Revert "add_custom_command: Diagnose MAIN_DEPENDENCY limitation."

This reverts commit 242c3966 (add_custom_command: Diagnose
MAIN_DEPENDENCY limitation, 2015-03-09) and the follow up commit
b372a99a (UseSWIG: Do not use MAIN_DEPENDENCY on custom commands,
2015-03-26).

I misdiagnosed the underlying issue that prompted creation of policy CMP0057.
The actual issue surfaces when a single custom command's MAIN_DEPENDENCY
is listed in more than one target; this issue will have to be addressed
independently.

Help/policy/CMP0057.rst

@@ -1,21 +1,4 @@
 CMP0057
 -------
 
-Disallow multiple ``MAIN_DEPENDENCY`` specifications for the same file.
+This policy is reserved for future use.
-
-CMake 3.3 and above no longer allow the same input file to be used
-as a ``MAIN_DEPENDENCY`` in more than one custom command.
-
-Listing the same input file more than once in this context has not been
-supported by earlier versions either and would lead to build time issues
-but was not diagnosed.
-
-The ``OLD`` behavior for this policy is to allow using the same input file
-in a ``MAIN_DEPENDENCY`` specfication more than once.
-The ``NEW`` behavior is to disallow using the same input file in a
-``MAIN_DEPENDENCY`` specification more than once.
-
-This policy was introduced in CMake version 3.3.
-CMake version |release| warns when the policy is not set and uses
-``OLD`` behavior.  Use the :command:`cmake_policy` command to set
-it to ``OLD`` or ``NEW`` explicitly.

Help/release/dev/main_dependency_diagnostic.rst

@@ -1,6 +0,0 @@
-main_dependency_diagnostic
---------------------------
-
-* Listing the same input file as a MAIN_DEPENDENCY of a custom command
-  can lead to broken build time behavior.  This is now diagnosed.
-  See policy :policy:`CMP0057`.

Modules/UseSWIG.cmake

@@ -204,7 +204,8 @@ macro(SWIG_ADD_SOURCE_TO_MODULE name outfiles infile)
     ${swig_include_dirs}
     -o "${swig_generated_file_fullname}"
     "${swig_source_file_fullname}"
-    DEPENDS "${swig_source_file_fullname}" ${SWIG_MODULE_${name}_EXTRA_DEPS}
+    MAIN_DEPENDENCY "${swig_source_file_fullname}"
+    DEPENDS ${SWIG_MODULE_${name}_EXTRA_DEPS}
     COMMENT "Swig source")
   set_source_files_properties("${swig_generated_file_fullname}" ${swig_extra_generated_files}
     PROPERTIES GENERATED 1)

Source/cmMakefile.cxx

@@ -877,33 +877,6 @@ cmMakefile::AddCustomCommandToOutput(const std::vector<std::string>& outputs,
         }
       else
         {
-        std::ostringstream e;
-        cmake::MessageType messageType = cmake::AUTHOR_WARNING;
-        bool issueMessage = false;
-
-        switch(this->GetPolicyStatus(cmPolicies::CMP0057))
-          {
-          case cmPolicies::WARN:
-            e << (this->GetPolicies()->
-              GetPolicyWarning(cmPolicies::CMP0057)) << "\n";
-            issueMessage = true;
-          case cmPolicies::OLD:
-            break;
-          case cmPolicies::NEW:
-          case cmPolicies::REQUIRED_IF_USED:
-          case cmPolicies::REQUIRED_ALWAYS:
-            issueMessage = true;
-            messageType = cmake::FATAL_ERROR;
-            break;
-          }
-
-        if(issueMessage)
-          {
-          e << "\"" << main_dependency << "\" can only be specified as a "
-            "custom command MAIN_DEPENDENCY once.";
-          IssueMessage(messageType, e.str());
-          }
-
         // The existing custom command is different.  We need to
         // generate a rule file for this new command.
         file = 0;

Source/cmPolicies.cxx

@@ -376,11 +376,6 @@ cmPolicies::cmPolicies()
     "Honor link flags in try_compile() source-file signature.",
     3,2,0, cmPolicies::WARN);
 
-  this->DefinePolicy(
-    CMP0057, "CMP0057",
-    "Disallow multiple MAIN_DEPENDENCY specifications for the same file.",
-    3,3,0, cmPolicies::WARN);
-
   this->DefinePolicy(
     CMP0058, "CMP0058",
     "Ninja requires custom command byproducts to be explicit.",

Source/cmPolicies.h

@@ -113,8 +113,6 @@ public:
     /// or keywords when unquoted.
     CMP0055, ///< Strict checking for break() command.
     CMP0056, ///< Honor link flags in try_compile() source-file signature.
-    CMP0057, ///< Disallow multiple MAIN_DEPENDENCY specifications
-    /// for the same file.
     CMP0058, ///< Ninja requires custom command byproducts to be explicit
     CMP0059, ///< Do not treat ``DEFINITIONS`` as a built-in directory
     /// property.

