Fix completion on empty command (#4418)

Author: IanButterworth

ext/REPLExt/REPLExt.jl

@@ -39,8 +39,13 @@ function LineEdit.complete_line(c::PkgCompletionProvider, s; hint::Bool = false)
     # Convert to new completion interface format
     named_completions = map(LineEdit.NamedCompletion, ret)
     # Convert UnitRange to Region (Pair{Int,Int}) to match new completion interface
-    # range represents character positions in full string, convert to 0-based byte positions
-    if isempty(range)
+    # range represents character positions in partial string, convert to 0-based byte positions
+    if length(range) == 0 && first(range) > last(range)
+        # Empty backward range like 4:3 means insert at cursor position
+        # The cursor is at position last(range), so insert after it
+        pos = thisind(partial, last(range) + 1) - 1
+        region = pos => pos
+    elseif isempty(range)
         region = 0 => 0
     else
         # Convert 1-based character positions to 0-based byte positions

test/repl.jl

@@ -403,6 +403,12 @@ temp_pkg_dir() do project_path
             @test "Example" in c
             pkg"free Example"
 
+            # Test for issue #59829 - completion with only trailing space should work
+            # When typing "rm <TAB>" with Example installed, should complete to "rm Example"
+            c, r = test_complete("rm ")
+            @test "Example" in c
+            @test apply_completion("rm ") == "rm Example"
+
             # Test deduplication of already-specified packages (issue #4098)
             # After typing "rm Example ", typing "E" should not suggest Example again
             c, r = test_complete("rm Example E")