diff --git a/compiler/src/dmd/common/file.d b/compiler/src/dmd/common/file.d
index 98ee13e031b0..52da6ee07925 100644
--- a/compiler/src/dmd/common/file.d
+++ b/compiler/src/dmd/common/file.d
@@ -14,15 +14,23 @@
 
 module dmd.common.file;
 
+import core.stdc.stdio;
+import core.stdc.stdlib;
+import core.stdc.string;
+import core.stdc.limits;
+
 import core.stdc.errno : errno;
 import core.stdc.stdio : fprintf, remove, rename, stderr;
 import core.stdc.stdlib;
 import core.stdc.string : strerror, strlen, memcpy;
 
 import dmd.common.smallbuffer;
+import dmd.root.filename;
+import dmd.root.rmem;
 
 version (Windows)
 {
+    import core.stdc.wchar_;
     import core.sys.windows.winbase;
     import core.sys.windows.winnls : CP_ACP;
     import core.sys.windows.winnt;
@@ -32,6 +40,7 @@ version (Windows)
 }
 else version (Posix)
 {
+    import core.sys.posix.dirent;
     import core.sys.posix.fcntl;
     import core.sys.posix.sys.mman;
     import core.sys.posix.sys.stat;
@@ -587,3 +596,163 @@ private auto ref fakePure(F)(scope F fun) pure
     mixin("alias PureFun = " ~ F.stringof ~ " pure;");
     return (cast(PureFun) fun)();
 }
+
+/***********************************
+ * Recursively search all the directories and files under dir_path
+ * for files that match one of the extensions in exts[].
+ * Pass the matches to sink.
+ * Params:
+ *      dir_path = root of directories to search
+ *      exts = array of filename extensions to match
+ *      recurse = go into subdirectories
+ *      filenameSink = accepts the resulting matches
+ * Returns:
+ *      true for failed to open the directory
+ */
+bool findFiles(const char* dir_path, const char[][] exts, bool recurse, void delegate(const(char)[]) nothrow filenameSink)
+{
+    enum log = false;
+    if (log) printf("findFiles() dir_path: %s\n", dir_path);
+    version (Windows)
+    {
+        debug
+            enum BufLength = 10;        // trigger any reallocation bugs
+        else
+            enum BufLength = 100;
+        char[BufLength + 1] buf = void;
+        char* fullPath = buf.ptr;
+        size_t fullPathLength = BufLength;
+
+        // fullPath = dir_path \ *.*
+        const dir_pathLength = strlen(dir_path);
+        auto count = dir_pathLength + 1 + 3;
+        if (count > fullPathLength)
+        {
+            fullPathLength = count;
+            fullPath = cast(char*)Mem.xrealloc_noscan(fullPath == buf.ptr ? null : fullPath, fullPathLength + 1);
+        }
+        memcpy(fullPath, dir_path, dir_pathLength);
+        strcpy(fullPath + dir_pathLength, "\\*.*".ptr);
+
+        if (log) printf("fullPath: %s\n", fullPath);
+
+        WIN32_FIND_DATAW ffd = void;
+        HANDLE hFind = fullPath[0 .. strlen(fullPath)].extendedPathThen!(p => FindFirstFileW(p.ptr, &ffd));
+        if (hFind == INVALID_HANDLE_VALUE)
+            return true;
+
+        do
+        {
+            if (log) wprintf("ffd.cFileName: %s\n", ffd.cFileName.ptr);
+            if (ffd.cFileName[0] == 0)
+                continue; // ignore
+
+            if (ffd.cFileName[0] == '.')
+                continue;           // ignore files that start with a ., also ignore . and .. directories
+
+            const(char)[] name = toNarrowStringz(ffd.cFileName[0 .. wcslen(ffd.cFileName.ptr)], null);
+            if (log) printf("name: %s\n", name.ptr);
+
+            // fullPath = dir_path \ name.ptr
+            count = dir_pathLength + 1 + name.length;
+            if (count > fullPathLength)
+            {
+                fullPathLength = count;
+                fullPath = cast(char*)Mem.xrealloc_noscan(fullPath == buf.ptr ? null : fullPath, fullPathLength + 1);
+            }
+            strcpy(fullPath + dir_pathLength + 1, name.ptr);
+
+            if (ffd.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY)
+            {
+                if (recurse)
+                    findFiles(fullPath, exts, recurse, filenameSink);
+            }
+            else
+            {
+                const(char)[] nameExt = FileName.ext(name);
+                foreach (ext; exts[])
+                {
+                    if (nameExt == ext)
+                    {
+                        if (log) printf("adding %s\n", fullPath);
+                        filenameSink(fullPath[0 .. count]);
+                    }
+                }
+            }
+            mem.xfree(cast(void*)name.ptr);
+
+        } while (FindNextFileW(hFind, &ffd) != 0);
+
+        if (fullPath != buf.ptr)
+            mem.xfree(fullPath);
+        FindClose(hFind);
+        if (log) printf("findFiles() exit\n");
+        return false;
+    }
+    else version (Posix)
+    {
+        DIR* dir = opendir(dir_path);
+        if (!dir)
+            return true;
+
+        debug
+            enum BufLength = 10;        // trigger any reallocation bugs
+        else
+            enum BufLength = 100;
+        char[BufLength + 1] buf = void;
+        char* fullPath = buf.ptr;
+        size_t fullPathLength = BufLength;
+
+        dirent* entry;
+        while ((entry = readdir(dir)) != null)
+        {
+            //printf("entry: %s\n", entry.d_name.ptr);
+            if (entry.d_name[0] == '.')
+                continue;           // ignore files that start with a .
+
+            // fullPath = dir_path / entry.d_name.ptr
+            const dir_pathLength = strlen(dir_path);
+            const count = dir_pathLength + 1 + strlen(entry.d_name.ptr);
+            if (count > fullPathLength)
+            {
+                fullPathLength = count;
+                fullPath = cast(char*)Mem.xrealloc_noscan(fullPath == buf.ptr ? null : fullPath, fullPathLength + 1);
+            }
+            memcpy(fullPath, dir_path, dir_pathLength);
+            fullPath[dir_pathLength] = '/';
+            strcpy(fullPath + dir_pathLength + 1, entry.d_name.ptr);
+
+            stat_t statbuf;
+            if (lstat(fullPath, &statbuf) == -1)
+                continue;
+
+            const(char)[] name = entry.d_name.ptr[0 .. strlen(entry.d_name.ptr)]; // convert to D string
+            if (!name.length)
+                continue; // ignore
+
+            if (S_ISDIR(statbuf.st_mode))
+            {
+                if (recurse && !(name == "." || name == ".."))
+                    findFiles(fullPath, exts, recurse, filenameSink);
+            }
+            else if (S_ISREG(statbuf.st_mode))
+            {
+                foreach (ext; exts)
+                {
+                    if (FileName.ext(name) == ext)
+                    {
+                        //printf("%s\n", fullPath);
+                        filenameSink(fullPath[0 .. count]);
+                    }
+                }
+            }
+        }
+
+        if (fullPath != buf.ptr)
+            mem.xfree(fullPath);
+        closedir(dir);
+        return false;
+    }
+    else
+        static assert(0);
+}