drop extra arguments for compiled internal functions

src/Utils/PartiallyAppliedFunction.php

@@ -66,17 +66,26 @@ class PartiallyAppliedFunction implements Decorator, Compilable
         return $this->callable;
     }
 
+    /**
+     * Internal functions throw when given too many arguments, so for a non-variadic internal target the compiled
+     * closure drops trailing arguments past its parameter count (e.g. the key passed by collection functions).
+     */
     public function compile(): \Closure
     {
         $callable     = compile($this->callable);
         $arguments    = $this->arguments;
         $placeholders = array_keys($arguments, PLACEHOLDER, true);
 
+        $target = new \ReflectionFunction($callable);
+        $extra  = $target->isInternal() && !$target->isVariadic()
+            ? max(0, $target->getNumberOfParameters() - count($arguments))
+            : null;
+
         if (empty($placeholders)) {
-            return static fn (...$args) => $callable(...$arguments, ...array_values($args));
+            return static fn (...$args) => $callable(...$arguments, ...array_slice(array_values($args), 0, $extra));
         }
 
-        return static function (...$args) use ($callable, $arguments, $placeholders) {
+        return static function (...$args) use ($callable, $arguments, $placeholders, $extra) {
             $args  = array_values($args);
             $count = min(count($placeholders), count($args));
 
@@ -84,7 +93,7 @@ class PartiallyAppliedFunction implements Decorator, Compilable
                 $arguments[$placeholders[$i]] = $args[$i];
             }
 
-            return $callable(...$arguments, ...array_slice($args, $count));
+            return $callable(...$arguments, ...array_slice($args, $count, $extra));
         };
     }
 

tests/Collections/CallbackTest.php

@@ -38,6 +38,11 @@ class CallbackTest extends \PHPUnit\Framework\TestCase
         $this->assertSame(['v', 'k'], callback(fn (...$args) => $args)('v', 'k'));
     }
 
+    public function testPartialOfInternalFunctionDoesNotGetKey()
+    {
+        $this->assertSame('a', callback(f\partial(trim(...), _, 'x'))('xax', 'key'));
+    }
+
     public function testDecoratorIsCompiled()
     {
         $callback = callback(f\partial(fn ($prefix, $v, $k) => "$prefix$k=$v", '>'));

tests/CompileTest.php

@@ -88,6 +88,21 @@ class CompileTest extends \PHPUnit\Framework\TestCase
         $this->assertSame($partial(), f\compile($partial)());
     }
 
+    public function testCompileDropsExtraArgumentsForInternalTarget()
+    {
+        $this->assertSame('aa', f\compile(f\partial(str_repeat(...), _, 2))('a', 'extra'));
+    }
+
+    public function testCompileKeepsExtraArgumentsForVariadicInternalTarget()
+    {
+        $this->assertSame(['a', 'b', 'c'], f\compile(f\partial(array_merge(...), ['a']))(['b'], ['c']));
+    }
+
+    public function testCompileDropsExtraArgumentsForCurriedInternalTarget()
+    {
+        $this->assertSame('aa', f\compile(f\curry(str_repeat(...), null, 'a'))(2, 'extra'));
+    }
+
     public function testCompileFunctionDelegatesToMethod()
     {
         $partial = f\partial(str_replace(...), 'a', _, 'banana');