Fix POSIXt precision and tzone

NEWS.md

@@ -1,5 +1,15 @@
 # bigrquery (development version)
 
+* Change rendering for uploading `POSIXt`-class objects to 6 digits
+  with `"%OS6"` (#660). This means that all timestamps will have
+  microsecond resolution when uploading data.
+
+* Set the `"tzone"` attribute of uploaded `POSIXt` columns to
+  `Sys.timezone()` when the timezone is empty or not defined (#660).
+  Previously, if unset then it may be interpreted as UTC regardless of
+  the system's local timezone, resulting in a round-trip value
+  differing by the TZ offset.
+
 # bigrquery 1.6.1
 
 * Fix test failure on CRAN.

R/bq-perform.R

@@ -187,7 +187,13 @@ export_json <- function(values) {
 
   # Convert times to canonical format
   is_time <- vapply(values, function(x) inherits(x, "POSIXt"), logical(1))
-  values[is_time] <- lapply(values[is_time], format, "%Y-%m-%d %H:%M:%S")
+  values[is_time] <- lapply(values[is_time], function(x) {
+    if (is.null(attr(x, "tzone")) || attr(x, "tzone") %in% c(NA, "")) {
+      attr(x, "tzone") <- Sys.timezone()
+    }
+    ifelse(is.na(x), NA_character_,
+           paste(format(x, "%Y-%m-%d %H:%M:%OS6"), attr(x, "tzone")))
+  })
 
   # Convert wk_wkt to text
   is_wk <- vapply(values, function(x) inherits(x, "wk_vctr"), logical(1))

tests/testthat/test-bq-digits-secs.R

@@ -0,0 +1,45 @@
+test_that("'POSIXt' preserves microsecond precision", {
+  tbl <- data.frame(psx = trunc.Date(Sys.time(), units = "secs") + 0.123456)
+  attr(tbl$psx, "tzone") <- "UTC"
+
+  ds <- bq_table(bq_test_project(), "basedata", "datatypes")
+  defer(try(bq_table_delete(ds), silent = TRUE))
+
+  bq_table_upload(ds, tbl)
+  tbl2 <- bq_table_download(ds)
+
+  expect_equal(tbl$psx, tbl2$psx)
+})
+
+test_that("'tzone' unset and different values handled correctly", {
+  # the bug only produced problems when the system TZ has a non-zero
+  # offset (i.e., not UTC)
+  withr::local_envvar(TZ = "America/New_York")
+
+  ds <- bq_table(bq_test_project(), "basedata", "datatypes")
+  defer(try(bq_table_delete(ds), silent = TRUE))
+
+  tbl1in <- tibble(psx = trunc.Date(Sys.time(), units = "secs") + 0.123456)
+  attr(tbl1in$psx, "tzone") <- NULL
+  bq_table_upload(ds, tbl1in)
+  tbl1out <- bq_table_download(ds)
+  bq_table_delete(ds)
+  attr(tbl1out$psx, "tzone") <- NULL
+  expect_equal(tbl1in$psx, tbl1out$psx)
+  expect_true(abs(as.numeric(tbl5$psx - tbl$psx, units = "hours")) < 1)
+
+  tbl2in <- tibble(psx = trunc.Date(Sys.time(), units = "secs") + 0.123456)
+  attr(tbl2in$psx, "tzone") <- "UTC"
+  bq_table_upload(ds, tbl2in)
+  tbl2out <- bq_table_download(ds)
+  bq_table_delete(ds)
+  expect_equal(tbl2in$psx, tbl2out$psx)
+
+  tbl3in <- tibble(psx = trunc.Date(Sys.time(), units = "secs") + 0.123456)
+  attr(tbl3in$psx, "tzone") <- "America/New_York"
+  bq_table_upload(ds, tbl3in)
+  tbl3out <- bq_table_download(ds)
+  bq_table_delete(ds)
+  attr(tbl3out$psx, "tzone") <- attr(tbl3in$psx, "tzone")
+  expect_equal(tbl3in$psx, tbl3out$psx)
+})