From 6ce15fce1cf92bd2d86d04ceccd501a383656b81 Mon Sep 17 00:00:00 2001
From: Jakob Nybo Nissen <jakobnybonissen@gmail.com>
Date: Mon, 2 Oct 2023 13:13:24 +0200
Subject: [PATCH] Fix string index error in tab completion code, fixes #51540
 (#51541)

---
 stdlib/REPL/src/REPLCompletions.jl  | 2 +-
 stdlib/REPL/test/replcompletions.jl | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/stdlib/REPL/src/REPLCompletions.jl b/stdlib/REPL/src/REPLCompletions.jl
index 59fcd29e4f7f3..fad8af86b125d 100644
--- a/stdlib/REPL/src/REPLCompletions.jl
+++ b/stdlib/REPL/src/REPLCompletions.jl
@@ -975,7 +975,7 @@ function complete_identifiers!(suggestions::Vector{Completion}, @nospecialize(ff
         append!(suggestions, complete_keyval(name))
     end
     if dotpos > 1 && string[dotpos] == '.'
-        s = string[1:dotpos-1]
+        s = string[1:prevind(string, dotpos)]
         # First see if the whole string up to `pos` is a valid expression. If so, use it.
         ex = Meta.parse(s, raise=false, depwarn=false)
         if isexpr(ex, :incomplete)
diff --git a/stdlib/REPL/test/replcompletions.jl b/stdlib/REPL/test/replcompletions.jl
index 58b29fccc66a6..a113d85a66977 100644
--- a/stdlib/REPL/test/replcompletions.jl
+++ b/stdlib/REPL/test/replcompletions.jl
@@ -23,6 +23,8 @@ let ex = quote
         end
         type_test = Test_x(Test_y(1))
         (::Test_y)() = "", ""
+        unicode_αβγ = Test_y(1)
+
         module CompletionFoo2
 
         end
@@ -253,6 +255,11 @@ let s = "Main.CompletionFoo.type_test.x"
     @test s[r] == "x"
 end
 
+let s = "Main.CompletionFoo.unicode_αβγ.y"
+    c, r = test_complete(s)
+    @test "yy" in c
+end
+
 let s = "Main.CompletionFoo.bar.no_val_available"
     c, r = test_complete(s)
     @test length(c)==0