allow statically linking librocksdb (#29)

README.md

@@ -20,6 +20,16 @@ A RocksDB installation that provides `librocksdb.so`. This means that on Debian,
 
 See [simple_example](examples/simple_example.nim)
 
+### Static linking
+
+To statically link librocksdb, you would do something like:
+
+```nim
+nim c -d:LibrocksbStaticArgs='-l:librocksdb.a' --gcc.linkerexe=g++ --threads:on your_program.nim
+```
+
+(we need the C++ linker profile because it's a C++ library)
+
 ## Future directions
 
 In the future, Nim-RocksDB might provide a high-level API that:

rocksdb.nimble

@@ -4,6 +4,7 @@ author        = "Status Research & Development GmbH"
 description   = "A wrapper for Facebook's RocksDB, an embeddable, persistent key-value store for fast storage"
 license       = "Apache License 2.0 or GPLv2"
 skipDirs      = @["examples", "tests"]
+mode          = ScriptMode.Verbose
 
 ### Dependencies
 requires "nim >= 1.2.0",
@@ -18,4 +19,7 @@ proc test(args, path: string) =
 
 task test, "Run tests":
   test "", "tests/all.nim"
+  # Too troublesome to install "librocksdb.a" in CI, but this is how we would
+  # test it (we need the C++ linker profile because it's a C++ library):
+  # test "-d:LibrocksbStaticArgs='-l:librocksdb.a' --gcc.linkerexe=g++", "tests/all.nim"
 

rocksdb/librocksdb.nim

@@ -1,5 +1,4 @@
-# Nim-RocksDB
-# Copyright 2018 Status Research & Development GmbH
+# Copyright 2018-2022 Status Research & Development GmbH
 # Licensed under either of
 #
 #  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
@@ -48,6 +47,8 @@ proc shouldUseNativeLinking(): bool {.compileTime.} =
   when defined(linux):
     return true
 
+const LibrocksbStaticArgs {.strdefine.}: string = ""
+
 template rocksType(T) =
   type T* = distinct pointer
   proc isNil*(v: T): bool {.borrow, gcsafe.}
@@ -100,10 +101,14 @@ rocksType rocksdb_transaction_t
 rocksType rocksdb_checkpoint_t
 
 ##  DB operations
-when shouldUseNativeLinking():
+when LibrocksbStaticArgs != "":
+  {.pragma: importrocks, importc, cdecl.}
+  {.passL: LibrocksbStaticArgs.}
+else:
+  when shouldUseNativeLinking():
     {.pragma: importrocks, importc, cdecl.}
     {.passL: "-lrocksdb".}
-else:
+  else:
     {.pragma: importrocks, importc, cdecl, dynlib: librocksdb.}
 
 proc rocksdb_open*(options: rocksdb_options_t; name: cstring; errptr: ptr cstring): rocksdb_t {.importrocks.}