Add fallback if __crystal_raise_cast_failed is missing

Author: HertzDevil

src/compiler/crystal/codegen/codegen.cr

@@ -1494,7 +1494,7 @@ module Crystal
           cond cmp, matches_block, doesnt_match_block
 
           position_at_end doesnt_match_block
-          codegen_raise_cast_failed(type_id, to_type, node)
+          codegen_raise_cast_failed(last_value, type_id, obj_type, to_type, node)
 
           position_at_end matches_block
           @last = downcast last_value, resulting_type, obj_type, true
@@ -1504,6 +1504,28 @@ module Crystal
       false
     end
 
+    def type_cast_exception_call(from_type, to_type, node, var_name)
+      pieces = [
+        StringLiteral.new("Cast from ").at(node),
+        Call.new(Var.new(var_name).at(node), "class").at(node),
+        StringLiteral.new(" to #{to_type} failed").at(node),
+      ] of ASTNode
+
+      if location = node.location
+        pieces << StringLiteral.new(", at #{location.expanded_location}:#{location.line_number}").at(node)
+      end
+
+      ex = Call.new(Path.global("TypeCastError").at(node), "new", StringInterpolation.new(pieces).at(node)).at(node)
+      call = Call.global("raise", ex).at(node)
+      call = @program.normalize(call)
+
+      meta_vars = MetaVars.new
+      meta_vars[var_name] = MetaVar.new(var_name, type: from_type)
+      visitor = MainVisitor.new(@program, meta_vars)
+      @program.visit_main call, visitor: visitor
+      call
+    end
+
     def visit(node : NilableCast)
       request_value(node.obj)
 
@@ -1559,26 +1581,33 @@ module Crystal
       end
     end
 
-    def codegen_raise_cast_failed(type_id, to_type, node)
+    def codegen_raise_cast_failed(value, type_id, obj_type, to_type, node)
       location = node.location
       set_current_debug_location(location) if location && @debug.line_numbers?
 
-      func = crystal_raise_cast_failed_fun
-      call_args = [
-        cast_to_void_pointer(type_id_to_class_name(type_id)),
-        cast_to_void_pointer(build_string_constant(to_type.to_s)),
-        location ? cast_to_void_pointer(build_string_constant(location.expanded_location.to_s)) : llvm_context.void_pointer.null,
-      ] of LLVM::Value
-
-      if (rescue_block = @rescue_block)
-        invoke_out_block = new_block "invoke_out"
-        invoke func, call_args, invoke_out_block, rescue_block
-        position_at_end invoke_out_block
+      if func = crystal_raise_cast_failed_fun
+        call_args = [
+          cast_to_void_pointer(type_id_to_class_name(type_id)),
+          cast_to_void_pointer(build_string_constant(to_type.to_s)),
+          location ? cast_to_void_pointer(build_string_constant(location.expanded_location.to_s)) : llvm_context.void_pointer.null,
+        ] of LLVM::Value
+
+        if (rescue_block = @rescue_block)
+          invoke_out_block = new_block "invoke_out"
+          invoke func, call_args, invoke_out_block, rescue_block
+          position_at_end invoke_out_block
+        else
+          call func, call_args
+        end
+
+        unreachable
       else
-        call func, call_args
+        # fallback for stdlib before 1.16.2 when using a 1.16.2 or later compiler
+        temp_var_name = @program.new_temp_var_name
+        context.vars[temp_var_name] = LLVMVar.new(value, obj_type, already_loaded: true)
+        accept type_cast_exception_call(obj_type, to_type, node, temp_var_name)
+        context.vars.delete temp_var_name
       end
-
-      unreachable
     end
 
     def type_id_to_class_name(type_id)
@@ -2357,7 +2386,7 @@ module Crystal
       if raise_cast_failed_fun = @raise_cast_failed_fun
         check_main_fun RAISE_CAST_FAILED_NAME, raise_cast_failed_fun
       else
-        raise Error.new("Missing __crystal_raise_cast_failed function, either use std-lib's prelude or define it")
+        nil
       end
     end