Interpreter: cast proc call arguments to proc arg types

spec/compiler/interpreter/procs_spec.cr

@@ -70,4 +70,34 @@ describe Crystal::Repl::Interpreter do
         CODE
     end
   end
+
+  it "casts proc call arguments to proc arg types (#12350)" do
+    interpret(<<-CODE).should eq(42)
+      abstract struct Base
+      end
+
+      struct Foo < Base
+        def initialize(@x : Int32)
+        end
+
+        def x
+          @x
+        end
+      end
+
+      struct Bar < Base
+      end
+
+      proc = ->(base : Base) {
+        if base.is_a?(Foo)
+          base.x
+        else
+          0
+        end
+      }
+
+      bar = Foo.new(42)
+      proc.call(bar)
+    CODE
+  end
 end

src/compiler/crystal/interpreter/compiler.cr

@@ -1796,7 +1796,7 @@ class Crystal::Repl::Compiler < Crystal::Visitor
 
     body = target_def.body
     if body.is_a?(Primitive)
-      visit_primitive(node, body)
+      visit_primitive(node, body, target_def)
       return false
     end
 

src/compiler/crystal/interpreter/primitives.cr

@@ -6,7 +6,7 @@ require "./compiler"
 # (for example `caller`, or doing a fiber context switch.)
 
 class Crystal::Repl::Compiler
-  private def visit_primitive(node, body, wants_struct_pointer = false)
+  private def visit_primitive(node, body, target_def)
     obj = node.obj
 
     case body.name
@@ -254,7 +254,19 @@ class Crystal::Repl::Compiler
 
       pointer_address(node: node)
     when "proc_call"
-      node.args.each { |arg| request_value(arg) }
+      proc_type = (obj.try(&.type) || scope).as(ProcInstanceType)
+
+      node.args.each_with_index do |arg, arg_index|
+        request_value(arg)
+
+        # Cast call argument to proc's type
+        # (this same logic is done in codegen/primtiives.cr)
+        proc_arg_type = proc_type.arg_types[arg_index]
+        target_def_arg_type = target_def.args[arg_index].type
+        if proc_arg_type != target_def_arg_type
+          upcast(arg, target_def_arg_type, proc_arg_type)
+        end
+      end
 
       obj ? request_value(obj) : put_self(node: node)