find_package(): Debug re-rooting behavior

find_package()'s debug mode provides information about which
prefixes are searched, but not which roots are prepended to each
prefix. Display this information if debugging is enabled.

Source/cmFindCommon.cxx

@@ -212,7 +212,8 @@ void cmFindCommon::SelectDefaultSearchModes()
   }
 }
 
-void cmFindCommon::RerootPaths(std::vector<std::string>& paths)
+void cmFindCommon::RerootPaths(std::vector<std::string>& paths,
+                               std::string* debugBuffer)
 {
 #if 0
   for(std::string const& p : paths)
@@ -238,17 +239,40 @@ void cmFindCommon::RerootPaths(std::vector<std::string>& paths)
     return;
   }
 
+  if (this->DebugMode && debugBuffer) {
+    *debugBuffer = cmStrCat(
+      *debugBuffer, "Prepending the following roots to each prefix:\n");
+  }
+
+  auto debugRoot = [this, debugBuffer](const std::string& name,
+                                       cmValue value) {
+    if (this->DebugMode && debugBuffer) {
+      *debugBuffer = cmStrCat(*debugBuffer, name, "\n");
+      cmList roots{ value };
+      if (roots.empty()) {
+        *debugBuffer = cmStrCat(*debugBuffer, "  none\n");
+      }
+      for (auto const& root : roots) {
+        *debugBuffer = cmStrCat(*debugBuffer, "  ", root, "\n");
+      }
+    }
+  };
+
   // Construct the list of path roots with no trailing slashes.
   cmList roots;
+  debugRoot("CMAKE_FIND_ROOT_PATH", rootPath);
   if (rootPath) {
     roots.assign(*rootPath);
   }
+  debugRoot("CMAKE_SYSROOT_COMPILE", sysrootCompile);
   if (sysrootCompile) {
     roots.emplace_back(*sysrootCompile);
   }
+  debugRoot("CMAKE_SYSROOT_LINK", sysrootLink);
   if (sysrootLink) {
     roots.emplace_back(*sysrootLink);
   }
+  debugRoot("CMAKE_SYSROOT", sysroot);
   if (sysroot) {
     roots.emplace_back(*sysroot);
   }
@@ -411,7 +435,8 @@ static void AddTrailingSlash(std::string& s)
     s += '/';
   }
 }
-void cmFindCommon::ComputeFinalPaths(IgnorePaths ignorePaths)
+void cmFindCommon::ComputeFinalPaths(IgnorePaths ignorePaths,
+                                     std::string* debugBuffer)
 {
   // Filter out ignored paths from the prefix list
   std::set<std::string> ignoredPaths;
@@ -430,7 +455,7 @@ void cmFindCommon::ComputeFinalPaths(IgnorePaths ignorePaths)
   }
 
   // Expand list of paths inside all search roots.
-  this->RerootPaths(this->SearchPaths);
+  this->RerootPaths(this->SearchPaths, debugBuffer);
 
   // Add a trailing slash to all paths to aid the search process.
   std::for_each(this->SearchPaths.begin(), this->SearchPaths.end(),

Source/cmFindCommon.h

@@ -81,7 +81,8 @@ protected:
   void InitializeSearchPathGroups();
 
   /** Place a set of search paths under the search roots.  */
-  void RerootPaths(std::vector<std::string>& paths);
+  void RerootPaths(std::vector<std::string>& paths,
+                   std::string* debugBuffer = nullptr);
 
   /** Get ignored paths from CMAKE_[SYSTEM_]IGNORE_PATH variables.  */
   void GetIgnoredPaths(std::vector<std::string>& ignore);
@@ -97,7 +98,8 @@ protected:
     No,
     Yes,
   };
-  void ComputeFinalPaths(IgnorePaths ignorePaths);
+  void ComputeFinalPaths(IgnorePaths ignorePaths,
+                         std::string* debugBuffer = nullptr);
 
   /** Compute the current default root path mode.  */
   void SelectDefaultRootPathMode();

