Fix #1523

Author: wlandau

NEWS.md

@@ -6,6 +6,7 @@
 * Improve reporter deprecation messages (#1493, @dakvid).
 * Clarify scope of `tar_renv()` (#1506, @valentingar).
 * Handle errors in `rstudioapi::isAvailable()` (#1519, @dipterix).
+* Improve error message when metadata file is corrupted (#1523, @dakvid).
 
 # targets 1.11.3
 

R/class_database.R

@@ -528,23 +528,28 @@ database_class <- R6::R6Class(
         return()
       }
       line <- readLines(self$path, n = 1L)
-      header <- strsplit(line, split = database_sep_outer, fixed = TRUE)[[1]]
+      header <- if_any(
+        length(line) > 0L,
+        strsplit(line, split = database_sep_outer, fixed = TRUE)[[1]],
+        ""
+      )
       if (identical(header, self$header)) {
         return()
       }
       tar_throw_file(
-        "invalid header in ",
+        "invalid header in the {targets} database file ",
         self$path,
         "\n",
         "  found:    ",
         paste(header, collapse = database_sep_outer),
         "\n",
         "  expected: ",
         paste(self$header, collapse = database_sep_outer),
-        "\nProbably because of a breaking change in the targets package. ",
-        "Before running tar_make() again, ",
-        "either delete the data store with tar_destroy() ",
-        "or downgrade the targets package to an earlier version."
+        "\nEither there was a breaking change in the {targets} package ",
+        "or the metadata file was corrupted somehow. ",
+        "Before running tar_make() again, either delete the aforementioned ",
+        "database file, or if applicable, ",
+        "downgrade the {targets} package to an earlier version."
       )
     },
     validate = function() {

R/class_meta.R

@@ -182,6 +182,9 @@ meta_class <- R6::R6Class(
         return()
       }
       line <- readLines(self$database$path, n = 1)
+      if (!length(line)) {
+        return()
+      }
       line <- strsplit(line, split = database_sep_outer, fixed = TRUE)[[1]]
       if ("repository" %in% line) {
         return()

tests/testthat/test-class_meta.R

@@ -351,6 +351,18 @@ tar_test("migrate meta database", {
   expect_equal(tar_read(x), "value")
 })
 
+tar_test("migrate meta database", {
+  temp <- tempfile()
+  meta <- meta_init(path_store = temp)
+  on.exit({
+    meta$database$close()
+    unlink(temp, recursive = TRUE)
+  })
+  dir.create(dirname(meta$database$path), recursive = TRUE)
+  file.create(meta$database$path)
+  expect_no_error(meta$migrate_database())
+})
+
 tar_test("meta$preprocess() on empty data", {
   for (write in c(TRUE, FALSE)) {
     meta <- meta_init(path_store = tempfile())