Xcode: Use deterministic object ids for product file references

Follow-up commit 1fa2ec1bbd (Xcode: Use deterministic object ids for
targets, 2024-04-04, v3.30.0-rc1~263^2).  Each target's product
PBXFileReference (the libfoo.a / foo entries under the Products group)
was created with a random object id on every regeneration.  When a
CMake-generated Xcode project is embedded in another Xcode project, that
parent keeps the product reference's id in its remoteGlobalIDString; a
random id means the reference no longer resolves and the link falls back
to a bare `-l` flag (e.g. `ld: library 'foo' not found`).

Derive the product PBXFileReference id from the target name and the
build-tree-relative product path, the same hashing path already used for
the target object id.  The id is now stable across regenerations and
independent of the absolute build tree location.

Source/cmGlobalXCodeGenerator.cxx

@@ -3583,7 +3583,10 @@ cmXCodeObject* cmGlobalXCodeGenerator::CreateXCodeTarget(
   target->AddAttribute("name", this->CreateString(gtgt->GetName()));
   target->AddAttribute("productName", this->CreateString(gtgt->GetName()));
 
-  cmXCodeObject* fileRef = this->CreateObject(cmXCodeObject::PBXFileReference);
+  cmXCodeObject* fileRef =
+    this->CreateObject(cmXCodeObject::PBXFileReference,
+                       cmStrCat("PBXFileReference:product:", gtgt->GetName(),
+                                ':', targetBinaryPath));
   if (char const* fileType = this->GetTargetFileType(gtgt)) {
     fileRef->AddAttribute("explicitFileType", this->CreateString(fileType));
   }

Tests/RunCMake/XcodeProject/DeterministicProductIds-check.cmake

@@ -0,0 +1,49 @@
+# Collect "path -> object id" for every product PBXFileReference (those under
+# BUILT_PRODUCTS_DIR) in a generated project.pbxproj.
+function(read_product_ids pbxproj out_var)
+  if(NOT EXISTS "${pbxproj}")
+    set(RunCMake_TEST_FAILED "Project file does not exist:\n  ${pbxproj}" PARENT_SCOPE)
+    return()
+  endif()
+  set(ids "")
+  file(STRINGS "${pbxproj}" lines)
+  foreach(line IN LISTS lines)
+    if(line MATCHES "isa = PBXFileReference;" AND line MATCHES "sourceTree = BUILT_PRODUCTS_DIR;")
+      string(REGEX MATCH "^[ \t]*([0-9A-F]+) " _ "${line}")
+      set(id "${CMAKE_MATCH_1}")
+      string(REGEX MATCH "path = ([^;]+);" _ "${line}")
+      set(path "${CMAKE_MATCH_1}")
+      list(APPEND ids "${path}=${id}")
+    endif()
+  endforeach()
+  list(SORT ids)
+  set(${out_var} "${ids}" PARENT_SCOPE)
+endfunction()
+
+set(pbxproj "${RunCMake_TEST_BINARY_DIR}/DeterministicProductIds.xcodeproj/project.pbxproj")
+read_product_ids("${pbxproj}" this_ids)
+if(RunCMake_TEST_FAILED)
+  return()
+endif()
+
+if(NOT this_ids)
+  set(RunCMake_TEST_FAILED "No product PBXFileReference entries found in\n  ${pbxproj}")
+  return()
+endif()
+
+# On the second generation, compare against the first build tree. The ids must
+# be byte-identical even though the build tree path differs.
+if(DEFINED DeterministicProductIds_FirstBinaryDir)
+  read_product_ids(
+    "${DeterministicProductIds_FirstBinaryDir}/DeterministicProductIds.xcodeproj/project.pbxproj"
+    first_ids)
+  if(RunCMake_TEST_FAILED)
+    return()
+  endif()
+  if(NOT this_ids STREQUAL first_ids)
+    string(REPLACE ";" "\n  " a "${first_ids}")
+    string(REPLACE ";" "\n  " b "${this_ids}")
+    set(RunCMake_TEST_FAILED
+      "Product PBXFileReference ids are not deterministic across build trees.\nFirst:\n  ${a}\nSecond:\n  ${b}")
+  endif()
+endif()

Tests/RunCMake/XcodeProject/DeterministicProductIds.cmake

@@ -0,0 +1,10 @@
+enable_language(C)
+
+# Each target's product PBXFileReference must get a deterministic object id so
+# that a parent project embedding this one can keep a stable remoteGlobalIDString.
+add_library(productStatic STATIC empty.c)
+add_library(productShared SHARED empty.c)
+add_executable(productExe empty.c)
+
+# A target in a subdirectory exercises the relative-path component of the key.
+add_subdirectory(DeterministicProductIdsSub)

Tests/RunCMake/XcodeProject/DeterministicProductIdsSub/CMakeLists.txt

@@ -0,0 +1 @@
+add_library(productSubStatic STATIC ../empty.c)

Tests/RunCMake/XcodeProject/RunCMakeTest.cmake

@@ -14,6 +14,19 @@ run_cmake_with_options(ArchsStandard "-DCMAKE_OSX_ARCHITECTURES=$(ARCHS_STANDARD
 run_cmake(ExplicitCMakeLists)
 run_cmake(ImplicitCMakeLists)
 run_cmake(InterfaceLibSources)
+
+function(DeterministicProductIds)
+  # Generate the same project into two separate build trees and verify that the
+  # product PBXFileReference object ids are byte-identical: deterministic and
+  # independent of the build tree location.
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/DeterministicProductIds-build1)
+  run_cmake(DeterministicProductIds)
+  set(DeterministicProductIds_FirstBinaryDir ${RunCMake_TEST_BINARY_DIR})
+  set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/DeterministicProductIds-build2)
+  run_cmake(DeterministicProductIds)
+endfunction()
+DeterministicProductIds()
+
 run_cmake_with_options(SearchPaths -DCMAKE_CONFIGURATION_TYPES=Debug)
 run_cmake_with_options(InheritedParameters -DCMake_TEST_Swift=${CMake_TEST_Swift})
 

Tests/RunCMake/XcodeProject/empty.c

@@ -0,0 +1,4 @@
+int productSymbol(void)
+{
+  return 0;
+}