Fix compilation error for lambdas in unused functions (#1016)

Previously, in certain cases, there could be a compilation error:
> var Lambda$ufa6f526451637135_0::$tmp_var is declared 
> but never written; please, provide a default value

compiler/pipes/check-classes.cpp

@@ -72,7 +72,6 @@ inline void CheckClassesPass::check_static_fields_inited(ClassPtr klass) {
 }
 
 inline void CheckClassesPass::check_instance_fields_inited(ClassPtr klass) {
-  // TODO KPHP-221: the old code is kept for now (check for Unknown)
   klass->members.for_each([](const ClassMemberInstanceField &f) {
     PrimitiveType ptype = f.var->tinf_node.get_type()->get_real_ptype();
     kphp_error(ptype != tp_any,

compiler/pipes/filter-only-actually-used.cpp

@@ -9,6 +9,78 @@
 #include "compiler/data/src-file.h"
 #include "compiler/compiler-core.h"
 #include "compiler/threading/profiler.h"
+#include "compiler/vertex-util.h"
+
+// having a typed callable __invoke(), which is a virtual function with switch-case dispatching,
+// replace body of `case {lambda_class_to_remove.hash()}:` (which is a lambda invoke call)
+// to just `break`; see below, why this is important
+class RemoveLambdaCallFromTypedCallablePass final : public FunctionPassBase {
+  std::string case_hash;
+
+public:
+  std::string get_description() override {
+    return "Remove lambda call from typed callable";
+  }
+
+  explicit RemoveLambdaCallFromTypedCallablePass(ClassPtr lambda_class_to_remove)
+    : case_hash(std::to_string(lambda_class_to_remove->get_hash())) {}
+
+  VertexPtr on_enter_vertex(VertexPtr root) override {
+    if (auto as_case = root.try_as<op_case>()) {
+      if (auto as_int_const = as_case->expr().try_as<op_int_const>()) {
+        if (as_int_const->str_val == case_hash) {
+          auto level1 = VertexUtil::create_int_const(1);
+          return VertexAdaptor<op_case>::create(as_int_const, VertexAdaptor<op_seq>::create(VertexAdaptor<op_break>::create(level1)));
+        }
+      }
+    }
+
+    return root;
+  }
+};
+
+// when a lambda with `use` statement (=> with an instance field) occurs inside unused function,
+// it still can be reachable from a typed callable __invoke(),
+// but its field types can't be inferred, they'll be left 'any' and trigger an error after
+// to prevent this, manually remove this lambda from that __invoke() body
+// as well as remove all lambda's mentions from used_functions
+class AnalyzeLambdasInUnusedFunctionPass final : public FunctionPassBase {
+  IdMap<FunctionPtr> &used_functions;
+
+public:
+  std::string get_description() override {
+    return "Analyze lambdas in unused function";
+  }
+
+  explicit AnalyzeLambdasInUnusedFunctionPass(IdMap<FunctionPtr> &used_functions)
+    : used_functions(used_functions) {}
+
+  VertexPtr on_enter_vertex(VertexPtr root) override {
+    if (auto as_call = root.try_as<op_func_call>();
+      as_call && as_call->func_id->class_id && as_call->func_id->class_id->is_lambda_class() && as_call->func_id->is_constructor()) {
+      ClassPtr lambda_class = as_call->func_id->class_id;
+      const ClassMemberInstanceMethod *m_invoke = lambda_class->members.get_instance_method("__invoke");
+      if (m_invoke && used_functions[m_invoke->function->outer_function]) {
+        // f_lambda occurs inside unused function, but is used; the only reason is it's used from a typed callable
+        FunctionPtr f_lambda = m_invoke->function->outer_function;
+        kphp_assert(lambda_class->implements.size() == 1 && lambda_class->implements[0]->is_typed_callable_interface());
+        FunctionPtr f_typed_invoke = lambda_class->implements[0]->members.get_instance_method("__invoke")->function;
+
+        RemoveLambdaCallFromTypedCallablePass pass(lambda_class);
+        run_function_pass(f_typed_invoke->root, &pass);
+
+        AnalyzeLambdasInUnusedFunctionPass self_pass(used_functions);
+        run_function_pass(f_lambda, &self_pass);
+
+        used_functions[f_lambda] = {};
+        used_functions[m_invoke->function] = {};
+        used_functions[lambda_class->construct_function] = {};
+      }
+    }
+
+    return root;
+  }
+};
 
 namespace {
 
@@ -261,6 +333,16 @@ void FilterOnlyActuallyUsedFunctionsF::on_finish(DataStream<FunctionPtr> &os) {
   remove_unused_class_methods(all, used_functions);
   stage::die_if_global_errors();
 
