cmake: disable tests and man generation if perl/nroff not found

Fixes https://github.com/curl/curl/issues/1500
Reported-by: Jay Satiro

Fixes https://github.com/curl/curl/pull/1662
Assisted-by: Tom Seddon
Assisted-by: dpull@users.noreply.github.com
Assisted-by: elelel@users.noreply.github.com

Closes https://github.com/curl/curl/pull/1924

CMake/Macros.cmake

@@ -93,3 +93,32 @@ macro(CURL_INTERNAL_TEST_RUN CURL_TEST)
     endif(${CURL_TEST}_COMPILE AND NOT ${CURL_TEST})
   endif()
 endmacro(CURL_INTERNAL_TEST_RUN)
+
+macro(CURL_NROFF_CHECK)
+  find_program(NROFF NAMES gnroff nroff)
+  if(NROFF)
+    # Need a way to write to stdin, this will do
+    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/nroff-input.txt" "test")
+    # Tests for a valid nroff option to generate a manpage
+    foreach(_MANOPT "-man" "-mandoc")
+      execute_process(COMMAND "${NROFF}" ${_MANOPT}
+        OUTPUT_VARIABLE NROFF_MANOPT_OUTPUT
+        INPUT_FILE "${CMAKE_CURRENT_BINARY_DIR}/nroff-input.txt"
+        ERROR_QUIET)
+      # Save the option if it was valid
+      if(NROFF_MANOPT_OUTPUT)
+        message("Found *nroff option: -- ${_MANOPT}")
+        set(NROFF_MANOPT ${_MANOPT})
+        set(NROFF_USEFUL ON)
+        break()
+      endif()
+    endforeach()
+    # No need for the temporary file
+    file(REMOVE "${CMAKE_CURRENT_BINARY_DIR}/nroff-input.txt")
+    if(NOT NROFF_USEFUL)
+      message(WARNING "Found no *nroff option to get plaintext from man pages")
+    endif()
+  else()
+    message(WARNING "Found no *nroff program")
+  endif()
+endmacro(CURL_NROFF_CHECK)

CMakeLists.txt

@@ -203,38 +203,20 @@ if(ENABLE_IPV6 AND NOT WIN32)
   endif()
 endif()
 
-option(ENABLE_MANUAL "to provide the built-in manual" ON)
-unset(USE_MANUAL CACHE) # TODO: cache NROFF/NROFF_MANOPT/USE_MANUAL vars?
-if(ENABLE_MANUAL)
-  find_program(NROFF NAMES gnroff nroff)
-  if(NROFF)
-    # Need a way to write to stdin, this will do
-    file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/nroff-input.txt" "test")
-    # Tests for a valid nroff option to generate a manpage
-    foreach(_MANOPT "-man" "-mandoc")
-      execute_process(COMMAND "${NROFF}" ${_MANOPT}
-        OUTPUT_VARIABLE NROFF_MANOPT_OUTPUT
-        INPUT_FILE "${CMAKE_CURRENT_BINARY_DIR}/nroff-input.txt"
-        ERROR_QUIET)
-      # Save the option if it was valid
-      if(NROFF_MANOPT_OUTPUT)
-        message("Found *nroff option: -- ${_MANOPT}")
-        set(NROFF_MANOPT ${_MANOPT})
-        set(USE_MANUAL 1)
-        break()
-      endif()
-    endforeach()
-    # No need for the temporary file
-    file(REMOVE "${CMAKE_CURRENT_BINARY_DIR}/nroff-input.txt")
-    if(NOT USE_MANUAL)
-      message(WARNING "Found no *nroff option to get plaintext from man pages")
-    endif()
-  else()
-    message(WARNING "Found no *nroff program")
-  endif()
+CURL_NROFF_CHECK()
+find_package(Perl)
+
+CMAKE_DEPENDENT_OPTION(ENABLE_MANUAL "to provide the built-in manual"
+    ON "NROFF_USEFUL;PERL_FOUND"
+    OFF)
+
+if(NOT PERL_FOUND)
+  message(STATUS "Perl not found, testing disabled.")
+  set(BUILD_TESTING OFF)
+endif()
+if(ENABLE_MANUAL)
+  set(USE_MANUAL ON)
 endif()
-# Required for building manual, docs, tests
-find_package(Perl REQUIRED)
 
 # We need ansi c-flags, especially on HP
 set(CMAKE_C_FLAGS "${CMAKE_ANSI_CFLAGS} ${CMAKE_C_FLAGS}")
@@ -1149,8 +1131,12 @@ function(TRANSFORM_MAKEFILE_INC INPUT_FILE OUTPUT_FILE)
 
 endfunction()
 
-add_subdirectory(docs)
+if(USE_MANUAL)
+  add_subdirectory(docs)
+endif()
+
 add_subdirectory(lib)
+
 if(BUILD_CURL_EXE)
   add_subdirectory(src)
 endif()