Makefile: Fix regression in dependencies on relative includes

Since commit a13a5c948e (Replace use of CollapseCombinedPath with
CollapseFullPath, 2019-03-19, v3.15.0-rc1~361^2~1), one code path now
calls `CollapseFullPath` with a base path that may be relative.
Backport KWSys commit c6f8e24a3 (SystemTools: Fix CollapseFullPath with
relative base path, 2019-07-24) to handle such base paths.

This case occurs when a build tree is placed in a directory inside a
source tree such that CMake is willing to generate a relative path from
the build tree to the source tree.  Add a test covering this case.

Fixes: #19507

2 files changed, 12 insertions, 3 deletions

diff --git a/Source/kwsys/SystemTools.cxx b/Source/kwsys/SystemTools.cxx
index 2135913..ae7a18a 100644
--- a/Source/kwsys/SystemTools.cxx
+++ b/Source/kwsys/SystemTools.cxx
@@ -3394,8 +3394,13 @@ static void SystemToolsAppendComponents(
   static const std::string cur = ".";
   for (std::vector<std::string>::const_iterator i = first; i != last; ++i) {
     if (*i == up) {
-      if (out_components.size() > 1) {
+      // Remove the previous component if possible.  Ignore ../ components
+      // that try to go above the root.  Keep ../ components if they are
+      // at the beginning of a relative path (base path is relative).
+      if (out_components.size() > 1 && out_components.back() != up) {
         out_components.resize(out_components.size() - 1);
+      } else if (!out_components.empty() && out_components[0].empty()) {
+        out_components.emplace_back(std::move(*i));
       }
     } else if (!i->empty() && *i != cur) {
 #if __cplusplus >= 201103L || (defined(_MSVC_LANG) && _MSVC_LANG >= 201103L)
diff --git a/Source/kwsys/testSystemTools.cxx b/Source/kwsys/testSystemTools.cxx
index 9a40b53..ffa6a29 100644
--- a/Source/kwsys/testSystemTools.cxx
+++ b/Source/kwsys/testSystemTools.cxx
@@ -684,9 +684,10 @@ static bool CheckRelativePaths()
 }
 
 static bool CheckCollapsePath(const std::string& path,
-                              const std::string& expected)
+                              const std::string& expected,
+                              const char* base = nullptr)
 {
-  std::string result = kwsys::SystemTools::CollapseFullPath(path);
+  std::string result = kwsys::SystemTools::CollapseFullPath(path, base);
   if (!kwsys::SystemTools::ComparePath(expected, result)) {
     std::cerr << "CollapseFullPath(" << path << ")  yielded " << result
               << " instead of " << expected << std::endl;
@@ -710,6 +711,9 @@ static bool CheckCollapsePath()
   res &= CheckCollapsePath("C:/", "C:/");
   res &= CheckCollapsePath("C:/../", "C:/");
   res &= CheckCollapsePath("C:/../../", "C:/");
+  res &= CheckCollapsePath("../b", "../../b", "../");
+  res &= CheckCollapsePath("../a/../b", "../b", "../rel");
+  res &= CheckCollapsePath("a/../b", "../rel/b", "../rel");
   return res;
 }