Uninformative error message in calc mode when confusing types

[Mr-vedant-gupta]

Prerequisites

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• Reduce the issue to a minimal, self-contained, reproducible test case.
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Description

When using calc mode, on accidentally using 1/2 : ℕ (which rounds to 0) instead of 1/2 : ℝ due to a forgotten type cast, I get a confusing type mismatch error message where the expected and current types are identical.

Context

https://leanprover.zulipchat.com/#narrow/channel/113489-new-members/topic/Calc.20mode.20complaining.20about.20non-matching.20expressions

Steps to Reproduce

import Mathlib

theorem nonsense (a b  : ℝ) :
  ((a + b) ^ 2 ) ^ (1/2 : ℝ)  = 1 :=
by
  calc
    ((a + b) ^ 2) ^ (1 / 2) = 1 := by sorry -- forgot to cast (1 / 2) to ℝ

Expected behavior: [Clear and concise description of what you expect to happen]
An error message like

invalid 'calc' step, left-hand side is
  ((a + b) ^ 2) ^ (1 / 2) : ℕ 
but is expected to be
  ((a + b) ^ 2) ^ (1 / 2) : ℝ

Actual behavior: [Clear and concise description of what actually happens]
Lean throws this error message

invalid 'calc' step, left-hand side is
  ((a + b) ^ 2) ^ (1 / 2) : ℝ
but is expected to be
  ((a + b) ^ 2) ^ (1 / 2) : ℝ