cmake: do not install shell completions when `BUILD_CURL_EXE=OFF`

Follow-up to 74542c1f4bfea75f92562075370fd839891cc440 #21459

Closes #21460

scripts/CMakeLists.txt

diff --git a/scripts/CMakeLists.txt b/scripts/CMakeLists.txt
index 54bb814..f0617e5 100644
--- a/scripts/CMakeLists.txt
+++ b/scripts/CMakeLists.txt
@@ -22,57 +22,59 @@
 #
 ###########################################################################
 
-option(CURL_COMPLETION_FISH "Install fish completions" OFF)
-option(CURL_COMPLETION_ZSH "Install zsh completions" OFF)
+if(BUILD_CURL_EXE)
+  option(CURL_COMPLETION_FISH "Install fish completions" OFF)
+  option(CURL_COMPLETION_ZSH "Install zsh completions" OFF)
 
-if(CURL_COMPLETION_FISH OR
-   CURL_COMPLETION_ZSH)
-  if(Perl_FOUND)
-    if(CURL_COMPLETION_FISH)
-      set(_completion_fish "${CMAKE_CURRENT_BINARY_DIR}/curl.fish")
-      add_custom_command(OUTPUT "${_completion_fish}"
-        COMMAND "${PERL_EXECUTABLE}" "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
-          --opts-dir "${PROJECT_SOURCE_DIR}/docs/cmdline-opts" --shell fish > "${_completion_fish}"
-        DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
-        VERBATIM
-      )
-      add_custom_target("curl-completion-fish" ALL DEPENDS "${_completion_fish}")
-    endif()
-
-    if(CURL_COMPLETION_ZSH)
-      set(_completion_zsh "${CMAKE_CURRENT_BINARY_DIR}/_curl")
-      add_custom_command(OUTPUT "${_completion_zsh}"
-        COMMAND "${PERL_EXECUTABLE}" "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
-          --opts-dir "${PROJECT_SOURCE_DIR}/docs/cmdline-opts" --shell zsh > "${_completion_zsh}"
-        DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
-        VERBATIM
-      )
-      add_custom_target("curl-completion-zsh" ALL DEPENDS "${_completion_zsh}")
-    endif()
-
-    if(NOT CURL_DISABLE_INSTALL)
+  if(CURL_COMPLETION_FISH OR
+     CURL_COMPLETION_ZSH)
+    if(Perl_FOUND)
       if(CURL_COMPLETION_FISH)
-        if(NOT CURL_COMPLETION_FISH_DIR AND NOT CMAKE_CROSSCOMPILING AND NOT DEFINED CMAKE_INSTALL_PREFIX)
-          find_package(PkgConfig QUIET)
-          pkg_get_variable(CURL_COMPLETION_FISH_DIR "fish" "completionsdir")
-        endif()
-        if(NOT CURL_COMPLETION_FISH_DIR AND CMAKE_INSTALL_DATAROOTDIR)
-          set(CURL_COMPLETION_FISH_DIR "${CMAKE_INSTALL_DATAROOTDIR}/fish/vendor_completions.d")
-        endif()
-        if(CURL_COMPLETION_FISH_DIR)
-          install(FILES "${_completion_fish}" DESTINATION "${CURL_COMPLETION_FISH_DIR}")
-        endif()
+        set(_completion_fish "${CMAKE_CURRENT_BINARY_DIR}/curl.fish")
+        add_custom_command(OUTPUT "${_completion_fish}"
+          COMMAND "${PERL_EXECUTABLE}" "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
+            --opts-dir "${PROJECT_SOURCE_DIR}/docs/cmdline-opts" --shell fish > "${_completion_fish}"
+          DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
+          VERBATIM
+        )
+        add_custom_target("curl-completion-fish" ALL DEPENDS "${_completion_fish}")
       endif()
+
       if(CURL_COMPLETION_ZSH)
-        if(NOT CURL_COMPLETION_ZSH_DIR AND CMAKE_INSTALL_DATAROOTDIR)
-          set(CURL_COMPLETION_ZSH_DIR "${CMAKE_INSTALL_DATAROOTDIR}/zsh/site-functions")
+        set(_completion_zsh "${CMAKE_CURRENT_BINARY_DIR}/_curl")
+        add_custom_command(OUTPUT "${_completion_zsh}"
+          COMMAND "${PERL_EXECUTABLE}" "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
+            --opts-dir "${PROJECT_SOURCE_DIR}/docs/cmdline-opts" --shell zsh > "${_completion_zsh}"
+          DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/completion.pl"
+          VERBATIM
+        )
+        add_custom_target("curl-completion-zsh" ALL DEPENDS "${_completion_zsh}")
+      endif()
+
+      if(NOT CURL_DISABLE_INSTALL)
+        if(CURL_COMPLETION_FISH)
+          if(NOT CURL_COMPLETION_FISH_DIR AND NOT CMAKE_CROSSCOMPILING AND NOT DEFINED CMAKE_INSTALL_PREFIX)
+            find_package(PkgConfig QUIET)
+            pkg_get_variable(CURL_COMPLETION_FISH_DIR "fish" "completionsdir")
+          endif()
+          if(NOT CURL_COMPLETION_FISH_DIR AND CMAKE_INSTALL_DATAROOTDIR)
+            set(CURL_COMPLETION_FISH_DIR "${CMAKE_INSTALL_DATAROOTDIR}/fish/vendor_completions.d")
+          endif()
+          if(CURL_COMPLETION_FISH_DIR)
+            install(FILES "${_completion_fish}" DESTINATION "${CURL_COMPLETION_FISH_DIR}")
+          endif()
         endif()
-        if(CURL_COMPLETION_ZSH_DIR)
-          install(FILES "${_completion_zsh}" DESTINATION "${CURL_COMPLETION_ZSH_DIR}")
+        if(CURL_COMPLETION_ZSH)
+          if(NOT CURL_COMPLETION_ZSH_DIR AND CMAKE_INSTALL_DATAROOTDIR)
+            set(CURL_COMPLETION_ZSH_DIR "${CMAKE_INSTALL_DATAROOTDIR}/zsh/site-functions")
+          endif()
+          if(CURL_COMPLETION_ZSH_DIR)
+            install(FILES "${_completion_zsh}" DESTINATION "${CURL_COMPLETION_ZSH_DIR}")
+          endif()
         endif()
       endif()
+    else()
+      message(WARNING "No perl: cannot generate completion script")
     endif()
-  else()
-    message(WARNING "No perl: cannot generate completion script")
   endif()
 endif()