[FEATURE] Add sharg-parser submodule.

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "cereal"]
 	path = submodules/cereal
 	url = https://github.com/USCiLab/cereal
+[submodule "submodules/sharg-parser"]
+	path = submodules/sharg-parser
+	url = https://github.com/seqan/sharg-parser.git

build_system/seqan3-config.cmake

@@ -26,6 +26,7 @@
 #
 # SeqAn has the following optional dependencies:
 #
+#   Sharg     -- Argument Parsing
 #   ZLIB      -- zlib compression library
 #   BZip2     -- libbz2 compression library
 #   Cereal    -- Serialisation library
@@ -36,6 +37,7 @@
 #
 # If you wish to require the presence of ZLIB or BZip2, just check for the module before
 # finding SeqAn3, e.g. "find_package (ZLIB REQUIRED)".
+# If you wish to require the presence of SHARG, you may define SEQAN3_SHARG.
 # If you wish to require the presence of CEREAL, you may define SEQAN3_CEREAL.
 # If you wish to require the presence of LEMON, you may define SEQAN3_LEMON.
 #
@@ -168,6 +170,25 @@ set (CMAKE_REQUIRED_FLAGS ${CMAKE_CXX_FLAGS})
 # Force-deactivate optional dependencies
 # ----------------------------------------------------------------------------
 
+# Sharg is auto-detected by default, i.e. used if found, not used if not found.
+# You can optionally set a hard requirement so a build fails without Sharg,
+# or you can force-disable Sharg even if present on the system.
+option (SEQAN3_SHARG "Require Sharg and fail if not present." OFF)
+option (SEQAN3_NO_SHARG "Don't use Sharg, even if present." OFF)
+
+if (SEQAN3_SHARG AND SEQAN3_NO_SHARG)
+    # this is always a user error, therefore we always error-out, even if SeqAn is not required
+    message (FATAL_ERROR "You may not specify SEQAN3_SHARG and SEQAN3_NO_SHARG at the same time.\n\
+                          You can specify neither (use auto-detection), or specify either to force on/off.")
+    return ()
+endif ()
+
+if (SEQAN3_SHARG)
+    set (SEQAN3_DEFINITIONS ${SEQAN3_DEFINITIONS} "-DSEQAN3_WITH_SHARG=1")
+elseif (SEQAN3_NO_SHARG)
+    set (SEQAN3_DEFINITIONS ${SEQAN3_DEFINITIONS} "-DSEQAN3_WITH_SHARG=0")
+endif ()
+
 # Cereal is auto-detected by default, i.e. used if found, not used if not found.
 # You can optionally set a hard requirement so a build fails without cereal,
 # or you can force-disable cereal even if present on the system.
@@ -320,6 +341,28 @@ else ()
         "The SDSL library is required, but wasn't found. Get it from https://github.com/xxsds/sdsl-lite")
 endif ()
 
+# ----------------------------------------------------------------------------
+# Sharg dependency is optional, but may set as required
+# ----------------------------------------------------------------------------
+
+if (NOT SEQAN3_NO_SHARG)
+    check_include_file_cxx (sharg/version.hpp _SEQAN3_HAVE_SHARG)
+
+    if (_SEQAN3_HAVE_SHARG)
+        if (SEQAN3_SHARG)
+            seqan3_config_print ("Required dependency:        Sharg found.")
+        else ()
+            seqan3_config_print ("Optional dependency:        Sharg found.")
+        endif ()
+    else ()
+        if (SEQAN3_SHARG)
+            seqan3_config_error ("The (optional) Sharg library was marked as required, but wasn't found.")
+        else ()
+            seqan3_config_print ("Optional dependency:        Sharg not found.")
+        endif ()
+    endif ()
+endif ()
+
 # ----------------------------------------------------------------------------
 # Cereal dependency is optional, but may set as required
 # ----------------------------------------------------------------------------