From 1715110da6a9f7a1f1774281e5bbb8d953c3ba60 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E7=90=86=E5=BF=B5=E5=9C=88?=
 <73381027+Rratic@users.noreply.github.com>
Date: Tue, 30 Aug 2022 21:29:03 +0800
Subject: [PATCH] Enhance `StringIndexError` display (correct escaping)
 (#46039)

---
 base/strings/string.jl | 6 ++++--
 test/strings/basic.jl  | 5 +++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/base/strings/string.jl b/base/strings/string.jl
index e44746f9834d9..3d8db74d7b795 100644
--- a/base/strings/string.jl
+++ b/base/strings/string.jl
@@ -17,10 +17,12 @@ function Base.showerror(io::IO, exc::StringIndexError)
     if firstindex(s) <= exc.index <= ncodeunits(s)
         iprev = thisind(s, exc.index)
         inext = nextind(s, iprev)
+        escprev = escape_string(s[iprev:iprev])
         if inext <= ncodeunits(s)
-            print(io, ", valid nearby indices [$iprev]=>'$(s[iprev])', [$inext]=>'$(s[inext])'")
+            escnext = escape_string(s[inext:inext])
+            print(io, ", valid nearby indices [$iprev]=>'$escprev', [$inext]=>'$escnext'")
         else
-            print(io, ", valid nearby index [$iprev]=>'$(s[iprev])'")
+            print(io, ", valid nearby index [$iprev]=>'$escprev'")
         end
     end
 end
diff --git a/test/strings/basic.jl b/test/strings/basic.jl
index c1f1473daa236..c9b6e425f6a9c 100644
--- a/test/strings/basic.jl
+++ b/test/strings/basic.jl
@@ -726,6 +726,11 @@ end
     @test_throws ArgumentError "abc"[BitArray([true, false, true])]
 end
 
+@testset "issue #46039 enhance StringIndexError display" begin
+    @test sprint(showerror, StringIndexError("αn", 2)) == "StringIndexError: invalid index [2], valid nearby indices [1]=>'α', [3]=>'n'"
+    @test sprint(showerror, StringIndexError("α\n", 2)) == "StringIndexError: invalid index [2], valid nearby indices [1]=>'α', [3]=>'\\n'"
+end
+
 @testset "concatenation" begin
     @test "ab" * "cd" == "abcd"
     @test 'a' * "bc" == "abc"