index-from-length

Flag two suspect for-loop iteration specs. First, for i in 1:length(x) (or 1:size(x, d)) where the loop variable then indexes x: prefer eachindex(x) (or axes(x, d)), which stays correct for collections whose indices are not one-based. The match is name-based — any length/size call counts — and, lacking type information to exempt collections that really are one-based like Vector, the rule is opinionated, so it only fires when the loop variable actually indexes the collection. Second, for i in 3.5: iterating a bare numeric literal runs the loop body once and is almost always a mistaken range. No fix is offered, since the rewrites are not always equivalent.

1:length(x) used to index x:

for i in 1:length(x)
    println(x[i])
end

warning: index-from-length
 --> example.jl:1:10
  |
1 | for i in 1:length(x)
  |          ^^^^^^^^^^^ iterate `eachindex(x)` instead of `1:length(x)`

Iterating a bare number loops once:

for i in 3.5
    println(i)
end

warning: index-from-length
 --> example.jl:1:10
  |
1 | for i in 3.5
  |          ^^^ iterating a numeric literal runs the loop body once; did you mean a range?