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give more information in StringIndexError #36054

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Jun 5, 2020
Merged

give more information in StringIndexError #36054

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fc82c30
give more information in StringIndexError
KristofferC May 28, 2020
e409646
update for review
KristofferC Jun 3, 2020
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2 changes: 1 addition & 1 deletion base/strings/basic.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -133,7 +133,7 @@ julia> isvalid(str, 2)
false

julia> str[2]
ERROR: StringIndexError("αβγdef", 2)
ERROR: StringIndexError: invalid index [2], valid previous index [1] ('α'), valid next index [3] ('β')
Stacktrace:
[...]
```
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9 changes: 9 additions & 0 deletions base/strings/string.jl
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Expand Up @@ -11,6 +11,15 @@ struct StringIndexError <: Exception
end
@noinline string_index_err(s::AbstractString, i::Integer) =
throw(StringIndexError(s, Int(i)))
function Base.showerror(io::IO, exc::StringIndexError)
s = exc.string
i = thisind(s, exc.index)
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StringIndexError is exported and may be (mis)used by user code — maybe defensively check for exc.index < firstindex(s) && return invoke(showerror, Tuple{IO, Any}, io, exc) before doing something that may throw?

print(io, "StringIndexError: ", "invalid index [$(exc.index)], valid previous index [$i] ('$(s[i])')")
inext = nextind(s, i)
if !(inext > ncodeunits(s))
print(io, ", valid next index [$(inext)] ('$(s[inext])')")
end
end

const ByteArray = Union{Vector{UInt8},Vector{Int8}}

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9 changes: 5 additions & 4 deletions doc/src/manual/strings.md
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Expand Up @@ -281,11 +281,12 @@ julia> s[1]
'∀': Unicode U+2200 (category Sm: Symbol, math)

julia> s[2]
ERROR: StringIndexError("∀ x ∃ y", 2)
ERROR: StringIndexError: invalid index [2], valid previous index [1] ('∀'), valid next index [4] (' ')
Stacktrace:
[...]

julia> s[3]
ERROR: StringIndexError("∀ x ∃ y", 3)
ERROR: StringIndexError: invalid index [3], valid previous index [1] ('∀'), valid next index [4] (' ')
Stacktrace:
[...]

Expand All @@ -305,7 +306,7 @@ julia> s[end-1]
' ': ASCII/Unicode U+0020 (category Zs: Separator, space)

julia> s[end-2]
ERROR: StringIndexError("∀ x ∃ y", 9)
ERROR: StringIndexError: invalid index [9], valid previous index [7] ('∃'), valid next index [10] (' ')
Stacktrace:
[...]

Expand All @@ -325,7 +326,7 @@ julia> s[1:1]
"∀"

julia> s[1:2]
ERROR: StringIndexError("∀ x ∃ y", 2)
ERROR: StringIndexError: invalid index [2], valid previous index [1] ('∀'), valid next index [4] (' ')
Stacktrace:
[...]

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9 changes: 9 additions & 0 deletions test/strings/basic.jl
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Expand Up @@ -1074,3 +1074,12 @@ let x = SubString("ab", 1, 1)
@test y === x
chop("ab") === chop.(["ab"])[1]
end

@testset "show StringIndexError" begin
str = "abcdefghκijklmno"
e = StringIndexError(str, 10)
@test sprint(showerror, e) == "StringIndexError: invalid index [10], valid previous index [9] ('κ'), valid next index [11] ('i')"
str = "κ"
e = StringIndexError(str, 2)
@test sprint(showerror, e) == "StringIndexError: invalid index [2], valid previous index [1] ('κ')"
end