ExternalProject: Honor CMAKE_TLS_VERIFY environment variable

Issue: #23608

Help/envvar/CMAKE_TLS_VERIFY.rst

@@ -9,3 +9,7 @@ Specify the default value for the :command:`file(DOWNLOAD)` and
 :command:`file(UPLOAD)` commands' ``TLS_VERIFY`` option.
 This environment variable is used if the option is not given
 and the :variable:`CMAKE_TLS_VERIFY` cmake variable is not set.
+
+This variable is also used by the :module:`ExternalProject` and
+:module:`FetchContent` modules for internal calls to
+:command:`file(DOWNLOAD)` and ``git clone``.

Modules/ExternalProject.cmake

@@ -243,22 +243,28 @@ URL
 ``TLS_VERIFY <bool>``
   Specifies whether certificate verification should be performed for
   ``https://`` URLs.  If this option is not provided, the value of the
-  :variable:`CMAKE_TLS_VERIFY` variable will be used instead (see
-  :command:`file(DOWNLOAD)`).
-  If that is also not set, certificate verification will not be performed.
+  :variable:`CMAKE_TLS_VERIFY` variable or the :envvar:`CMAKE_TLS_VERIFY`
+  environment variable will be used instead (see :command:`file(DOWNLOAD)`).
+  If neither of those is set, certificate verification will not be performed.
   In situations where ``URL_HASH`` cannot be provided, this option can
   be an alternative verification measure.
 
   This option also applies to ``git clone`` invocations, although the
-  default behavior is different.  If neither the ``TLS_VERIFY`` option
-  or :variable:`CMAKE_TLS_VERIFY` variable is specified, the behavior
-  will be determined by git's default (true) or a ``http.sslVerify``
-  git config option the user may have set at a global level.
+  default behavior is different.  If none of the ``TLS_VERIFY`` option,
+  :variable:`CMAKE_TLS_VERIFY` variable, or :envvar:`CMAKE_TLS_VERIFY`
+  environment variable is specified, the behavior will be determined by
+  git's default (true) or a ``http.sslVerify`` git config option the
+  user may have set at a global level.
 
   .. versionchanged:: 3.6
 
     Previously this option did not apply to ``git clone`` invocations.
 
+  .. versionchanged:: 3.30
+
+    Previously the :envvar:`CMAKE_TLS_VERIFY` environment variable
+    was not checked.
+
 ``TLS_CAINFO <file>``
   Specify a custom certificate authority file to use if ``TLS_VERIFY``
   is enabled. If this option is not specified, the value of the
@@ -1397,8 +1403,12 @@ endfunction()
 
 function(_ep_get_tls_verify name tls_verify_var)
   get_property(tls_verify TARGET ${name} PROPERTY _EP_TLS_VERIFY)
-  if("x${tls_verify}" STREQUAL "x" AND DEFINED CMAKE_TLS_VERIFY)
-    set(tls_verify "${CMAKE_TLS_VERIFY}")
+  if("x${tls_verify}" STREQUAL "x")
+    if(NOT "x${CMAKE_TLS_VERIFY}" STREQUAL "x")
+      set(tls_verify "${CMAKE_TLS_VERIFY}")
+    elseif(NOT "x$ENV{CMAKE_TLS_VERIFY}" STREQUAL "x")
+      set(tls_verify "$ENV{CMAKE_TLS_VERIFY}")
+    endif()
   endif()
   set("${tls_verify_var}" "${tls_verify}" PARENT_SCOPE)
 endfunction()