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[ffigen] Improve error message when native functions fail to load (Fixes #2953) #2981

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[ffigen] Improve error message when native functions fail to load (Fixes #2953) #2981

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5bba8cb
Fixed [ffigen] Better errors when native functions don't load #2953
singlakinjal Jan 19, 2026
9c67aed
Merge branch 'main' into fix-lookup-error
singlakinjal Jan 19, 2026
83f10b1
Merge branch 'main' into fix-lookup-error
singlakinjal Jan 22, 2026
5103ef3
Merge branch 'main' into fix-lookup-error
singlakinjal Jan 23, 2026
3811b4d
Handle missing Objective-C block bindings
singlakinjal Jan 23, 2026
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57 changes: 47 additions & 10 deletions pkgs/ffigen/example/simple/generated_bindings.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -24,19 +24,35 @@ class NativeLibrary {
return _sum(a, b);
}

late final _sumPtr =
_lookup<ffi.NativeFunction<ffi.Int Function(ffi.Int, ffi.Int)>>('sum');
late final _sumPtr = () {
try {
return _lookup<ffi.NativeFunction<ffi.Int Function(ffi.Int, ffi.Int)>>(
'sum',
);
} catch (e) {
throw ArgumentError(
"Failed to look up symbol 'sum'. This is likely because the native library is not linked or the symbol is missing. Error: $e",
);
}
}();
late final _sum = _sumPtr.asFunction<int Function(int, int)>();

/// Subtracts 2 integers.
int subtract(ffi.Pointer<ffi.Int> a, int b) {
return _subtract(a, b);
}

late final _subtractPtr =
_lookup<
late final _subtractPtr = () {
try {
return _lookup<
ffi.NativeFunction<ffi.Int Function(ffi.Pointer<ffi.Int>, ffi.Int)>
>('subtract');
} catch (e) {
throw ArgumentError(
"Failed to look up symbol 'subtract'. This is likely because the native library is not linked or the symbol is missing. Error: $e",
);
}
}();
late final _subtract = _subtractPtr
.asFunction<int Function(ffi.Pointer<ffi.Int>, int)>();

Expand All @@ -45,10 +61,17 @@ class NativeLibrary {
return _multiply(a, b);
}

late final _multiplyPtr =
_lookup<
late final _multiplyPtr = () {
try {
return _lookup<
ffi.NativeFunction<ffi.Pointer<ffi.Int> Function(ffi.Int, ffi.Int)>
>('multiply');
} catch (e) {
throw ArgumentError(
"Failed to look up symbol 'multiply'. This is likely because the native library is not linked or the symbol is missing. Error: $e",
);
}
}();
late final _multiply = _multiplyPtr
.asFunction<ffi.Pointer<ffi.Int> Function(int, int)>();

Expand All @@ -57,10 +80,17 @@ class NativeLibrary {
return _divide(a, b);
}

late final _dividePtr =
_lookup<
late final _dividePtr = () {
try {
return _lookup<
ffi.NativeFunction<ffi.Pointer<ffi.Float> Function(ffi.Int, ffi.Int)>
>('divide');
} catch (e) {
throw ArgumentError(
"Failed to look up symbol 'divide'. This is likely because the native library is not linked or the symbol is missing. Error: $e",
);
}
}();
late final _divide = _dividePtr
.asFunction<ffi.Pointer<ffi.Float> Function(int, int)>();

Expand All @@ -72,15 +102,22 @@ class NativeLibrary {
return _dividePrecision(a, b);
}

late final _dividePrecisionPtr =
_lookup<
late final _dividePrecisionPtr = () {
try {
return _lookup<
ffi.NativeFunction<
ffi.Pointer<ffi.Double> Function(
ffi.Pointer<ffi.Float>,
ffi.Pointer<ffi.Float>,
)
>
>('dividePrecision');
} catch (e) {
throw ArgumentError(
"Failed to look up symbol 'dividePrecision'. This is likely because the native library is not linked or the symbol is missing. Error: $e",
);
}
}();
late final _dividePrecision = _dividePrecisionPtr
.asFunction<
ffi.Pointer<ffi.Double> Function(
Expand Down
10 changes: 8 additions & 2 deletions pkgs/ffigen/lib/src/code_generator/func.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -208,8 +208,14 @@ $dartReturnType $enclosingFuncName($dartArgDeclString) {
final lookupStr = Namer.stringLiteral(lookupName);
final lookupFn = context.extraSymbols.lookupFuncName!.name;
s.write('''
late final $funcPointerName = $lookupFn<
${context.libs.prefix(ffiImport)}.NativeFunction<$cType>>('$lookupStr');
late final $funcPointerName = () {
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@liamappelbe liamappelbe Jan 19, 2026

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The main error message I wanted to improve is in objc_block.dart. In that file you can see a section that generates ObjC code containing native trampolines. That file also contains generated Dart code that tries to load those trampolines. That's the load that we need to check, and if it fails, tell the user that they need to include the .m file in their build (include the file name in the error).

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@liamappelbe liamappelbe Jan 27, 2026

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Only guard the loads in objc_block.dart. As Daco points out, the try-catch here is a bit redundant.

try {
return $lookupFn<
${context.libs.prefix(ffiImport)}.NativeFunction<$cType>>('$lookupStr');
} catch (e) {
throw ArgumentError("Failed to look up symbol '$lookupStr'. This is likely because the native library is not linked or the symbol is missing. Error: \$e");
}
}();
late final $funcVarName = $funcPointerName.asFunction<$dartType>($isLeafString);

''');
Expand Down