setnames() on duplicate columns produces unexpected key

``` r library(data.table) dt <- data.table(a = 1:3, b = 4:6, b = 7:9, check.names = FALSE) setkey(dt, a, b, b) unique_names <- make.unique(names(dt)) setnames(dt, unique_names) key(dt) == unique_names #> [1] TRUE FALSE FALSE dt2 <- data.table(a = 1:3, b = 4:6, b = 7:9, check.names = FALSE) setkey(dt2, a, b, b) nms <- c('blah', 'foo', 'zap') setnames(dt2, nms) key(dt2) == nms #> [1] TRUE FALSE FALSE ``` ^{Created on 2026-05-08 with [reprex v2.1.1](https://reprex.tidyverse.org)} <details style="margin-bottom:10px;"> <summary> Session info </summary> ``` r sessioninfo::session_info() #> ─ Session info ─────────────────────────────────────────────────────────────── #> setting value #> version R version 4.5.3 (2026-03-11) #> os Ubuntu 22.04.5 LTS #> system x86_64, linux-gnu #> ui X11 #> language en_AU:en #> collate en_AU.UTF-8 #> ctype en_AU.UTF-8 #> tz Australia/Melbourne #> date 2026-05-08 #> pandoc 3.8.3 @ /usr/lib/rstudio/resources/app/bin/quarto/bin/tools/x86_64/ (via rmarkdown) #> quarto 1.7.31 @ /usr/local/bin/quarto #> #> ─ Packages ─────────────────────────────────────────────────────────────────── #> package * version date (UTC) lib source #> cli 3.6.5 2025-04-23 [1] CRAN (R 4.5.2) #> data.table * 1.18.4 2026-05-06 [1] CRAN (R 4.5.3) #> digest 0.6.39 2025-11-19 [1] CRAN (R 4.5.2) #> evaluate 1.0.5 2025-08-27 [1] CRAN (R 4.5.1) #> fastmap 1.2.0 2024-05-15 [1] CRAN (R 4.5.0) #> fs 1.6.6 2025-04-12 [1] CRAN (R 4.5.0) #> glue 1.8.0 2024-09-30 [1] CRAN (R 4.5.0) #> htmltools 0.5.9 2025-12-04 [1] CRAN (R 4.5.2) #> knitr 1.50 2025-03-16 [1] CRAN (R 4.5.0) #> lifecycle 1.0.4 2023-11-07 [1] CRAN (R 4.5.1) #> reprex 2.1.1 2024-07-06 [1] CRAN (R 4.5.3) #> rlang 1.1.7 2026-01-09 [1] CRAN (R 4.5.2) #> rmarkdown 2.30 2025-09-28 [1] CRAN (R 4.5.2) #> rstudioapi 0.17.1 2024-10-22 [1] CRAN (R 4.5.0) #> sessioninfo 1.2.3 2025-02-05 [1] CRAN (R 4.5.0) #> withr 3.0.2 2024-10-28 [1] CRAN (R 4.5.0) #> xfun 0.54 2025-10-30 [1] CRAN (R 4.5.2) #> yaml 2.3.12 2025-12-10 [1] CRAN (R 4.5.2) #> #> [1] /home/mpc/R/x86_64-pc-linux-gnu-library/4.5 #> [2] /usr/local/lib/R/site-library #> [3] /usr/lib/R/site-library #> [4] /usr/lib/R/library #> * ── Packages attached to the search path. #> #> ────────────────────────────────────────────────────────────────────────────── ``` </details>