fix Hardcoded Nim build flags in generated build files. build.rs and CMakeLists.txt both bake in --mm:orc and -d:chronicles_log_level=WARN (rust.nim:121–122, cpp.nim:463–464).

The whole point of a generic generator is decoupling — this couples every consumer of nim-ffi to one specific project's Nim build conventions. Plumb these through
  genBindings() parameters or a config block.

examples/nim_timer/nim_timer.nimble

@@ -11,6 +11,8 @@ requires "taskpools"
 requires "https://github.com/logos-messaging/nim-ffi >= 0.1.3"
 
 const nimFlags = "--mm:orc -d:chronicles_log_level=WARN"
+# Flags baked into the generated build.rs / CMakeLists.txt -- see ffi.nimble.
+const genBakedFlags = "--mm:orc -d:chronicles_log_level=WARN"
 
 task build, "Compile the nimtimer library":
   exec "nim c " & nimFlags &
@@ -19,9 +21,13 @@ task build, "Compile the nimtimer library":
 task genbindings_rust, "Generate Rust bindings for the nimtimer example":
   exec "nim c " & nimFlags & " --app:lib --noMain --nimMainPrefix:libnimtimer" &
     " -d:ffiGenBindings -d:targetLang=rust" & " -d:ffiOutputDir=rust_bindings" &
-    " -d:ffiNimSrcRelPath=nim_timer.nim" & " -o:/dev/null nim_timer.nim"
+    " -d:ffiNimSrcRelPath=nim_timer.nim" &
+    " -d:ffiNimBuildFlags=\"" & genBakedFlags & "\"" &
+    " -o:/dev/null nim_timer.nim"
 
 task genbindings_cpp, "Generate C++ bindings for the nimtimer example":
   exec "nim c " & nimFlags & " --app:lib --noMain --nimMainPrefix:libnimtimer" &
     " -d:ffiGenBindings -d:targetLang=cpp" & " -d:ffiOutputDir=cpp_bindings" &
-    " -d:ffiNimSrcRelPath=nim_timer.nim" & " -o:/dev/null nim_timer.nim"
+    " -d:ffiNimSrcRelPath=nim_timer.nim" &
+    " -d:ffiNimBuildFlags=\"" & genBakedFlags & "\"" &
+    " -o:/dev/null nim_timer.nim"

ffi.nimble

@@ -41,18 +41,26 @@ task genbindings_example, "Generate Rust bindings for the nim_timer example":
   exec "nim c " & nimFlagsOrc & " --app:lib --noMain --nimMainPrefix:libnimtimer -d:ffiGenBindings -o:/dev/null examples/nim_timer/nim_timer.nim"
   exec "nim c " & nimFlagsRefc & " --app:lib --noMain --nimMainPrefix:libnimtimer -d:ffiGenBindings -o:/dev/null examples/nim_timer/nim_timer.nim"
 
+# Flags baked into the generated build.rs / CMakeLists.txt so downstream
+# consumers compile the Nim library with the same conventions this example
+# uses. Anything that should NOT be hardcoded into the published bindings
+# goes here, not in the generator.
+const genBakedFlags = "--mm:orc -d:chronicles_log_level=WARN"
+
 task genbindings_rust, "Generate Rust bindings for the nim_timer example":
   exec "nim c " & nimFlagsOrc &
     " --app:lib --noMain --nimMainPrefix:libnimtimer" &
     " -d:ffiGenBindings -d:targetLang=rust" &
     " -d:ffiOutputDir=examples/nim_timer/rust_bindings" &
     " -d:ffiNimSrcRelPath=../nim_timer.nim" &
+    " -d:ffiNimBuildFlags=\"" & genBakedFlags & "\"" &
     " -o:/dev/null examples/nim_timer/nim_timer.nim"
   exec "nim c " & nimFlagsRefc &
     " --app:lib --noMain --nimMainPrefix:libnimtimer" &
     " -d:ffiGenBindings -d:targetLang=rust" &
     " -d:ffiOutputDir=examples/nim_timer/rust_bindings" &
     " -d:ffiNimSrcRelPath=../nim_timer.nim" &
+    " -d:ffiNimBuildFlags=\"" & genBakedFlags & "\"" &
     " -o:/dev/null examples/nim_timer/nim_timer.nim"
 
