Analysis: Follow state into the locals it is assigned to - #2289
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A template reads state and then names it something else. `<% total = @items.size %>` puts `@items` in `total`, and `<%= total %>` was attributed to nothing, so changing `@items` looked like it touched one node when it decides two. This is the same shape as a block parameter, which carries state under another name for as long as its block is open, and it is bound the same way. A local carries whatever its right hand side reads, which makes chains work without anything extra: `a = @items.size` then `b = a * 2` puts both `a` and `b` in reach of `@items`. Only the right hand side counts, so `@items == other` binds nothing, since a comparison assigns nothing. Scope is the block that made the assignment. A local first assigned inside a block is gone when the block closes, the way Ruby has it, so an alias set is snapshotted on entry and restored on exit instead of subtracting what was added. A partial's declared locals are its state, and `dependency_index` enumerated only instance variables and constants, so asking what a partial's `query` reaches returned nothing at all. They are enumerated now. All three languages, with the same five templates asserted in each. Rust and TypeScript reach the assignment through the prism node they already carry, and slice the right hand side by the offsets it gives them.
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This pull request teaches the dependency analysis that a local assigned from a piece of state carries that state.
totalis@items, counted. Matching is by name, so nothing connected the two andtotalwas attributed to nothing, which meantherb dependenciesandherb actionview flowleft the paragraph out of what@itemsreaches.Follow up on #2288, which did the same for the names a block binds. This is the other way a state gets a second name.
An assignment binds the name only when its right hand side reads the state, and the name carries it for as long as the assignment is in scope.
acarries@itemsandbcarriesa, sobreaches back to@itemsthrough the chain.Three cases that look like assignments and are not:
<% other = 5 %>binds nothing, because nothing on the right reads the state.<% if total == @items.size %>is a comparison, andtotalis left alone.