From b598255f74694e3c663ca0c85696f7dcb5f6f0f7 Mon Sep 17 00:00:00 2001
From: Ivan FB <ivansete@status.im>
Date: Mon, 11 May 2026 22:39:41 +0200
Subject: [PATCH] =?UTF-8?q?fix=20Lib-name=20derivation=20breaks=20on=20nam?=
 =?UTF-8?q?es=20with=20underscores=20(rust.nim:54,=20cpp.nim:38=E2=80=9342?=
 =?UTF-8?q?).=20parts[0]=20of=20nim=5Ftimer=5Fcreate=20is=20"nim",=20not?=
 =?UTF-8?q?=20"nim=5Ftimer".=20The=20example=20library=20happens=20to=20be?=
 =?UTF-8?q?=20=20=20=20nimtimer,=20so=20this=20never=20bites.=20The=20curr?=
 =?UTF-8?q?entLibName=20short-circuit=20covers=20the=20registered=20case,?=
 =?UTF-8?q?=20but=20the=20fallback=20path=20is=20wrong,=20and=20silent.?=
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Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 ffi/codegen/rust.nim       | 42 ++++++++++++++------------------------
 ffi/internal/ffi_macro.nim |  7 +++++++
 2 files changed, 22 insertions(+), 27 deletions(-)

diff --git a/ffi/codegen/rust.nim b/ffi/codegen/rust.nim
index 0e17b77..98cbdfc 100644
--- a/ffi/codegen/rust.nim
+++ b/ffi/codegen/rust.nim
@@ -43,17 +43,13 @@ proc nimTypeToRust*(typeName: string): string =
   else: toPascalCase(t)
 
 proc deriveLibName*(procs: seq[FFIProcMeta]): string =
-  ## Extracts the common prefix before the first `_` from proc names.
-  ## e.g. ["nimtimer_create", "nimtimer_echo"] → "nimtimer"
-  if currentLibName.len > 0:
-    return currentLibName
-  if procs.len == 0:
-    return "unknown"
-  let first = procs[0].procName
-  let parts = first.split('_')
-  if parts.len > 0:
-    return parts[0]
-  return "unknown"
+  ## Returns the library name registered by declareLibrary("<name>", T).
+  ## Caller must guarantee currentLibName is set (genBindings errors otherwise);
+  ## there is no sound heuristic to recover it from proc names alone --
+  ## "nim_timer_create" is ambiguous between "nim" and "nim_timer".
+  doAssert currentLibName.len > 0,
+    "deriveLibName called before declareLibrary; this is an internal bug"
+  currentLibName
 
 proc stripLibPrefix*(procName: string, libName: string): string =
   ## Strips the library prefix from a proc name.
@@ -178,22 +174,14 @@ proc generateFfiRs*(procs: seq[FFIProcMeta]): string =
   lines.add(");")
   lines.add("")
 
-  # Collect unique lib names for #[link(...)]
-  var libNames: seq[string] = @[]
-  for p in procs:
-    if p.libName notin libNames:
-      libNames.add(p.libName)
-
-  # Derive lib name from proc names if not set
-  var linkLibName = ""
-  if libNames.len > 0 and libNames[0].len > 0:
-    linkLibName = libNames[0]
-  else:
-    # derive from first proc name
-    if procs.len > 0:
-      let parts = procs[0].procName.split('_')
-      if parts.len > 0:
-        linkLibName = parts[0]
+  # Lib name for #[link(...)]. The macro bakes `libName: currentLibName` into
+  # every proc meta at registration time; if the registry has procs at all,
+  # they all share the same libName. No heuristic fallback -- genBindings()
+  # enforces that declareLibrary() was called.
+  doAssert procs.len > 0, "generateFfiRs called with empty proc registry"
+  let linkLibName = procs[0].libName
+  doAssert linkLibName.len > 0,
+    "proc meta missing libName; this is an internal bug (declareLibrary unset?)"
 
   lines.add("#[link(name = \"$1\")]" % [linkLibName])
   lines.add("extern \"C\" {")
diff --git a/ffi/internal/ffi_macro.nim b/ffi/internal/ffi_macro.nim
index efa4c5b..464644c 100644
--- a/ffi/internal/ffi_macro.nim
+++ b/ffi/internal/ffi_macro.nim
@@ -1634,6 +1634,13 @@ macro genBindings*(
         "genBindings: output directory is empty." &
         " Pass it as an argument or set -d:ffiOutputDir=path/to/output"
       )
+    if currentLibName.len == 0:
+      error(
+        "genBindings: library name is empty. Call declareLibrary(\"<name>\", <T>)" &
+        " BEFORE any {.ffi.} / {.ffiCtor.} annotations so the library name is" &
+        " registered. The library name cannot be safely derived from proc names" &
+        " (e.g. \"nim_timer_create\" is ambiguous between \"nim\" and \"nim_timer\")."
+      )
     let lang = targetLang.toLowerAscii()
     let libName = deriveLibName(ffiProcRegistry)
     case lang