Source/cmFindPackageCommand.cxx

@@ -2013,7 +2013,7 @@ void cmFindPackageCommand::ComputePrefixes()
   }
   this->FillPrefixesUserGuess();
 
-  this->ComputeFinalPaths(IgnorePaths::No);
+  this->ComputeFinalPaths(IgnorePaths::No, &this->DebugBuffer);
 }
 
 void cmFindPackageCommand::FillPrefixesPackageRedirect()

Tests/RunCMake/find_package/DebugRoot-stderr.txt

@@ -0,0 +1,52 @@
+^CMake Debug Log at DebugRoot\.cmake:[0-9]+ \(find_package\):
+  The internally managed CMAKE_FIND_PACKAGE_REDIRECTS_DIR\.
+
+    [^
+]*/Tests/RunCMake/find_package/DebugRoot-build/CMakeFiles/pkgRedirects
+
+  Paths specified by the find_package HINTS option\.
+
+    none
+
+  Paths specified by the find_package PATHS option\.
+
+    /DebugRoot
+
+  Prepending the following roots to each prefix:
+
+  CMAKE_FIND_ROOT_PATH
+
+    [^
+]*/Tests/RunCMake/find_package/DebugRoot/NoExist
+    [^
+]*/Tests/RunCMake/find_package/DebugRoot/Exist
+
+  CMAKE_SYSROOT_COMPILE
+
+    none
+
+  CMAKE_SYSROOT_LINK
+
+    none
+
+  CMAKE_SYSROOT
+
+    none
+
+  find_package considered the following locations for DebugRoot's Config
+  module:
+
+    [^
+]*/Tests/RunCMake/find_package/DebugRoot/NoExist/DebugRoot/DebugRootConfig\.cmake
+    [^
+]*/Tests/RunCMake/find_package/DebugRoot/NoExist/DebugRoot/debugroot-config\.cmake
+    [^
+]*/Tests/RunCMake/find_package/DebugRoot/Exist/DebugRoot/DebugRootConfig\.cmake
+
+  The file was found at
+
+    [^
+]*/Tests/RunCMake/find_package/DebugRoot/Exist/DebugRoot/DebugRootConfig.cmake
+
+Call Stack \(most recent call first\):
+  CMakeLists\.txt:[0-9]+ \(include\)$

Tests/RunCMake/find_package/DebugRoot.cmake

@@ -0,0 +1,15 @@
+set(CMAKE_FIND_ROOT_PATH ${CMAKE_CURRENT_LIST_DIR}/DebugRoot/NoExist ${CMAKE_CURRENT_LIST_DIR}/DebugRoot/Exist)
+set(CMAKE_FIND_DEBUG_MODE ON)
+find_package(DebugRoot
+  NO_DEFAULT_PATH
+  NO_PACKAGE_ROOT_PATH
+  NO_CMAKE_PATH
+  NO_CMAKE_ENVIRONMENT_PATH
+  NO_SYSTEM_ENVIRONMENT_PATH
+  NO_CMAKE_PACKAGE_REGISTRY
+  NO_CMAKE_SYSTEM_PATH
+  NO_CMAKE_INSTALL_PREFIX
+  NO_CMAKE_SYSTEM_PACKAGE_REGISTRY
+  PATHS /DebugRoot
+  )
+set(CMAKE_FIND_DEBUG_MODE OFF)

Tests/RunCMake/find_package/DebugRoot/Exist/DebugRoot/DebugRootConfig.cmake

@@ -0,0 +1 @@
+set(DebugRoot_FOUND TRUE)

Tests/RunCMake/find_package/RunCMakeTest.cmake

@@ -74,6 +74,7 @@ run_cmake(IgnorePrefixPath)
 run_cmake(REGISTRY_VIEW-no-view)
 run_cmake(REGISTRY_VIEW-wrong-view)
 run_cmake(REGISTRY_VIEW-propagated)
+run_cmake(DebugRoot)
 
 if(CMAKE_HOST_WIN32 AND MINGW)
   run_cmake(MSYSTEM_PREFIX)