[INFRA] Drop gcc9

README.md

@@ -66,7 +66,7 @@ Please see the [online documentation](https://docs.seqan.de/seqan/3-master-user/
 
 |                   | requirement                                          | version  | comment                                     |
 |-------------------|------------------------------------------------------|----------|---------------------------------------------|
-|**compiler**       | [GCC](https://gcc.gnu.org)                           | ≥ 7      | no other compiler is currently supported!   |
+|**compiler**       | [GCC](https://gcc.gnu.org)                           | ≥ 10     | no other compiler is currently supported!   |
 |**build system**   | [CMake](https://cmake.org)                           | ≥ 3.4    | optional, but recommended                   |
 |**required libs**  | [SDSL](https://github.com/xxsds/sdsl-lite)           | ≥ 3      |                                             |
 |                   | [Range-V3](https://github.com/ericniebler/range-v3)  | ≥ 0.11.0 |                                             |
@@ -86,18 +86,18 @@ Quick-Setup without CMake:
   * Clone the repository with submodules: `git clone --recurse-submodules https://github.com/seqan/seqan3.git`
   * Add the following to your compiler invocation:
     * the include directories of SeqAn and its dependencies
-    * C++17 mode with concepts support
+    * C++20 mode
     * Macros indicating the presence of zlib and bzip2 (set only if actually available in your paths!)
   * The command could look like this:
 ```sh
-g++-7 -O3 -DNDEBUG -Wall -Wextra                                \
-    -std=c++17 -fconcepts                                       \
+g++-11 -O3 -DNDEBUG -Wall -Wextra                               \
+    -std=c++20                                                  \
     -I       /path/to/seqan3/include                            \
     -isystem /path/to/seqan3/submodules/range-v3/include        \
     -isystem /path/to/seqan3/submodules/sdsl-lite/include       \
     -isystem /path/to/seqan3/submodules/cereal/include          \
     -DSEQAN3_HAS_ZLIB=1 -DSEQAN3_HAS_BZIP2=1                    \
-    -lz -lbz2 -lstdc++fs -pthread                               \
+    -lz -lbz2 -pthread                                          \
   your_file.cpp
 ```
 

doc/tutorial/concepts/index.md

@@ -118,8 +118,6 @@ auto add(std::integral auto const v1, std::integral auto const v2)  // one const
 }
 ```
 
-\attention The terse syntax in this form is not yet available in GCC7, GCC8 and GCC9.
-
 Different constraints can be applied to different template parameters and a single template parameter can be constrained
 by multiple concepts.
 Syntaxes can also be combined:

include/seqan3/core/platform.hpp

@@ -36,35 +36,23 @@
 //  Compiler support
 // ============================================================================
 
-#if defined(__GNUC__) && (__GNUC__ == 7 || __GNUC__ == 8)
-#   error "SeqAn 3.1.x is the last version that supports GCC 7 and 8. Please upgrade your compiler or use 3.1.x."
+#if defined(__GNUC__) && (__GNUC__ == 7 || __GNUC__ == 8 || __GNUC__ == 9)
+#   error "SeqAn 3.1.x is the last version that supports GCC 7, 8, and 9. Please upgrade your compiler or use 3.1.x."
 #endif // defined(__GNUC__) && (__GNUC__ == 7 || __GNUC__ == 8)
 
 // ============================================================================
 //  C++ standard and features
 // ============================================================================
 
-#if SEQAN3_DOXYGEN_ONLY(1)0
-//!\brief This disables the warning you would get if you compile with `-std=c++17`.
-#define SEQAN3_DISABLE_CPP17_DIAGNOSTIC
-#endif // SEQAN3_DOXYGEN_ONLY(1)0
-
 // C++ standard [required]
 #ifdef __cplusplus
-#   if (__cplusplus < 201703)
-#       error "SeqAn3 requires C++20, make sure that you have set -std=c++2a (gcc9) or -std=c++20 (gcc10 and higher)."
-#   elif not defined(SEQAN3_DISABLE_CPP17_DIAGNOSTIC) && (__cplusplus >= 201703) && (__cplusplus < 201709)
-#      pragma GCC warning "SeqAn 3.1.x is the last version that supports C++17. Newer SeqAn versions, including this one, might not compile with -std=c++17. To disable this warning, use -std=c++2a (gcc9), -std=c++20 (gcc10 and higher), or -DSEQAN3_DISABLE_CPP17_DIAGNOSTIC."
+#   if (__cplusplus < 201709)
+#       error "SeqAn3 requires C++20, make sure that you have set -std=c++20."
 #   endif
 #else
 #   error "This is not a C++ compiler."
 #endif
 
-// C++ Concepts [required]
-#ifndef __cpp_concepts
-#   error "SeqAn3 requires C++ Concepts, either via -fconcepts (gcc9), or -std=c++20 (gcc10 and higher)."
-#endif
-
 #if __has_include(<version>)
 #   include <version>
 #endif

test/unit/alignment/matrix/detail/two_dimensional_matrix_test.cpp

@@ -28,7 +28,7 @@ using test_matrix_t = seqan3::detail::two_dimensional_matrix<score_t, allocator_
 template <typename score_type, seqan3::detail::matrix_major_order order = seqan3::detail::matrix_major_order::row>
 std::vector<score_type, std::allocator<score_type>> create_matrix_storage()
 {
-    // this is a small hack to allow simd types in an initialiser list on gcc 7 and gcc 10;
+    // this is a small hack to allow simd types in an initialiser list on gcc 10;
     using storage_t = std::array<score_type, 12>;
 
     // note: we represent the same matrix in one case with a row-wise data layout and in the other case with a