Compiler: improve error message when guessing variable as Nil. Fixes #…

…3232
crystal-lang · Sep 3, 2016 · eceb2d8 · eceb2d8
1 parent 11cf844
commit eceb2d8
Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/spec/compiler/semantic/instance_var_spec.cr b/spec/compiler/semantic/instance_var_spec.cr
@@ -2851,7 +2851,7 @@ describe "Semantic: instance var" do
 
       Foo.new.x
       ),
-      "Can't infer the type of instance variable '@x' of Foo"
+      "instance variable @x of Foo was inferred to be Nil, but Nil alone provides no information"
   end
 
   it "says can't infer type if only nil was assigned, in generic type" do
@@ -2868,7 +2868,7 @@ describe "Semantic: instance var" do
 
       Foo(Int32).new.x
       ),
-      "Can't infer the type of instance variable '@x' of Foo"
+      "instance variable @x of Foo(T) was inferred to be Nil, but Nil alone provides no information"
   end
 
   it "allows nil instance var because it's a generic type" do

diff --git a/src/compiler/crystal/semantic/type_declaration_processor.cr b/src/compiler/crystal/semantic/type_declaration_processor.cr
@@ -323,7 +323,7 @@ struct Crystal::TypeDeclarationProcessor
       # Nil is not useful and is the same as not having it at all, at
       # least for non-generic types)
       if type.nil_type?
-        return
+        raise_nil_instance_var owner, name, type_info.location
       end
 
       declare_meta_type_var(owner.instance_vars, owner, name, type, type_info.location, instance_var: true)
@@ -352,7 +352,7 @@ struct Crystal::TypeDeclarationProcessor
 
       # Same as above, only Nil makes no sense
       if type.nil_type?
-        return
+        raise_nil_instance_var owner, name, type_info.location
       end
 
       declare_meta_type_var(owner.instance_vars, owner, name, type, type_info.location, instance_var: true)
@@ -383,6 +383,10 @@ struct Crystal::TypeDeclarationProcessor
     !non_nilable_vars || (non_nilable_vars && !non_nilable_vars.includes?(name))
   end
 
+  private def raise_nil_instance_var(owner, name, location)
+    raise TypeException.new("instance variable #{name} of #{owner} was inferred to be Nil, but Nil alone provides no information", location)
+  end
+
   private def compute_non_nilable_instance_vars
     owners = sort_types_by_depth(@initialize_infos.keys).uniq!