Tests/RunCMake/CMP0057/CMP0057-NEW-result.txt

@@ -1 +0,0 @@
-1

Tests/RunCMake/CMP0057/CMP0057-NEW-stderr.txt

@@ -1,4 +0,0 @@
-CMake Error at CMP0057-NEW.cmake:8 \(add_custom_command\):
-  "input.txt" can only be specified as a custom command MAIN_DEPENDENCY once.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)

Tests/RunCMake/CMP0057/CMP0057-NEW.cmake

@@ -1,13 +0,0 @@
-cmake_policy(SET CMP0057 NEW)
-
-add_custom_command(OUTPUT out1
-  COMMAND ${CMAKE_COMMAND} -E echo out1
-  MAIN_DEPENDENCY input.txt
-)
-
-add_custom_command(OUTPUT out2
-  COMMAND ${CMAKE_COMMAND} -E echo out2
-  MAIN_DEPENDENCY input.txt
-)
-
-add_custom_target(mytarget1 ALL DEPENDS out1 out2)

Tests/RunCMake/CMP0057/CMP0057-OLD.cmake

@@ -1,13 +0,0 @@
-cmake_policy(SET CMP0057 OLD)
-
-add_custom_command(OUTPUT out1
-  COMMAND ${CMAKE_COMMAND} -E echo out1
-  MAIN_DEPENDENCY input.txt
-)
-
-add_custom_command(OUTPUT out2
-  COMMAND ${CMAKE_COMMAND} -E echo out2
-  MAIN_DEPENDENCY input.txt
-)
-
-add_custom_target(mytarget1 ALL DEPENDS out1 out2)

Tests/RunCMake/CMP0057/CMP0057-WARN-stderr.txt

@@ -1,9 +0,0 @@
-CMake Warning \(dev\) at CMP0057-WARN.cmake:6 \(add_custom_command\):
-  Policy CMP0057 is not set: Disallow multiple MAIN_DEPENDENCY specifications
-  for the same file.  Run "cmake --help-policy CMP0057" for policy details.
-  Use the cmake_policy command to set the policy and suppress this warning.
-
-  "input.txt" can only be specified as a custom command MAIN_DEPENDENCY once.
-Call Stack \(most recent call first\):
-  CMakeLists.txt:3 \(include\)
-This warning is for project developers.  Use -Wno-dev to suppress it.

Tests/RunCMake/CMP0057/CMP0057-WARN.cmake

@@ -1,11 +0,0 @@
-add_custom_command(OUTPUT out1
- COMMAND ${CMAKE_COMMAND} -E echo out1
-  MAIN_DEPENDENCY input.txt
-)
-
-add_custom_command(OUTPUT out2
-  COMMAND ${CMAKE_COMMAND} -E echo out2
-  MAIN_DEPENDENCY input.txt
-)
-
-add_custom_target(mytarget1 ALL DEPENDS out1 out2)

Tests/RunCMake/CMP0057/CMP0057-once_is_ok.cmake

@@ -1,8 +0,0 @@
-cmake_policy(SET CMP0057 NEW)
-
-add_custom_command(OUTPUT out1
-  COMMAND ${CMAKE_COMMAND} -E echo out1
-  MAIN_DEPENDENCY input.txt
-)
-
-add_custom_target(mytarget1 ALL DEPENDS out1)

Tests/RunCMake/CMP0057/CMakeLists.txt

@@ -1,3 +0,0 @@
-cmake_minimum_required(VERSION 3.1)
-project(${RunCMake_TEST} NONE)
-include(${RunCMake_TEST}.cmake)

Tests/RunCMake/CMP0057/RunCMakeTest.cmake

@@ -1,7 +0,0 @@
-include(RunCMake)
-
-run_cmake(CMP0057-OLD)
-run_cmake(CMP0057-NEW)
-run_cmake(CMP0057-WARN)
-
-run_cmake(CMP0057-once_is_ok)

Tests/RunCMake/CMakeLists.txt

@@ -63,7 +63,6 @@ add_RunCMake_test(CMP0051)
 add_RunCMake_test(CMP0053)
 add_RunCMake_test(CMP0054)
 add_RunCMake_test(CMP0055)
-add_RunCMake_test(CMP0057)
 add_RunCMake_test(CMP0059)
 add_RunCMake_test(CMP0060)
 if(CMAKE_GENERATOR STREQUAL "Ninja")