From 08ff36fa0ca365000197341b9540ff7126711497 Mon Sep 17 00:00:00 2001
From: Uchida Mizuki <uchidamizuki@vivaldi.net>
Date: Sun, 6 Aug 2023 05:42:27 +0900
Subject: [PATCH] Fix bug in `str_trunc()`  (#515)

Fixes #512
---
 NEWS.md                     |  3 +++
 R/trunc.R                   |  7 ++++---
 tests/testthat/test-trunc.R | 41 ++++++++++++++++++++++++++++++++-----
 3 files changed, 43 insertions(+), 8 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index 5c539c63..28b85b61 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,8 @@
 # stringr (development version)
 
+* `str_trunc()` now correctly truncates strings when `side` is `"left"` or 
+  `"center"` (@UchidaMizuki, #512).
+
 # stringr 1.5.0
 
 ## Breaking changes
diff --git a/R/trunc.R b/R/trunc.R
index b48c78bf..4a0a7106 100644
--- a/R/trunc.R
+++ b/R/trunc.R
@@ -23,7 +23,8 @@ str_trunc <- function(string, width, side = c("right", "left", "center"),
   side <- arg_match(side)
   check_string(ellipsis)
 
-  too_long <- !is.na(string) & str_length(string) > width
+  len <- str_length(string)
+  too_long <- !is.na(string) & len > width
   width... <- width - str_length(ellipsis)
 
   if (width... < 0) {
@@ -34,11 +35,11 @@ str_trunc <- function(string, width, side = c("right", "left", "center"),
 
   string[too_long] <- switch(side,
     right  = str_c(str_sub(string[too_long], 1, width...), ellipsis),
-    left   = str_c(ellipsis, str_sub(string[too_long], -width..., -1)),
+    left   = str_c(ellipsis, str_sub(string[too_long], len[too_long] - width... + 1, -1)),
     center = str_c(
         str_sub(string[too_long], 1, ceiling(width... / 2)),
         ellipsis,
-        str_sub(string[too_long], -floor(width... / 2), -1)
+        str_sub(string[too_long], len[too_long] - floor(width... / 2) + 1, -1)
       )
   )
   string
diff --git a/tests/testthat/test-trunc.R b/tests/testthat/test-trunc.R
index 1bb80614..58c0a58d 100644
--- a/tests/testthat/test-trunc.R
+++ b/tests/testthat/test-trunc.R
@@ -18,15 +18,27 @@ test_that("truncations work for all elements of a vector", {
 
 test_that("truncations work for all sides", {
 
-  trunc <- function(direction) str_trunc(
+  trunc <- function(direction, width) str_trunc(
     "This string is moderately long",
     direction,
-    width = 20
+    width = width
   )
 
-  expect_equal(trunc("right"),   "This string is mo...")
-  expect_equal(trunc("left"),    "...s moderately long")
-  expect_equal(trunc("center"),  "This stri...ely long")
+  expect_equal(trunc("right", 20),  "This string is mo...")
+  expect_equal(trunc("left", 20),   "...s moderately long")
+  expect_equal(trunc("center", 20), "This stri...ely long")
+
+  expect_equal(trunc("right", 3),  "...")
+  expect_equal(trunc("left", 3),   "...")
+  expect_equal(trunc("center", 3), "...")
+
+  expect_equal(trunc("right", 4),  "T...")
+  expect_equal(trunc("left", 4),   "...g")
+  expect_equal(trunc("center", 4), "T...")
+
+  expect_equal(trunc("right", 5),  "Th...")
+  expect_equal(trunc("left", 5),   "...ng")
+  expect_equal(trunc("center", 5), "T...g")
 })
 
 test_that("does not truncate to a length shorter than elipsis", {
@@ -35,3 +47,22 @@ test_that("does not truncate to a length shorter than elipsis", {
     str_trunc("foobar", 3, ellipsis = "....")
   })
 })
+
+test_that("str_trunc correctly snips rhs-of-ellipsis for truncated strings", {
+  trunc <- function(width, side) {
+    str_trunc(c("", "a", "aa", "aaa", "aaaa", "aaaaaaa"), width, side,
+              ellipsis = "..")
+  }
+
+  expect_equal(trunc(4, "right"), c("", "a", "aa", "aaa", "aaaa", "aa.."))
+  expect_equal(trunc(4, "left"), c("", "a", "aa", "aaa", "aaaa", "..aa"))
+  expect_equal(trunc(4, "center"), c("", "a", "aa", "aaa", "aaaa", "a..a"))
+
+  expect_equal(trunc(3, "right"), c("", "a", "aa", "aaa", "a..", "a.."))
+  expect_equal(trunc(3, "left"), c("", "a", "aa", "aaa", "..a", "..a"))
+  expect_equal(trunc(3, "center"), c("", "a", "aa", "aaa", "a..", "a.."))
+
+  expect_equal(trunc(2, "right"), c("", "a", "aa", "..", "..", ".."))
+  expect_equal(trunc(2, "left"), c("", "a", "aa", "..", "..", ".."))
+  expect_equal(trunc(2, "center"), c("", "a", "aa", "..", "..", ".."))
+})