Warn when not renaming

NEWS.md

@@ -1,5 +1,12 @@
 # rsi (development version)
 
+* `stack_rasters()` will only rename bands if `band_names` is the same length as 
+  the number of bands in the output raster (or missing, or defined by a 
+  function). It will now warn you if these lengths are different. Previously, if 
+  you provided more than the required number of band names, `stack_rasters()` 
+  would silently ignore the extra names, and would error if you provided fewer 
+  names than bands. 
+
 # rsi 0.1.2
 
 * `get_stac_data()` no longer includes `mask_band` in its outputs when 

R/stack_rasters.R

@@ -180,6 +180,8 @@ stack_rasters <- function(rasters,
   if (!missing(band_names) && is.function(band_names)) {
     var_names <- band_names(var_names)
   }
+  # technically we could have skipped reading the names of each raster here
+  # and just accepted the band names, but we want to check the CRS anyway
   if (!missing(band_names) && is.character(band_names)) {
     var_names <- band_names
   }
@@ -233,12 +235,26 @@ stack_rasters <- function(rasters,
 
   band_no <- 1
   vrt_bands <- vector("list", length(intermediate_vrt))
+
+  set_names <- FALSE
+  if (length(intermediate_vrt) == length(var_names)) {
+    set_names <- TRUE
+  } else if (!missing(band_names)) {
+    rlang::warn(
+      c(
+        "The number of band names provided did not match the number of bands in the output file.",
+        i = "Ignoring the provided band names and using default values instead."
+      ),
+      class = "rsi_band_name_length_mismatch"
+    )
+  }
+
   for (vrt in intermediate_vrt) {
     vrt <- readLines(vrt)
     band_def <- grep("VRTRasterBand", vrt)
     vrt <- vrt[seq(band_def[[1]], band_def[[2]])]
     vrt[1] <- gsub("band=\"1\"", paste0("band=\"", band_no, "\""), vrt[1])
-    if (length(intermediate_vrt) == length(var_names)) {
+    if (set_names) {
       vrt <- c(
         vrt[1],
         paste0("    <Description>", var_names[[band_no]], "</Description>"),

tests/testthat/test-stack_rasters.R

@@ -143,3 +143,23 @@ test_that("type_and_length checks", {
     error = TRUE
   )
 })
+
+test_that("stack_rasters warns when band names aren't the right length", {
+  expect_warning(
+    stack_rasters(
+      list(system.file("rasters/example_sentinel1.tif", package = "rsi")),
+      tempfile(fileext = ".vrt"),
+      band_names = "VH"
+    ),
+    class = "rsi_band_name_length_mismatch"
+  )
+
+  expect_warning(
+    stack_rasters(
+      list(system.file("rasters/example_sentinel1.tif", package = "rsi")),
+      tempfile(fileext = ".vrt"),
+      band_names = c("VH", "VV", "EXTRA")
+    ),
+    class = "rsi_band_name_length_mismatch"
+  )
+})