Narrow locals after definite reassignment and in-condition assignment

[apiology]

Problem: Solargraph reports a call as unresolved on a local it has already been given enough to narrow.

# @param tasks [Array<String>, nil]
def guarded_default(tasks)
  tasks = ['a'] if tasks.nil?
  tasks.each { |t| puts t }   # Unresolved call to each on Array<String>, nil
end

Five shapes are affected, each reduced from a suppression carried in a consuming codebase.

1. Parameter reassigned to a non-literal — the declared @param type won over the reassignment.

position = normalize(position)   # @return [Position]
position.line                    # flagged against Array(Integer, Integer)

2. Nil-guarded default used past the conditional — the non-firing path kept the original type.

tasks = ['a'] if tasks.nil?
tasks.each { |t| t }             # Unresolved call to each on Array<String>, nil

3. Narrowing outliving a definite reassignment — the guard's downcast survived onto the new value.

return if str.nil?; str = fetch_name
str.length                       # Unresolved call to length on nil, Boolean

4. Dominating reassignment not counted as definite — definite stayed false on both sides.

if flag then x = normalize(x); x.line end
# x.line kept the declared @param type, not Position

5. Variable assigned inside an if condition — narrowing ran before the condition was mapped.

if (md = name.match(/x/)) then md[0] end
# md[0]: Unresolved call to [] on MatchData, nil

Solution: Pin::BaseVariable records whether an assignment definitely executed and which compound statement it was made in, so a superseding reassignment replaces the earlier type instead of unioning with it; condition processing covers parenthesised and assignment expressions, and runs after the condition is mapped.

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