 task genbindings_cpp, "Generate C++ bindings for the nim_timer example":
@@ -61,10 +69,12 @@ task genbindings_cpp, "Generate C++ bindings for the nim_timer example":
     " -d:ffiGenBindings -d:targetLang=cpp" &
     " -d:ffiOutputDir=examples/nim_timer/cpp_bindings" &
     " -d:ffiNimSrcRelPath=../nim_timer.nim" &
+    " -d:ffiNimBuildFlags=\"" & genBakedFlags & "\"" &
     " -o:/dev/null examples/nim_timer/nim_timer.nim"
   exec "nim c " & nimFlagsRefc &
     " --app:lib --noMain --nimMainPrefix:libnimtimer" &
     " -d:ffiGenBindings -d:targetLang=cpp" &
     " -d:ffiOutputDir=examples/nim_timer/cpp_bindings" &
     " -d:ffiNimSrcRelPath=../nim_timer.nim" &
+    " -d:ffiNimBuildFlags=\"" & genBakedFlags & "\"" &
     " -o:/dev/null examples/nim_timer/nim_timer.nim"

ffi/codegen/cpp.nim

@@ -483,10 +483,15 @@ proc generateCppHeader*(
 
   result = lines.join("\n")
 
-proc generateCppCMakeLists*(libName: string, nimSrcRelPath: string): string =
+proc generateCppCMakeLists*(
+    libName: string, nimSrcRelPath: string, nimBuildFlags: string = ""
+): string =
   ## Generates CMakeLists.txt for the C++ bindings directory.
   ## CMake uses ${...} which would clash with Nim's % format operator,
   ## so we build the file line by line using string concatenation.
+  ## nimBuildFlags is a whitespace-separated string of extra `nim c` flags
+  ## injected after `nim c` and before the required --app:lib / --noMain /
+  ## --nimMainPrefix / -o: flags.
   let src = nimSrcRelPath.replace("\\", "/")
   let cv = "${CMAKE_CURRENT_SOURCE_DIR}" # CMake variable shorthand
   let rv = "${REPO_ROOT}"
@@ -554,8 +559,8 @@ proc generateCppCMakeLists*(libName: string, nimSrcRelPath: string): string =
   L.add("add_custom_command(")
   L.add("    OUTPUT  \"" & lf & "\"")
   L.add("    COMMAND \"" & nm & "\" c")
-  L.add("                --mm:orc")
-  L.add("                -d:chronicles_log_level=WARN")
+  for tok in nimBuildFlags.splitWhitespace():
+    L.add("                " & tok)
   L.add("                --app:lib")
   L.add("                --noMain")
   L.add("                \"--nimMainPrefix:lib" & libName & "\"")
@@ -601,7 +606,11 @@ proc generateCppBindings*(
     libName: string,
     outputDir: string,
     nimSrcRelPath: string,
+    nimBuildFlags: string = "",
 ) =
   createDir(outputDir)
   writeFile(outputDir / (libName & ".hpp"), generateCppHeader(procs, types, libName))
-  writeFile(outputDir / "CMakeLists.txt", generateCppCMakeLists(libName, nimSrcRelPath))
+  writeFile(
+    outputDir / "CMakeLists.txt",
+    generateCppCMakeLists(libName, nimSrcRelPath, nimBuildFlags),
+  )

ffi/codegen/meta.nim

@@ -44,3 +44,11 @@ const ffiOutputDir* {.strdefine.} = ""
 # Nim source path (relative to outputDir) embedded in generated build files;
 # set with -d:ffiNimSrcRelPath=../relative/path.nim
 const ffiNimSrcRelPath* {.strdefine.} = ""
+
+# Whitespace-separated extra Nim compiler flags to bake into the generated
+# build.rs / CMakeLists.txt for the project's own `nim c` invocation. The
+# generator emits only the strictly-required flags (--app:lib, --noMain,
+# --nimMainPrefix, -o:) by default; everything else (gc choice, log level,
+# project-specific -d defines, etc.) is up to the caller. Example:
+#   -d:ffiNimBuildFlags="--mm:orc -d:chronicles_log_level=WARN"
+const ffiNimBuildFlags* {.strdefine.} = ""

ffi/codegen/rust.nim

@@ -81,10 +81,27 @@ tokio = { version = "1", features = ["sync"] }
 """ %
     [libName]
 
