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Fix a panic on a field write through a slice element - #42
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The nonmutating analyzer stopped the whole run with exit status 2 on a
field write whose container was not an identifier. `containerStorageVisible`
accepted only an identifier and panicked on every other expression, and
`visibleMutationOrigin` called it for the container of each selector
write. These shapes crashed:
//constable:nonmutating
func F(s []E) { s[0].N = 1 } // *ast.IndexExpr
//constable:nonmutating
func G(p *E) { (*p).N = 1 } // *ast.StarExpr
//constable:nonmutating
func H(ss [][]E) { ss[0][0].N = 1 } // nested *ast.IndexExpr
A selector's container lives in caller-visible memory exactly when the
container expression does, so `exprRefersToCallerVisibleMemory` subsumes
`containerStorageVisible` for an identifier and answers for the other
shapes without a panic. Delete the narrower function and call the general
one at both sites.
`rootOrigin` finds the parameter or receiver that starts a chain, so a
write below an index or a dereference reports the identifier that the
caller passed. The same change removes two silent misses that the old
container check produced: `o.inner.data[0] = 0` on a value receiver now
reports, and so does `(*p).inner.data[0] = 0` on a pointer parameter.
Add regression cases for the three crashing shapes and for the value
receiver chain, which passed silently before. Keep `o.inner = Inner{}` as
a control: a field write on the receiver copy must stay unreported.
Change-Id: Iade884a097fb704a54fc026e0c9d245f54989fdc
nnutter
changed the title
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