From 259505a1660a696c397b6981903b199513efbd98 Mon Sep 17 00:00:00 2001
From: Gauarv Chaudhary <chaudharygaurav2004@gmail.com>
Date: Sun, 21 Dec 2025 21:24:28 +0530
Subject: [PATCH 1/2] test: add failing tests for facet error messages

Issue #168 - facet_wrap(. ~ var) gives unhelpful error when var is missing.

Added tests that will pass once we improve error messages in animint2dir().
Tests cover facet_wrap and facet_grid with missing variables.

These tests are animint2-specific .
---
 .../test-renderer-facet-error-messages.R      | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 tests/testthat/test-renderer-facet-error-messages.R

diff --git a/tests/testthat/test-renderer-facet-error-messages.R b/tests/testthat/test-renderer-facet-error-messages.R
new file mode 100644
index 00000000..4add970e
--- /dev/null
+++ b/tests/testthat/test-renderer-facet-error-messages.R
@@ -0,0 +1,32 @@
+acontext("Facet error messages")
+test_that("facet_wrap formula with missing variable gives clear error", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_wrap(. ~ NonExistentColumn) +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  expect_error(
+    animint2dir(viz, out.dir = tempfile(), open.browser = FALSE),
+    "NonExistentColumn"
+  )
+})
+test_that("facet_grid formula with missing variable gives clear error", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_grid(. ~ MissingVar) +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  expect_error(
+    animint2dir(viz, out.dir = tempfile(), open.browser = FALSE),
+    "MissingVar"
+  )
+})
+test_that("facet_wrap string notation works", {
+  viz <- list(
+    scatter = ggplot() +
+      facet_wrap("Species") +
+      geom_point(aes(Sepal.Length, Petal.Length), data = iris)
+  )
+  info <- animint2dir(viz, out.dir = tempfile(), open.browser = FALSE)
+  expect_true(file.exists(file.path(info$out.dir, "index.html")))
+})

From 24721558434248fdbdd2e8f112d1cdcd648e7254 Mon Sep 17 00:00:00 2001
From: Gauarv Chaudhary <chaudharygaurav2004@gmail.com>
Date: Mon, 22 Dec 2025 09:30:27 +0530
Subject: [PATCH 2/2] fix: improve error message for missing facet variables

When facet_wrap or facet_grid uses formula notation with a variable
that does not exist in the data, the error now shows:
- Which variable is missing
- What columns are available
- Suggests using string notation instead

Fixes #168
---
 R/z_animint.R        |  3 +++
 R/z_animintHelpers.R | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/R/z_animint.R b/R/z_animint.R
index 3beb7dd7..0f6c371e 100644
--- a/R/z_animint.R
+++ b/R/z_animint.R
@@ -21,6 +21,9 @@ parsePlot <- function(meta, plot, plot.name){
     }
   }
 
+  ## Validate facet variables before ggplot_build (Issue #168)
+  checkFacetVariables(plot)
+
   built <- ggplot_build(plot)
   plot.info <- list()
 
diff --git a/R/z_animintHelpers.R b/R/z_animintHelpers.R
index f3686454..a0844e24 100644
--- a/R/z_animintHelpers.R
+++ b/R/z_animintHelpers.R
@@ -1066,3 +1066,40 @@ selectSSandCS <- function(aesthetics_list){
   ## TODO: how to handle showSelected$ignored in prev animint code??
   return(aes.list)
 }
+
+checkFacetVariables <- function(plot){
+  facet <- plot$facet
+  if(is.null(facet)) return(invisible())
+  facet_class <- class(facet)[1]
+  facet_vars <- character(0)
+  if(facet_class == "wrap" && length(facet$facets) > 0){
+    facet_vars <- names(facet$facets)
+    facet_vars <- facet_vars[facet_vars != "."]
+  }else if(facet_class == "grid"){
+    row_vars <- names(facet$rows)
+    col_vars <- names(facet$cols)
+    facet_vars <- c(row_vars, col_vars)
+    facet_vars <- facet_vars[facet_vars != "."]
+  }
+  if(length(facet_vars) == 0) return(invisible())
+  all_data_vars <- character(0)
+  for(layer in plot$layers){
+    if(length(layer$data) > 0){
+      all_data_vars <- c(all_data_vars, names(layer$data))
+    }
+  }
+  if(length(plot$data) > 0){
+    all_data_vars <- c(all_data_vars, names(plot$data))
+  }
+  all_data_vars <- unique(all_data_vars)
+  missing_vars <- setdiff(facet_vars, all_data_vars)
+  if(length(missing_vars) > 0){
+    stop(sprintf(
+      "Facet variable%s not found in data: %s\nAvailable columns: %s\nUse string notation like facet_wrap(\"var\") instead of formula notation facet_wrap(. ~ var)",
+      if(length(missing_vars) > 1) "s" else "",
+      paste(missing_vars, collapse = ", "),
+      paste(all_data_vars, collapse = ", ")
+    ))
+  }
+  invisible()
+}