-proc generateBuildRs*(libName: string, nimSrcRelPath: string): string =
+proc rustEscapeStrLit(s: string): string =
+  ## Escapes a string for safe embedding in a Rust string literal.
+  s.replace("\\", "\\\\").replace("\"", "\\\"")
+
+proc generateBuildRs*(
+    libName: string, nimSrcRelPath: string, nimBuildFlags: string = ""
+): string =
   ## Generates build.rs that compiles the Nim library.
   ## nimSrcRelPath is relative to the output (crate) directory.
+  ## nimBuildFlags is a whitespace-separated string of extra `nim c` flags
+  ## (e.g. "--mm:orc -d:chronicles_log_level=WARN") to inject into the
+  ## generated `nim c` invocation, after `nim c` and before the required
+  ## --app:lib / --noMain / --nimMainPrefix / -o: flags.
   let escapedSrc = nimSrcRelPath.replace("\\", "\\\\")
+  # Build the leading section of the cmd.arg(...) chain: the mandatory
+  # `.arg("c")` plus one `.arg("...")` per caller-supplied flag, each on its
+  # own line. The template then reads as `cmd$3` -- $3 is the whole leading
+  # chain, so no placeholder ever sits inside a method-call expression.
+  var argChain = ".arg(\"c\")"
+  for tok in nimBuildFlags.splitWhitespace():
+    argChain.add("\n        .arg(\"" & rustEscapeStrLit(tok) & "\")")
   result =
     """use std::path::PathBuf;
 use std::process::Command;
@@ -123,9 +140,7 @@ fn main() {
     compile_error!("nim-ffi build.rs: unsupported target OS (expected macos, linux, or windows)");
 
     let mut cmd = Command::new("nim");
-    cmd.arg("c")
-        .arg("--mm:orc")
-        .arg("-d:chronicles_log_level=WARN")
+    cmd$3
         .arg("--app:lib")
         .arg("--noMain")
         .arg(format!("--nimMainPrefix:lib$2"))
@@ -140,7 +155,7 @@ fn main() {
     println!("cargo:rerun-if-changed={}", nim_src.display());
 }
 """ %
-    [escapedSrc, libName]
+    [escapedSrc, libName, argChain]
 
 proc generateLibRs*(): string =
   result = """mod ffi;
@@ -502,13 +517,17 @@ proc generateRustCrate*(
     libName: string,
     outputDir: string,
     nimSrcRelPath: string,
+    nimBuildFlags: string = "",
 ) =
   ## Generates a complete Rust crate in outputDir.
   createDir(outputDir)
   createDir(outputDir / "src")
 
   writeFile(outputDir / "Cargo.toml", generateCargoToml(libName))
-  writeFile(outputDir / "build.rs", generateBuildRs(libName, nimSrcRelPath))
+  writeFile(
+    outputDir / "build.rs",
+    generateBuildRs(libName, nimSrcRelPath, nimBuildFlags),
+  )
   writeFile(outputDir / "src" / "lib.rs", generateLibRs())
   writeFile(outputDir / "src" / "ffi.rs", generateFfiRs(procs))
   writeFile(outputDir / "src" / "types.rs", generateTypesRs(types))

ffi/internal/ffi_macro.nim

@@ -1604,6 +1604,7 @@ macro ffiDtor*(prc: untyped): untyped =
 macro genBindings*(
     outputDir: static[string] = ffiOutputDir,
     nimSrcRelPath: static[string] = ffiNimSrcRelPath,
+    nimBuildFlags: static[string] = ffiNimBuildFlags,
 ): untyped =
   ## Emits C++ or Rust binding files from the compile-time FFI registries.
   ##
@@ -1638,11 +1639,13 @@ macro genBindings*(
     case lang
     of "rust":
       generateRustCrate(
-        ffiProcRegistry, ffiTypeRegistry, libName, outputDir, nimSrcRelPath
+        ffiProcRegistry, ffiTypeRegistry, libName, outputDir, nimSrcRelPath,
+        nimBuildFlags,
       )
     of "cpp", "c++":
       generateCppBindings(
-        ffiProcRegistry, ffiTypeRegistry, libName, outputDir, nimSrcRelPath
+        ffiProcRegistry, ffiTypeRegistry, libName, outputDir, nimSrcRelPath,
+        nimBuildFlags,
       )
     else:
       error("genBindings: unknown targetLang '" & lang & "'. Use 'rust' or 'cpp'.")