fix #581, report dangerous indexing

src/analyzers/jetanalyzer.jl

@@ -1148,6 +1148,14 @@ function report_serious_exception!(analyzer::JETAnalyzer, sv::InferenceState, ar
                     return true
                 end
             end
+        elseif widenconst(a) <: ArgumentError
+            # promote `ArgumentError` thrown by `to_index` method
+            # so that we get reports from dangerous indexing (aviatesk/JET.jl#581)
+            def = sv.linfo.def
+            if isa(def, Method) && def.name === :to_index
+                add_new_report!(analyzer, sv.result, SeriousExceptionReport(sv, ArgumentError("invalid index"), get_lin((sv, get_currpc(sv)))))
+                return true
+            end
         end
     end
     return false

test/analyzers/test_jetanalyzer.jl

@@ -428,6 +428,21 @@ end
     end
 end
 
+func_invalid_index(xs, i) = xs[i]
+func_invalid_index(xs::Vector{Int}) = xs[findfirst(>(0), xs)]
+@testset "report invalid index" begin
+    let result = report_call(func_invalid_index, (Vector{Int},Nothing))
+        @test count(get_reports_with_test(result)) do r
+            r isa SeriousExceptionReport
+        end == 1
+    end
+    let result = report_call(func_invalid_index, (Vector{Int},))
+        @test count(get_reports_with_test(result)) do r
+            r isa SeriousExceptionReport
+        end == 1
+    end
+end
+
 @testset "DivideError" begin
     let result = report_call() do
             div(1, 0)