[IslamElsayed]

Motivation

Closes #2504

The Ruby LSP can extract a variable but can't inline one.

Implementation

• CodeActions offers "Refactor: Inline Variable" (refactor.inline) when the cursor or selection is on a local variable's name, at its assignment or at a read. As with the other refactors, the resolve request does the work.

• The resolver finds the scope that declares the variable, using Prism's depth to step out of blocks. It collects every assignment and read of the variable there, skipping block parameters that shadow it. It then replaces each read with the assigned value and removes the assignment: the whole line, or a = 1; when it shares a line.

• Parentheses follow your suggestion, but are based on operator precedence rather than added every time. The example in the issue stays b = 5 * 10 - 5, while a = 5 - 10; b = a * 5 becomes b = (5 - 10) * 5. It also handles ** grouping to the right, negative literals, receivers ((1..3).to_a), and/or, and hashes passed without parentheses. When unsure, it adds them.

• It refuses, with a message, when inlining could change behaviour:

  • The variable is assigned more than once (including += and multiple assignment) or is a parameter.
  • The assignment is part of an expression (foo(a = 1)), or might not run before a read (a = 1 if cond; puts a).
  • A variable the value reads is reassigned before the value is read. When a read is inside a block, any later reassignment counts.
  • The value calls methods or builds objects (strings, arrays, hashes), unless it's read exactly once, unconditionally, in the next statement. This way a call never runs more or fewer times, or later, than before.
  • The value contains a heredoc.

  The fourth rule is stricter than what I described in the issue: moving a call past other statements can change its result too.

The part most worth a careful look is needs_parentheses? and its precedence table.

Automated Tests

• Fixtures with expectations: the example from the issue, the parentheses case, inlining from a read, and an assignment followed by ;. One more expectation checks that the action is offered.
• test/requests/inline_variable_test.rb covers the precedence cases and each refusal.
• The full suite, Sorbet and RuboCop pass locally on Ruby 4.0.7. The one exception is the backtrace test in server_test.rb, which expects the checkout directory to be named ruby-lsp.

Manual Tests

1. Open a Ruby file with:

   def foo
     a = 5 - 10
     puts a
     b = a * 5
   end

2. Put the cursor on a in a = 5 - 10, or on either read, and open the code actions menu.
3. Choose "Refactor: Inline Variable". The body becomes puts 5 - 10 and b = (5 - 10) * 5.
4. Change 5 - 10 to compute and try again. The action is offered but refuses with a message, because compute would run twice.

I use AI assistance when working on patches, and I check and test everything before submitting.

[IslamElsayed]

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