+  // remove lambdas from unused functions, see comments above
+  for (const auto &f_and_e : all) {
+    FunctionPtr fun = f_and_e.first;
+    if (fun->has_lambdas_inside && !fun->is_lambda() && !used_functions[fun]) {
+      AnalyzeLambdasInUnusedFunctionPass pass(used_functions);
+      run_function_pass(fun, &pass);
+    }
+  }
+  stage::die_if_global_errors();
+
   // forward the reachable functions into the data stream;
   // this should be the last step
   for (const auto &f : used_functions) {

compiler/pipes/generate-virtual-methods.cpp

@@ -422,10 +422,6 @@ void generate_body_of_virtual_method(FunctionPtr virtual_function) {
       cases.emplace_back(v_case);
     }
   }
-  if (!cases.empty()) {
-    auto case_default_warn = generate_critical_error_call(fmt_format("call method({}) on null object", virtual_function->as_human_readable(false)));
-    cases.emplace_back(VertexAdaptor<op_default>::create(VertexAdaptor<op_seq>::create(case_default_warn)));
-  }
 
   if (cases.empty() && !stage::has_error()) {
     // when there are no inheritors of an interface, generate an empty body if possible —
@@ -436,7 +432,7 @@ void generate_body_of_virtual_method(FunctionPtr virtual_function) {
     auto call_get_hash = VertexAdaptor<op_func_call>::create(ClassData::gen_vertex_this({}));
     call_get_hash->str_val = "get_hash_of_class";
     call_get_hash->func_id = G->get_function(call_get_hash->str_val);
-    virtual_function->root->cmd_ref() = VertexAdaptor<op_seq>::create(VertexUtil::create_switch_vertex(virtual_function, call_get_hash, std::move(cases)));
+    virtual_function->root->cmd_ref() = VertexAdaptor<op_seq>::create(VertexUtil::create_switch_vertex(virtual_function, call_get_hash, std::move(cases)), generate_critical_error_call(fmt_format("call method({}) on null object", virtual_function->as_human_readable(false))));
   }
 
   virtual_function->type = FunctionData::func_local;    // could be func_extern before, but now it has a body

tests/phpt/lambdas/020_uses_in_lambda.php

@@ -110,3 +110,64 @@ function l2_modif() {
 }
 (new WithFCapturingDeep)->l2();
 (new WithFCapturingDeep)->l2_modif();
+
+class Example020 {
+  static private function takeInt(int $i) { echo $i; }
+
+  public function unused_function(): void {
+    $tmp_var = "";
+    $this->call_function(function() use ($tmp_var): void {});
+    $int = 10;
+    $this->call_function(function() use ($int): void { self::takeInt($int); });
+  }
+
+  /** @param callable():void $fn */
+  public function call_function(callable $fn): void {
+    $fn();
+  }
+}
+
+(new Example020())->call_function(function(): void {});
+
+class Bxample020 {
+  /**
+   * @param callable(int):int $fn
+   */
+  public function unused_function(callable $fn): int {
+    return $this->test2(function () use ($fn) {
+      return $fn(1);
+    });
+  }
+
+  /**
+   * @param callable():int $fn
+   */
+  public function test2(callable $fn): int {
+    return $fn();
+  }
+}
+
+$bxample = new Bxample020();
+$bxample->test2(function() { return 0; });
+
+
+class Cxample {
+  public function unused_function(): void {
+    $tmp_var = "";
+    $this->call_function_first(function() use ($tmp_var): void {
+      $this->call_function_second(function() use ($tmp_var) {});
+    });
+  }
+
+  /** @param callable():void $fn */
+  public function call_function_first(callable $fn): void {
+    $fn();
+  }
+
+  /** @param callable():void $fn */
+  public function call_function_second(callable $fn): void {
+    $fn();
+  }
+}
+
+(new Cxample)->call_function_first(function():void{} );