Format units longer than 255 bytes in full

NEWS.md

@@ -18,6 +18,9 @@
   repetition of a symbol, and reports each unrecognized symbol once; #441
   addressing #440 @billdenney
 
+* Format units longer than 255 bytes in full instead of silently truncating
+  them, which made e.g. `convert_to_base()` fail on such units; @billdenney
+
 # version 1.0-1
 
 * Add internal workaround for udunits2 bug with parsing of units that contain

src/udunits.cpp

@@ -284,7 +284,13 @@ CharacterVector R_ut_format(xut_unit p, bool names = false,
   if (definition)
     opt = opt | UT_DEFINITION;
   char buf[256];
-  if (ut_format(p, buf, sizeof(buf), opt) == sizeof(buf))
-    warning("buffer too small!"); // #nocov
-  return CharacterVector::create(buf);
+  int len = ut_format(p, buf, sizeof(buf), opt);
+  if (len < 0)
+    stop("cannot format unit"); // #nocov (r_error_fn throws first)
+  if (len < (int) sizeof(buf))
+    return CharacterVector::create(buf);
+  // ut_format() truncated the unit to fit, and returned the length it needs
+  std::vector<char> longer(len + 1);
+  ut_format(p, longer.data(), longer.size(), opt);
+  return CharacterVector::create(longer.data());
 }

tests/testthat/test_udunits.R

@@ -30,3 +30,23 @@ test_that("ud_convert works with vectors", {
 test_that("ud_convert returns Error for incompatible units", {
   expect_error(ud_convert(100, "m", "kg"), "Units not convertible")
 })
+
+test_that("units longer than 255 bytes are formatted in full", {
+  # 50 base units whose product formats as "zqaa.zqab.<...>", len bytes in all
+  long_unit <- function(len) {
+    syms <- paste0("zq", apply(expand.grid(letters, letters)[1:50, 2:1], 1,
+                               paste, collapse = ""))
+    syms[50] <- paste0(syms[50], strrep("z", len - 249))
+    syms
+  }
+  for (len in c(255, 256, 257, 300)) {
+    syms <- long_unit(len)
+    for (s in syms) install_unit(s)
+    u <- paste(syms, collapse = " ")
+    expect_identical(units:::ud_parse(u, definition = TRUE, ascii = TRUE),
+                     paste(syms, collapse = "."))
+    x <- set_units(1, u, mode = "standard")
+    expect_identical(units(convert_to_base(x))$numerator, syms)
+    remove_unit(syms)
+  }
+})