Simplify Ryaml_yoink() and preserve class attributes so handlers work with column.major = FALSE

[Copilot]

Ryaml_yoink() extracts single elements from data frame columns for row-major output but strips class attributes, so Date/POSIXt/factor handlers never match.

df <- data.frame(date = as.Date(c("2012-10-10", "2014-03-28")))
handler <- list(Date = function(x) as.character(x))

as.yaml(df, handlers = handler)                          # ✓ dates formatted
as.yaml(df, handlers = handler, column.major = FALSE)    # ✗ emits 15623.0, 16157.0

Changes

• src/r_emit.c: Simplify Ryaml_yoink() by removing the factor-specific code path that converted factors from INTSXP to STRSXP inline. Instead, always extract the raw value and call copyMostAttrib(s_vec, s_tmp) unconditionally, preserving class, tzone, levels, and other attributes on extracted elements. For factors, the existing emit_factor() in emit_object() handles level resolution correctly on the preserved single-element factor.
• tests/testthat/test-as_yaml.R: Add tests for Date, POSIXct, and factor columns with column.major = FALSE, including tests with custom handlers.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Unexpected interaction between column.major and Date handlers in as.yaml()</issue_title>
<issue_description>In as.yaml(), setting column.major=FALSE appears to prevent the application of Date handlers. For a while, I thought I was specifying my handler functions incorrectly, but I don't believe that is the case. I used these references for the handlers:

• Is there a way to control how Date objects are translated? #18
• https://github.com/r-lib/ymlthis/blob/15e54ad42ab7c1c10b96490c74e63999149afac1/R/yml.R#L184-L191

I've included a minimal example showing the difference in date handling when column.major=TRUE (default) vs. when column.major=FALSE. This interaction doesn't appear when using the verbatim_logical handler, making the Date behaviour entirely unexpected.

library(yaml)
library(purrr)

## Working date handling
date_handler <- list(Date = function(x) as.character(x))
my_list <- list(date = as.Date(c("2012-10-10", "2014-03-28")))
yaml::as.yaml(my_list, handlers = date_handler)
#> [1] "date:\n- '2012-10-10'\n- '2014-03-28'\n"
## instead of a list, use tibble and df (with column.major = TRUE by default)
my_tbl <- tibble::tibble(date = as.Date(c("2012-10-10", "2014-03-28")))
yaml::as.yaml(my_tbl, handlers = date_handler) |> cat()
#> date:
#> - '2012-10-10'
#> - '2014-03-28'
## but the date_handler doesn't apply with column.major = FALSE?
yaml::as.yaml(my_tbl, handlers = date_handler, column.major = FALSE) |> cat()
#> - date: 15623.0
#> - date: 16157.0

## Same issue with data.frames
my_df <- as.data.frame(my_tbl)
yaml::as.yaml(my_df, handlers = date_handler)
#> [1] "date:\n- '2012-10-10'\n- '2014-03-28'\n"
yaml::as.yaml(my_df, handlers = date_handler, column.major = FALSE)
#> [1] "- date: 15623.0\n- date: 16157.0\n"

## What if convert the tibble to list first?
# purrr::transpose also does the weird number conversion
purrr::transpose(my_tbl)
#> [[1]]
#> [[1]]$date
#> [1] 15623
#> 
#> 
#> [[2]]
#> [[2]]$date
#> [1] 16157
# but not if you do as.list() first
as.list(my_tbl) |>
    purrr::list_transpose(simplify = FALSE)
#> [[1]]
#> [[1]]$date
#> [1] "2012-10-10"
#> 
#> 
#> [[2]]
#> [[2]]$date
#> [1] "2014-03-28"

