ExternalProject: Fix ENVIRONMENT_MODIFICATION with spaces in values

Fix commit e301cbffcc (ExternalProject: Set environment variables,
2025-04-09, v4.2.0-rc1~480^2) to quote arguments for ``EVAL CODE``,
used since commit cbf2daeed0 (ExternalProject: Preserve empty string
arguments, 2020-05-15, v3.18.0-rc1~99^2~1).

Fixes: #27876

Modules/ExternalProject.cmake

@@ -2808,7 +2808,8 @@ function(_ep_add_configure_command name)
     PROPERTY _EP_CONFIGURE_ENVIRONMENT_MODIFICATION
   )
   if(environment)
-    set(environment "ENVIRONMENT_MODIFICATION" ${environment})
+    string(JOIN "]==] [==[" environment ${environment})
+    set(environment "ENVIRONMENT_MODIFICATION [==[${environment}]==]")
   endif()
 
   get_property(log
@@ -2927,7 +2928,8 @@ function(_ep_add_build_command name)
     PROPERTY _EP_BUILD_ENVIRONMENT_MODIFICATION
   )
   if(environment)
-    set(environment ENVIRONMENT_MODIFICATION ${environment})
+    string(JOIN "]==] [==[" environment ${environment})
+    set(environment "ENVIRONMENT_MODIFICATION [==[${environment}]==]")
   endif()
 
   set(__cmdQuoted)
@@ -3022,7 +3024,8 @@ function(_ep_add_install_command name)
     PROPERTY _EP_INSTALL_ENVIRONMENT_MODIFICATION
   )
   if(environment)
-    set(environment ENVIRONMENT_MODIFICATION ${environment})
+    string(JOIN "]==] [==[" environment ${environment})
+    set(environment "ENVIRONMENT_MODIFICATION [==[${environment}]==]")
   endif()
 
   set(__cmdQuoted)
@@ -3110,7 +3113,8 @@ function(_ep_add_test_command name)
       PROPERTY _EP_TEST_ENVIRONMENT_MODIFICATION
     )
     if(environment)
-      set(environment ENVIRONMENT_MODIFICATION ${environment})
+      string(JOIN "]==] [==[" environment ${environment})
+      set(environment "ENVIRONMENT_MODIFICATION [==[${environment}]==]")
     endif()
 
     set(__cmdQuoted)

Tests/RunCMake/ExternalProject/EnvVars-build-stdout-windows.txt

@@ -1,11 +1,11 @@
 .*(Performing custom step for 'CustomCommand'|CustomCommand-custom).*
  *-- Variable - CustomVar: custom.*
- *-- Variable - CustomVar2: custom2.*
+ *-- Variable - CustomVar2: custom two.*
  *-- Stage: custom
  *-- Separator: ;
  *-- List: 1;2;3
 .*(Performing configure step for 'CustomCommand'|CustomCommand-configure).*
- *-- Stage: config
+ *-- Stage: config step
  *-- Separator: ;
  *-- List: 4;5;6
  *-- MYLIST:
@@ -15,15 +15,15 @@
  *-- Variable - Stage: config.*
  *-- Variable - ListVar: 4;5;6
 .*(Performing build step for 'CustomCommand'|CustomCommand-build).*
- *-- Stage: build
+ *-- Stage: build step
  *-- Separator: ;
  *-- List: 4;5;6
 .*(Performing install step for 'CustomCommand'|CustomCommand-install).*
- *-- Stage: install
+ *-- Stage: install step
  *-- Separator: ;
  *-- List: 4;5;6
 .*(Performing test step for 'CustomCommand'|CustomCommand-test).*
- *-- Stage: test
+ *-- Stage: test step
  *-- Separator: ;
  *-- List: 4;5;6
 .*(Performing configure step for 'DefaultCommand'|DefaultCommand-configure).*

Tests/RunCMake/ExternalProject/EnvVars-build-stdout.txt

@@ -1,11 +1,11 @@
 .*(Performing custom step for 'CustomCommand'|CustomCommand-custom).*
  *-- Variable - CustomVar: custom.*
- *-- Variable - CustomVar2: custom2.*
+ *-- Variable - CustomVar2: custom two.*
  *-- Stage: custom
  *-- Separator: ;
  *-- List: 1;2;3
 .*(Performing configure step for 'CustomCommand'|CustomCommand-configure).*
- *-- Stage: config
+ *-- Stage: config step
  *-- Separator: ;
  *-- List: 4;5;6
  *-- MYLIST:
@@ -15,15 +15,15 @@
  *-- Variable - Stage: config.*
  *-- Variable - ListVar: 4;5;6
 .*(Performing build step for 'CustomCommand'|CustomCommand-build).*
- *-- Stage: build
+ *-- Stage: build step
  *-- Separator: ;
  *-- List: 4;5;6
 .*(Performing install step for 'CustomCommand'|CustomCommand-install).*
- *-- Stage: install
+ *-- Stage: install step
  *-- Separator: ;
  *-- List: 4;5;6
 .*(Performing test step for 'CustomCommand'|CustomCommand-test).*
- *-- Stage: test
+ *-- Stage: test step
  *-- Separator: ;
  *-- List: 4;5;6
 .*(Performing configure step for 'DefaultCommand'|DefaultCommand-configure).*

Tests/RunCMake/ExternalProject/EnvVars.cmake

@@ -21,23 +21,23 @@ ExternalProject_Add(CustomCommand
   COMMAND
   COMMAND "${CMAKE_COMMAND}" -DVARNAME=ListVar -P ${ScriptPath}
   CONFIGURE_ENVIRONMENT_MODIFICATION
-    Stage=set:config
+    "Stage=set:config step"
     ListVar=set:4,5,6
     ListSeparator=set:,
   BUILD_COMMAND "${CMAKE_COMMAND}" -P ${ScriptPath}
   BUILD_ENVIRONMENT_MODIFICATION
-    Stage=set:build
+    "Stage=set:build step"
     ListVar=set:4,5,6
     ListSeparator=set:,
   INSTALL_COMMAND "${CMAKE_COMMAND}" -P ${ScriptPath}
   INSTALL_ENVIRONMENT_MODIFICATION
     InstallVar=set:install
-    Stage=set:install
+    "Stage=set:install step"
     ListVar=set:4,5,6
     ListSeparator=set:,
   TEST_COMMAND "${CMAKE_COMMAND}" -P ${ScriptPath}
   TEST_ENVIRONMENT_MODIFICATION
-    Stage=set:test
+    "Stage=set:test step"
     ListVar=set:4,5,6
     ListSeparator=set:,)
 
@@ -48,7 +48,7 @@ ExternalProject_Add_Step(CustomCommand custom
   COMMAND "${CMAKE_COMMAND}" -P ${ScriptPath}
   ENVIRONMENT_MODIFICATION
     CustomVar=set:custom
-    CustomVar2=set:custom2
+    "CustomVar2=set:custom two"
     Stage=set:custom
     ListVar=set:1,2,3
     ListSeparator=set:,)