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Types not inferred properly for fields on record overrides #6303

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vicuna opened this Issue Jan 22, 2014 · 2 comments

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vicuna commented Jan 22, 2014

Original bug ID: 6303
Reporter: @alainfrisch
Assigned to: @garrigue
Status: closed (set by @xavierleroy on 2015-12-11T18:25:37Z)
Resolution: fixed
Priority: normal
Severity: major
Fixed in version: 4.02.0+dev
Category: typing
Monitored by: @gasche jmeber @hcarty

Bug description

On trunk, it seems that an expression {e with x = ...} does not propagate type constraints from x to the record type. The following code segfaults:

type 'a foo = {x: 'a; y: int}
let r = {{x = 0; y = 0} with x = 0}
let () = print_endline (r.x ^ "")

The type inferred for [r] is a polymorphic ['a foo], instead of [int foo].

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vicuna commented Jan 22, 2014

Comment author: @alainfrisch

Introduced by commit 14166, and more precisely this change:

            let op =
              match opt_exp with
                None -> None
              | Some exp -> get_path exp.exp_type
            in
            newvar (), op

---->

            begin match opt_exp with
              None -> newvar (), None
            | Some exp ->
                match get_path exp.exp_type with
                  None -> newvar (), None
                | Some (_, p', _) as op ->
                    let decl = Env.find_type p' env in
                    begin_def ();
                    let ty =
                      newconstr p' (instance_list env decl.type_params) in
                    end_def ();
                    generalize ty;
                    ty, op
            end

Removing the call to [generalize] seems to solve the issue. Jacques: is it a correct fix?

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vicuna commented Jan 23, 2014

Comment author: @garrigue

Fixed in revision 14415.
In this case we should only generalize the structure: use generalize_structure rather than generalize.

@vicuna vicuna closed this Dec 11, 2015

@vicuna vicuna added the typing label Mar 14, 2019

@vicuna vicuna added the bug label Mar 20, 2019

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