find_library: Fix repeat call after changing directory content (#15293)

We use cmGlobalGenerator::GetDirectoryContent to avoid repeating
directory listings.  However, GetDirectoryContent loads content from
disk at most once.  This breaks find_library calls that occur when disk
content has changed since preceding find_library calls.

Teach cmGlobalGenerator::GetDirectoryContent to save the directory
modification time when content is loaded and re-load content if it
changes.

Create a RunCMake.find_library test with a case covering this.

2 files changed, 30 insertions, 20 deletions

diff --git a/Source/cmGlobalGenerator.cxx b/Source/cmGlobalGenerator.cxx
index 29ab7d0..dd7fbc8 100644
--- a/Source/cmGlobalGenerator.cxx
+++ b/Source/cmGlobalGenerator.cxx
@@ -2725,7 +2725,9 @@ void cmGlobalGenerator::AddToManifest(const std::string& config,
   // Add to the content listing for the file's directory.
   std::string dir = cmSystemTools::GetFilenamePath(f);
   std::string file = cmSystemTools::GetFilenameName(f);
-  this->DirectoryContentMap[dir].insert(file);
+  DirectoryContent& dc = this->DirectoryContentMap[dir];
+  dc.Generated.insert(file);
+  dc.All.insert(file);
 }
 
 //----------------------------------------------------------------------------
@@ -2733,25 +2735,32 @@ std::set<std::string> const&
 cmGlobalGenerator::GetDirectoryContent(std::string const& dir, bool needDisk)
 {
   DirectoryContent& dc = this->DirectoryContentMap[dir];
-  if(needDisk && !dc.LoadedFromDisk)
+  if(needDisk)
     {
-    // Load the directory content from disk.
-    cmsys::Directory d;
-    if(d.Load(dir))
+    long mt = cmSystemTools::ModifiedTime(dir);
+    if (mt != dc.LastDiskTime)
       {
-      unsigned long n = d.GetNumberOfFiles();
-      for(unsigned long i = 0; i < n; ++i)
+      // Reset to non-loaded directory content.
+      dc.All = dc.Generated;
+
+      // Load the directory content from disk.
+      cmsys::Directory d;
+      if(d.Load(dir))
         {
-        const char* f = d.GetFile(i);
-        if(strcmp(f, ".") != 0 && strcmp(f, "..") != 0)
+        unsigned long n = d.GetNumberOfFiles();
+        for(unsigned long i = 0; i < n; ++i)
           {
-          dc.insert(f);
+          const char* f = d.GetFile(i);
+          if(strcmp(f, ".") != 0 && strcmp(f, "..") != 0)
+            {
+            dc.All.insert(f);
+            }
           }
         }
+      dc.LastDiskTime = mt;
       }
-    dc.LoadedFromDisk = true;
     }
-  return dc;
+  return dc.All;
 }
 
 //----------------------------------------------------------------------------
diff --git a/Source/cmGlobalGenerator.h b/Source/cmGlobalGenerator.h
index 6b75298..08f061a 100644
--- a/Source/cmGlobalGenerator.h
+++ b/Source/cmGlobalGenerator.h
@@ -255,9 +255,9 @@ public:
   cmTargetManifest const& GetTargetManifest() const
     { return this->TargetManifest; }
 
-  /** Get the content of a directory.  Directory listings are loaded
-      from disk at most once and cached.  During the generation step
-      the content will include the target files to be built even if
+  /** Get the content of a directory.  Directory listings are cached
+      and re-loaded from disk only when modified.  During the generation
+      step the content will include the target files to be built even if
       they do not yet exist.  */
   std::set<std::string> const& GetDirectoryContent(std::string const& dir,
                                                    bool needDisk = true);
@@ -486,13 +486,14 @@ private:
   virtual const char* GetBuildIgnoreErrorsFlag() const { return 0; }
 
   // Cache directory content and target files to be built.
-  struct DirectoryContent: public std::set<std::string>
+  struct DirectoryContent
   {
-    typedef std::set<std::string> derived;
-    bool LoadedFromDisk;
-    DirectoryContent(): LoadedFromDisk(false) {}
+    long LastDiskTime;
+    std::set<std::string> All;
+    std::set<std::string> Generated;
+    DirectoryContent(): LastDiskTime(-1) {}
     DirectoryContent(DirectoryContent const& dc):
-      derived(dc), LoadedFromDisk(dc.LoadedFromDisk) {}
+      LastDiskTime(dc.LastDiskTime), All(dc.All), Generated(dc.Generated) {}
   };
   std::map<std::string, DirectoryContent> DirectoryContentMap;