From 8f1c1d5a27ee7fdd1a3934c567d6a57959ec9684 Mon Sep 17 00:00:00 2001
From: Ben Letham <bletham@gmail.com>
Date: Wed, 3 Mar 2021 14:35:36 -0800
Subject: [PATCH] Fix bug in timezone handling in R (#1501)

---
 R/DESCRIPTION                   |  1 +
 R/R/prophet.R                   | 25 ++++++++++++++++---------
 R/tests/testthat/test_prophet.R |  6 +++---
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/R/DESCRIPTION b/R/DESCRIPTION
index 777c135..6f9f0f7 100644
--- a/R/DESCRIPTION
+++ b/R/DESCRIPTION
@@ -24,6 +24,7 @@ Imports:
     extraDistr,
     ggplot2,
     grid,
+    lubridate,
     methods,
     RcppParallel (>= 5.0.1),
     rstan (>= 2.18.1),
diff --git a/R/R/prophet.R b/R/R/prophet.R
index f8e249e..19436a3 100644
--- a/R/R/prophet.R
+++ b/R/R/prophet.R
@@ -240,15 +240,15 @@ validate_column_name <- function(
 
 #' Convert date vector
 #'
-#' Convert the date to POSIXct object
+#' Convert the date to POSIXct object. Dates without a specified timezone will
+#' be given system time zone. Dates with specified timezone will keep it.
 #'
-#' @param ds Date vector, can be consisted of characters
-#' @param tz string time zone
+#' @param ds Date vector
 #'
 #' @return vector of POSIXct object converted from date
 #'
 #' @keywords internal
-set_date <- function(ds = NULL, tz = "GMT") {
+set_date <- function(ds) {
   if (length(ds) == 0) {
     return(NULL)
   }
@@ -257,12 +257,20 @@ set_date <- function(ds = NULL, tz = "GMT") {
     ds <- as.character(ds)
   }
 
-  if (min(nchar(ds), na.rm=TRUE) < 12) {
-    ds <- as.POSIXct(ds, format = "%Y-%m-%d", tz = tz)
+  # Type should be either character, or an object compatible with lubridate
+  if (is.character(ds)) {
+    if (min(nchar(ds), na.rm=TRUE) < 12) {
+        ds <- as.POSIXct(ds, format = "%Y-%m-%d")
+    } else {
+        ds <- as.POSIXct(ds, format = "%Y-%m-%d %H:%M:%S")
+    }
   } else {
-    ds <- as.POSIXct(ds, format = "%Y-%m-%d %H:%M:%S", tz = tz)
+    if (is.null(attr(ds, "tzone"))) {
+      # Make sure we don't default to GMT timezone
+      ds <- lubridate::force_tz(ds)
+    }
+    ds <- as.POSIXct(ds)
   }
-  attr(ds, "tzone") <- tz
   return(ds)
 }
 
@@ -1667,7 +1675,6 @@ make_future_dataframe <- function(m, periods, freq = 'day',
   dates <- dates[2:(periods + 1)]  # Drop the first, which is max(history$ds)
   if (include_history) {
     dates <- c(m$history.dates, dates)
-    attr(dates, "tzone") <- "GMT"
   }
   return(data.frame(ds = dates))
 }
diff --git a/R/tests/testthat/test_prophet.R b/R/tests/testthat/test_prophet.R
index 88469dc..b154da3 100644
--- a/R/tests/testthat/test_prophet.R
+++ b/R/tests/testthat/test_prophet.R
@@ -213,12 +213,12 @@ test_that("fourier_series_weekly", {
   true.values <- c(0.7818315, 0.6234898, 0.9749279, -0.2225209, 0.4338837,
                    -0.9009689)
   mat <- prophet:::fourier_series(DATA$ds, 7, 3)
-    expect_equal(true.values, mat[1, ], tolerance = 1e-6)
+    expect_equal(true.values, mat[177, ], tolerance = 1e-6)
 })
 
 test_that("fourier_series_yearly", {
-  true.values <- c(0.7006152, -0.7135393, -0.9998330, 0.01827656, 0.7262249,
-                   0.6874572)
+  true.values <- c(0.70112651, -0.71303690, -0.99985814, 0.01684324, 0.72474500,
+                   0.68901719)
   mat <- prophet:::fourier_series(DATA$ds, 365.25, 3)
     expect_equal(true.values, mat[1, ], tolerance = 1e-6)
 })