Teach link_directories to recognize relative paths

We create CMake Policy CMP0015 to make link_directories() treat relative
paths with respect to the source tree while retaining compatibility.
This makes it consistent with include_directories() and other commands.

Changes based on patch from Alex.  See issue #9697.

Source/cmLinkDirectoriesCommand.cxx

@@ -23,10 +23,48 @@ bool cmLinkDirectoriesCommand
   for(std::vector<std::string>::const_iterator i = args.begin();
       i != args.end(); ++i)
     {
-    std::string unixPath = *i;
+    this->AddLinkDir(*i);
-    cmSystemTools::ConvertToUnixSlashes(unixPath);
-    this->Makefile->AddLinkDirectory(unixPath.c_str());
     }
   return true;
 }
 
+//----------------------------------------------------------------------------
+void cmLinkDirectoriesCommand::AddLinkDir(std::string const& dir)
+{
+  std::string unixPath = dir;
+  cmSystemTools::ConvertToUnixSlashes(unixPath);
+  if(!cmSystemTools::FileIsFullPath(unixPath.c_str()))
+    {
+    bool convertToAbsolute = false;
+    cmOStringStream e;
+    e << "This command specifies the relative path\n"
+      << "  " << unixPath << "\n"
+      << "as a link directory.\n";
+    cmPolicies* policies = this->Makefile->GetPolicies();
+    switch (this->Makefile->GetPolicyStatus(cmPolicies::CMP0015))
+      {
+      case cmPolicies::WARN:
+        e << policies->GetPolicyWarning(cmPolicies::CMP0015);
+        this->Makefile->IssueMessage(cmake::AUTHOR_WARNING, e.str());
+      case cmPolicies::OLD:
+        // OLD behavior does not convert
+        break;
+      case cmPolicies::REQUIRED_IF_USED:
+      case cmPolicies::REQUIRED_ALWAYS:
+        e << policies->GetRequiredPolicyError(cmPolicies::CMP0015);
+        this->Makefile->IssueMessage(cmake::FATAL_ERROR, e.str());
+      case cmPolicies::NEW:
+        // NEW behavior converts
+        convertToAbsolute = true;
+        break;
+      }
+    if (convertToAbsolute)
+      {
+      std::string tmp = this->Makefile->GetStartDirectory();
+      tmp += "/";
+      tmp += unixPath;
+      unixPath = tmp;
+      }
+    }
+  this->Makefile->AddLinkDirectory(unixPath.c_str());
+}

Source/cmLinkDirectoriesCommand.h

@@ -70,6 +70,8 @@ public:
     }
   
   cmTypeMacro(cmLinkDirectoriesCommand, cmCommand);
+private:
+  void AddLinkDir(std::string const& dir);
 };
 
 

Source/cmPolicies.cxx

@@ -406,6 +406,21 @@ cmPolicies::cmPolicies()
     "The OLD behavior for this policy is to silently ignore the problem.  "
     "The NEW behavior for this policy is to report an error.",
     2,8,0, cmPolicies::WARN);
+
+    this->DefinePolicy(
+    CMP0015, "CMP0015",
+    "link_directories() treats paths relative to the source dir.",
+    "In CMake 2.6.4 and lower the link_directories() command passed relative "
+    "paths unchanged to the linker.  "
+    "In CMake 2.8.1 and above the link_directories() command prefers to "
+    "interpret relative paths with respect to CMAKE_CURRENT_SOURCE_DIR, "
+    "which is consistent with include_directories() and other commands.  "
+    "The OLD behavior for this policy is to use relative paths verbatim in "
+    "the linker command.  "
+    "The NEW behavior for this policy is to convert relative paths to "
+    "absolute paths by appending the relative path to "
+    "CMAKE_CURRENT_SOURCE_DIR.",
+    2,8,1, cmPolicies::WARN);
 }
 
 cmPolicies::~cmPolicies()

Source/cmPolicies.h

@@ -50,6 +50,7 @@ public:
     CMP0012, // Recognize numbers and boolean constants in if()
     CMP0013, // Duplicate binary directories not allowed
     CMP0014, // Input directories must have CMakeLists.txt
+    CMP0015, // link_directories() treats paths relative to source dir
 
     // Always the last entry.  Useful mostly to avoid adding a comma
     // the last policy when adding a new one.