_Fortran_COMPILER_VERSION VERSION_LESS 18.0)

README.md

@@ -87,9 +87,8 @@ The following combinations are tested on the default branch of stdlib:
 
 Name | Version | Platform | Architecture
 --- | --- | --- | ---
-GCC Fortran | 7, 8, 9, 10, 11 | Ubuntu 20.04 | x86_64
-GCC Fortran | 7, 8, 9, 10, 11 | MacOS Catalina 10.15 | x86_64
-GCC Fortran | 8 | Windows Server 2019 | x86_64
+GCC Fortran | 9, 10, 11 | Ubuntu 20.04 | x86_64
+GCC Fortran | 9, 10, 11 | MacOS Catalina 10.15 | x86_64
 GCC Fortran (MSYS) | 10 | Windows Server 2019 | x86_64
 GCC Fortran (MinGW) | 10 | Windows Server 2019 | x86_64, i686
 Intel oneAPI classic | 2021.1 | Ubuntu 20.04 | x86_64
@@ -106,7 +105,7 @@ A list of tested compilers which are currently not working and the respective is
 
 Name | Version | Platform | Architecture | Status
 --- | --- | --- | --- | ---
-GCC Fortran | 7.4 | Windows 10 | i686 | [#296](https://github.com/fortran-lang/stdlib/issues/296)
+GCC Fortran | <9 | any | any | [#430](https://github.com/fortran-lang/stdlib/pull/430)
 NVIDIA HPC SDK | 20.7, 20.9, 20.11 | Manjaro Linux 20 | x86_64 | [#107](https://github.com/fortran-lang/stdlib/issues/107)
 NAG | 7.0 | RHEL | x86_64 | [#108](https://github.com/fortran-lang/stdlib/issues/108)
 Intel Parallel Studio XE | 16, 17, 18 | OpenSUSE | x86_64 | failed to compile

src/stdlib_string_type.fypp

@@ -447,9 +447,7 @@ contains
  !> Return the character sequence represented by the string.
  pure function char_string(string) result(character_string)
  type(string_type), intent(in) :: string
- ! GCC 8 and older cannot evaluate pure derived type procedures here
- !character(len=len(string)) :: character_string
- character(len=:), allocatable :: character_string
+ character(len=len(string)) :: character_string
 
  character_string = maybe(string)
 
@@ -1241,9 +1239,7 @@ contains
  !> Safely return the character sequences represented by the string
  pure function maybe(string) result(maybe_string)
  type(string_type), intent(in) :: string
- ! GCC 8 and older cannot evaluate pure derived type procedures here
- !character(len=len(string)) :: maybe_string
- character(len=:), allocatable :: maybe_string
+ character(len=len(string)) :: maybe_string
  if (allocated(string%raw)) then
  maybe_string = string%raw
  else