Allow defining custom prefixes

In addition to the predefined prefixes 'gh', 'gl' and 'bb', allow
defining your own prefixes for, e.g. internal hosts.

README.md

@@ -81,6 +81,13 @@ CPMAddPackage("uri@version#tag")
 
 In the shorthand syntax if the URI is of the form `gh:user/name`, it is interpreted as GitHub URI and converted to `https://github.com/user/name.git`. If the URI is of the form `gl:user/name`, it is interpreted as a [GitLab](https://gitlab.com/explore/) URI and converted to `https://gitlab.com/user/name.git`. If the URI is of the form `bb:user/name`, it is interpreted as a [Bitbucket](https://bitbucket.org/) URI and converted to `https://bitbucket.org/user/name.git`. Otherwise the URI used verbatim as a git URL. All packages added using the shorthand syntax will be added using the [EXCLUDE_FROM_ALL](https://cmake.org/cmake/help/latest/prop_tgt/EXCLUDE_FROM_ALL.html) flag.
 
+In addition to the predefined prefixes, it is also possible to define custom prefixes, e.g.
+```cmake
+set(CPM_CUSTOM_PREFIXES c1:https://c1.example.com c2:https://c2.example.com)
+CPMAddPackage("c1:some/repo@1.2.3")
+CPMAddPackage("c2:another/repo#v1.2.3")
+```
+
 The single-argument syntax also works for URLs:
 
 ```cmake

cmake/CPM.cmake

@@ -339,7 +339,8 @@ endfunction()
 # to: GITHUB_REPOSITORY;foo/bar;VERSION;1.2.3
 function(cpm_parse_add_package_single_arg arg outArgs)
   # Look for a scheme
-  if("${arg}" MATCHES "^([a-zA-Z]+):(.+)$")
+
+  if("${arg}" MATCHES "^([a-zA-Z0-9]+):(.+)$")
     string(TOLOWER "${CMAKE_MATCH_1}" scheme)
     set(uri "${CMAKE_MATCH_2}")
 
@@ -353,19 +354,32 @@ function(cpm_parse_add_package_single_arg arg outArgs)
     elseif(scheme STREQUAL "bb")
       set(out "BITBUCKET_REPOSITORY;${uri}")
       set(packageType "git")
+    elseif(DEFINED CPM_CUSTOM_PREFIXES)
+      foreach(prefix ${CPM_CUSTOM_PREFIXES})
+        if("${prefix}" MATCHES "([^:]+):(.+)")
+          if(scheme STREQUAL "${CMAKE_MATCH_1}")
+            set(out "GIT_REPOSITORY;${uri};CUSTOM_REPOSITORY;${CMAKE_MATCH_2}")
+            set(packageType "git")
+            break()
+          endif()
+        endif()
+      endforeach()
+    endif()
+    if("${out}" STREQUAL "")
       # A CPM-specific scheme was not found. Looks like this is a generic URL so try to determine
       # type
-    elseif(arg MATCHES ".git/?(@|#|$)")
-      set(out "GIT_REPOSITORY;${arg}")
-      set(packageType "git")
-    else()
-      # Fall back to a URL
-      set(out "URL;${arg}")
-      set(packageType "archive")
-
-      # We could also check for SVN since FetchContent supports it, but SVN is so rare these days.
-      # We just won't bother with the additional complexity it will induce in this function. SVN is
-      # done by multi-arg
+      if(arg MATCHES ".git/?(@|#|$)")
+        set(out "GIT_REPOSITORY;${arg}")
+        set(packageType "git")
+      else()
+        # Fall back to a URL
+        set(out "URL;${arg}")
+        set(packageType "archive")
+
+        # We could also check for SVN since FetchContent supports it, but SVN is so rare these days.
+        # We just won't bother with the additional complexity it will induce in this function. SVN
+        # is done by multi-arg
+      endif()
     endif()
   else()
     if(arg MATCHES ".git/?(@|#|$)")
@@ -534,6 +548,7 @@ function(CPMAddPackage)
       GIT_SHALLOW
       EXCLUDE_FROM_ALL
       SOURCE_SUBDIR
+      CUSTOM_REPOSITORY
   )
 
   set(multiValueArgs URL OPTIONS)
@@ -560,6 +575,8 @@ function(CPMAddPackage)
     set(CPM_ARGS_GIT_REPOSITORY "https://gitlab.com/${CPM_ARGS_GITLAB_REPOSITORY}.git")
   elseif(DEFINED CPM_ARGS_BITBUCKET_REPOSITORY)
     set(CPM_ARGS_GIT_REPOSITORY "https://bitbucket.org/${CPM_ARGS_BITBUCKET_REPOSITORY}.git")
+  elseif(DEFINED CPM_ARGS_CUSTOM_REPOSITORY)
+    set(CPM_ARGS_GIT_REPOSITORY "${CPM_ARGS_CUSTOM_REPOSITORY}/${CPM_ARGS_GIT_REPOSITORY}.git")
   endif()
 
   if(DEFINED CPM_ARGS_GIT_REPOSITORY)

test/unit/parse_add_package_single_arg.cmake

@@ -36,6 +36,15 @@ assert_equal("BITBUCKET_REPOSITORY;foo/bar" "${args}")
 cpm_parse_add_package_single_arg("bb:foo/Bar" args)
 assert_equal("BITBUCKET_REPOSITORY;foo/Bar" "${args}")
 
+set(CPM_CUSTOM_PREFIXES c1:https://c1.example.com c2:https://c2.example.com/mirror)
+cpm_parse_add_package_single_arg("c1:foo/bar@13" args)
+assert_equal("GIT_REPOSITORY;foo/bar;VERSION;13;CUSTOM_REPOSITORY;https://c1.example.com" "${args}")
+
+cpm_parse_add_package_single_arg("c2:foo/Bar#bla" args)
+assert_equal(
+  "GIT_REPOSITORY;foo/Bar;GIT_TAG;bla;CUSTOM_REPOSITORY;https://c2.example.com/mirror" "${args}"
+)
+
 cpm_parse_add_package_single_arg("https://github.com/cpm-cmake/CPM.cmake.git@0.30.5" args)
 assert_equal("GIT_REPOSITORY;https://github.com/cpm-cmake/CPM.cmake.git;VERSION;0.30.5" "${args}")