Find FreeCAD path when used from external Python

src/App/Application.cpp

@@ -2281,27 +2281,64 @@ std::string Application::FindHomePath(const char* sCall)
 
 std::string Application::FindHomePath(const char* call)
 {
-    uint32_t sz = 0;
-    char *buf;
+    if (Py_IsInitialized()) {
+        // If we're initialised from an external Python, then there should be
+        // a path in the interpreter's sys.path that gets to FreeCAD.so .
+
+        auto pySysPath(PySys_GetObject("path"));
+        if ( PyList_Check(pySysPath) ) { 
+            // pySysPath should be a *PyList of strings - iterate through it
+            // backwards since the FreeCAD path was likely appended just before
+            // we were imported.
+            for (auto i( PyList_Size(pySysPath)-1 ); i >= 0 ; --i) {
+                auto pyPath( PyList_GetItem(pySysPath, i) );
+
+#if PY_MAJOR_VERSION >= 3
+                if ( !PyUnicode_Check(pyPath) )
+                    continue;
+                std::string path( PyUnicode_AsUTF8(pyPath) );
+#else 
+                if ( !PyString_Check(pyPath) )
+                    continue;
+                std::string path( PyString_AsString(pyPath) );
+#endif // #if/else PY_MAJOR_VERSION >= 3
+
+                // Try to find FreeCAD.so within this path
+                auto dylibPath( path + "/FreeCAD.so" );
+                if (access(dylibPath.c_str(), R_OK | X_OK) == 0) {
+
+                    // ...and the "home" path is one level up from that.
+                    return path + "/../";
+                }
+            }
+        }
 
-    _NSGetExecutablePath(NULL, &sz); //function only returns "sz" if first arg is to small to hold value
-    buf = new char[++sz];
+        std::cerr << "Couldn't determine path to FreeCAD.so via Python.\n";
 
-    if (_NSGetExecutablePath(buf, &sz) == 0) {
-        char resolved[PATH_MAX];
-        char* path = realpath(buf, resolved);
-        delete [] buf;
-
-        if (path) {
-            std::string Call(resolved), TempHomePath;
-            std::string::size_type pos = Call.find_last_of(PATHSEP);
-            TempHomePath.assign(Call,0,pos);
-            pos = TempHomePath.find_last_of(PATHSEP);
-            TempHomePath.assign(TempHomePath,0,pos+1);
-            return TempHomePath;
-        }
     } else {
-        delete [] buf;
+        uint32_t sz = 0;
+        char *buf;
+
+        // function only returns "sz" if first arg is too small to hold value
+        _NSGetExecutablePath(NULL, &sz); 
+        buf = new char[++sz];
+
+        if (_NSGetExecutablePath(buf, &sz) == 0) {
+            char resolved[PATH_MAX];
+            char* path = realpath(buf, resolved);
+            delete [] buf;
+
+            if (path) {
+                std::string Call(resolved), TempHomePath;
+                std::string::size_type pos = Call.find_last_of(PATHSEP);
+                TempHomePath.assign(Call,0,pos);
+                pos = TempHomePath.find_last_of(PATHSEP);
+                TempHomePath.assign(TempHomePath,0,pos+1);
+                return TempHomePath;
+            }
+        } else {
+            delete [] buf;
+        }
     }
 
     return call; // error

src/App/Application.h

@@ -336,9 +336,12 @@ class AppExport Application
     static void ParseOptions(int argc, char ** argv);
     /// checks if the environment is allreight
     //static void CheckEnv(void);
-    // search for the home path
+    /// Search for the FreeCAD home path based on argv[0] or Python interpreter
+    /*!
+     * There are multiple implementations of this method per-OS
+     */
     static std::string FindHomePath(const char* sCall);
-    /// print the help massage
+    /// Print the help message
     static void PrintInitHelp(void);
     /// figure out some things
     static void ExtractUserPath();