# what about logical handlers?
my_tbl$bool <- c(TRUE, FALSE)
verbatim_logical <- function(x) {
    result <- tolower(as.logical(x))
    class(result) <- "verbatim"
    return(result)
}
yml_handlers <- c(date_handler, list(logical = verbatim_logical))
# Logical handlers work fine either way, but dates depend on column.major
my_tbl |> yaml::as.yaml(handlers = yml_handlers, column.major = FALSE)
#> [1] "- date: 15623.0\n  bool: true\n- date: 16157.0\n  bool: false\n"
my_tbl |> yaml::as.yaml(handlers = yml_handlers, column.major = TRUE)
#> [1] "date:\n- '2012-10-10'\n- '2014-03-28'\nbool:\n- true\n- false\n"

^{Created on 2024-03-18 with reprex v2.0.2}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#>  setting  value
#>  version  R version 4.3.1 (2023-06-16)
#>  os       macOS Ventura 13.4.1
#>  system   aarch64, darwin20
#>  ui       X11
#>  language (EN)
#>  collate  en_US.UTF-8
#>  ctype    en_US.UTF-8
#>  tz       Australia/Melbourne
#>  date     2024-03-18
#>  pandoc   3.1.7 @ /opt/homebrew/bin/ (via rmarkdown)
#> 
#> ─ Packages ───────────────────────────────────────────────────────────────────
#>  package     * version date (UTC) lib source
#>  cli           3.6.1   2023-03-23 [1] CRAN (R 4.3.0)
#>  digest        0.6.33  2023-07-07 [1] CRAN (R 4.3.0)
#>  evaluate      0.21    2023-05-05 [1] CRAN (R 4.3.0)
#>  fansi         1.0.4   2023-01-22 [1] CRAN (R 4.3.0)
#>  fastmap       1.1.1   2023-02-24 [1] CRAN (R 4.3.0)
#>  fs            1.6.3   2023-07-20 [1] CRAN (R 4.3.0)
#>  glue          1.6.2   2022-02-24 [1] CRAN (R 4.3.0)
#>  htmltools     0.5.6   2023-08-10 [1] CRAN (R 4.3.0)
#>  knitr         1.43    2023-05-25 [1] CRAN (R 4.3.0)
#>  lifecycle     1.0.3   2022-10-07 [1] CRAN (R 4.3.0)
#>  magrittr      2.0.3   2022-03-30 [1] CRAN (R 4.3.0)
#>  pillar        1.9.0   2023-03-22 [1] CRAN (R 4.3.0)
#>  pkgconfig     2.0.3   2019-09-22 [1] CRAN (R 4.3.0)
#>  purrr       * 1.0.2   2023-08-10 [1] CRAN (R 4.3.0)
#>  R.cache       0.16.0  2022-07-21 [1] CRAN (R 4.3.0)
#>  R.methodsS3   1.8.2   2022-06-13 [1] CRAN (R 4.3.0)
#>  R.oo          1.25.0  2022-06-12 [1] CRAN (R 4.3.0)
#>  R.utils       2.12.2  2022-11-11 [1] CRAN (R 4.3.0)
#>  reprex        2.0.2   2022-08-17 [1] CRAN (R 4.3.0)
#>  rlang         1.1.1   2023-04-28 [1] CRAN (R 4.3.0)
#>  rmarkdown     2.24    2023-08-14 [1] CRAN (R 4.3.0)
#>  sessioninfo   1.2.2   2021-12-06 [1] CRAN (R 4.3.0)
#>  styler        1.10.1  2023-06-05 [1] CRAN (R 4.3.0)...

</details>



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- Fixes r-lib/yaml#141

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[krlmlr]

@copilot Why are factors treated specially? Add tests.

[Copilot]

@copilot Why are factors treated specially? Add tests.

Good point — there's no reason to special-case factors. Removed the factor-specific code path entirely in 6175d25. Ryaml_yoink() now always extracts the raw value and calls copyMostAttrib() unconditionally. For factors, this preserves the "factor" class and "levels" attribute on the yoinked INTSXP element, so emit_object()'s existing emit_factor() handles resolution correctly. Added tests for factor columns with and without handlers using column.major = FALSE.