FetchContent: Give access to the terminal for download and update

A main scenario where this is needed is when a git operation
needs the password to a private key and asks for it on the
console. Without this change, such operations can appear to
hang indefinitely with no prompt if QUIET is in effect (which it
is by default).

Another scenario this addresses is when progress of a
download or update should be shown. Without this change,
all such progress is buffered with some generators and will
only be shown at the end, which defeats the purpose of logging
any progress to begin with.

Relates: #18238

Modules/FetchContent.cmake

@@ -691,6 +691,13 @@ function(__FetchContent_directPopulate contentName)
       BUILD_COMMAND
       INSTALL_COMMAND
       TEST_COMMAND
+      # We force both of these to be ON since we are always executing serially
+      # and we want all steps to have access to the terminal in case they
+      # need input from the command line (e.g. ask for a private key password)
+      # or they want to provide timely progress. We silently absorb and
+      # discard these if they are set by the caller.
+      USES_TERMINAL_DOWNLOAD
+      USES_TERMINAL_UPDATE
   )
   set(multiValueArgs "")
 

Modules/FetchContent/CMakeLists.cmake.in

@@ -18,4 +18,6 @@ ExternalProject_Add(${contentName}-populate
                     BUILD_COMMAND       ""
                     INSTALL_COMMAND     ""
                     TEST_COMMAND        ""
+                    USES_TERMINAL_DOWNLOAD  YES
+                    USES_TERMINAL_UPDATE    YES
 )

Tests/RunCMake/FetchContent/CMakeLists.txt

@@ -1,3 +1,7 @@
 cmake_minimum_required(VERSION 3.9)
 project(${RunCMake_TEST} NONE)
+
+# Tests assume no previous downloads in the output directory
+file(REMOVE_RECURSE ${CMAKE_CURRENT_BINARY_DIR}/_deps)
+
 include(${RunCMake_TEST}.cmake)

Tests/RunCMake/FetchContent/RunCMakeTest.cmake

@@ -10,6 +10,7 @@ run_cmake(SameGenerator)
 run_cmake(VarDefinitions)
 run_cmake(GetProperties)
 run_cmake(DirOverrides)
+run_cmake(UsesTerminalOverride)
 
 # We need to pass through CMAKE_GENERATOR and CMAKE_MAKE_PROGRAM
 # to ensure the test can run on machines where the build tool

Tests/RunCMake/FetchContent/UsesTerminalOverride-stdout.txt

@@ -0,0 +1,2 @@
+Logged from t1 download step
++.*Logged from t2 download step

Tests/RunCMake/FetchContent/UsesTerminalOverride.cmake

@@ -0,0 +1,17 @@
+include(FetchContent)
+
+set(FETCHCONTENT_QUIET NO)
+
+FetchContent_Declare(
+  t1
+  DOWNLOAD_COMMAND ${CMAKE_COMMAND} -E echo "Logged from t1 download step"
+  USES_TERMINAL_DOWNLOAD NO
+
+)
+FetchContent_Populate(t1)
+
+FetchContent_Populate(
+  t2
+  DOWNLOAD_COMMAND ${CMAKE_COMMAND} -E echo "Logged from t2 download step"
+  USES_TERMINAL_DOWNLOAD NO
+)