Tuple bindings allow overwriting values

[silky]

Describe and demonstrate the bug

Seems like the tuple syntax allows overriding of variable names, that is otherwise disallowed by the compiler.

a = 1
a = 2 -- Error
(a) = 2 -- Fine

Example code

f = do
  (a, b) = (20, 50)
  (a, b) = (50, 90)
  x = 50
  -- x = 90 -- Uncomment and it gives an error
  (x) = 90
  printLine ("Prints 90: " ++ Nat.toText x)

Environment (please complete the following information):

• ucm --version: unison version: release/1.0.0 (built on 2025-11-21)
• OS/Architecture: linux

[runarorama]

(foo) = bar
baz

is syntactic shorthand for

match bar with 
  foo -> baz

So this is the behaviour I'd expect. Though I agree that it is confusing

[pchiusano]

Potentially we could add a warning, but I definitely don't want to warn for all variable shadowing. Especially in pattern matching, it is useful to deliberately shadow variables in the outer scope. So it's more of a judgement call whether we think that the variable shadowing here (or in other circumstances) is unintentional.

[silky]

My preference would be for overwriting variables to just not be disallowed at all; especially given that it seems to do the "Expected Thing" anyway; or is that perhaps not always the case?