[Bug][move-compiler-v2] V2 error messaging should show the assignments that lead to the type constraints

[brmataptos]

🐛 Bug

Two test cases illustrate this bug:

Case 1

This test case:

• third_party/move/move-compiler/tests/move_check/typing/assign_unpack_references_invalid.exp
• third_party/move/move-compiler-v2/tests/checking/typing/assign_unpack_references_invalid.exp

V2 shows an error like:

error: cannot assign `integer` to left-hand side of type `&u64`
  ┌─ tests/checking/typing/assign_unpack_references_invalid.move:9:9
  │
9 │         f = 0;
  │         ^

where the code is:

      2     struct S { f: u64 }
      ...
      6         let f;
      8         R { s1: S { f }, s2 } = &R { s1: S{f: 0}, s2: S{f: 1} };
      9         f = 0;

So the fact that the "left-hand side" f has type &u64 is indirect.

V1 has a better error message, which provides some context that explains the type of f:

error[E04007]: incompatible types
  ┌─ tests/move_check/typing/assign_unpack_references_invalid.move:9:9
  │
8 │         R { s1: S { f }, s2 } = &R { s1: S{f: 0}, s2: S{f: 1} };
  │                     - Expected: '&u64'
9 │         f = 0;
  │         ^
  │         │
  │         Invalid assignment to local 'f'
  │         Given: integer

.

Case 2

In this test case:

• third_party/move/move-compiler/tests/move_check/typing/assign_wrong_arity.exp
• third_party/move/move-compiler-v2/tests/checking/typing/assign_wrong_arity.exp
  V2 says something like:

error: tuple type `(integer, integer, integer)` is not allowed as a local variable type
  ┌─ tests/checking/typing/assign_wrong_arity.move:5:13
  │
5 │         let x;
  │             ^
  │
  = required by declaration of local `x`

where the relevant code is:

      5         let x;
      6         x = ();
      7         x = (0, 1, 2);

so it points to the declaration of x but doesn't show the assignment which tries to assign a tuple-typed value to it.

[github-actions]

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