PR #505: accept .xlsx that lack a "styles" part (#528)

* Accept XLSX files that do not contain a "styles" part; fixes #506

An XLSX file that does not contain a "styles" part triggers this error:

  > read_excel("foo.xlsx", sheet="Sheet1")
  Error in sheets_fun(path) :
    Evaluation error: Couldn't find '' in 'foo.xlsx'.

To fix this, check for the presence of the part in cacheDateFormats() in
the same way that cacheStringTable() does.

* Rename test sheet; code style

* Beef up the test a bit

* Add NEWS bullet

NEWS.md

@@ -14,6 +14,8 @@
 
 ## Other changes
 
+* xlsx files that do not have a "Styles" part can now be read (#505, #506 @jt6)
+
 * Path handling:
 
   - All paths are passed through `normalizePath()` (#498, #499, new behaviour for xlsx but not xls) and `enc2native()` (#370).

src/XlsxWorkBook.h

@@ -267,6 +267,10 @@ class XlsxWorkBook {
   }
 
   void cacheDateFormats() {
+    if (!zip_has_file(path_, rel_.part("styles"))) {
+      return;
+    }
+
     std::string stylesXml = zip_buffer(path_, rel_.part("styles"));
     rapidxml::xml_document<> styles;
     styles.parse<rapidxml::parse_strip_xml_namespaces>(&stylesXml[0]);

tests/testthat/test-read-excel.R

@@ -115,3 +115,11 @@ test_that("non-ASCII filenames can be read", {
   expect_error_free(read_xls(tricky_xls_file))
   expect_error_free(read_xlsx(tricky_xlsx_file))
 })
+
+test_that("styles and sharedStrings parts can be absent", {
+  expect_error_free(
+    df <- read_xlsx(test_sheet("no-styles-or-sharedStrings-parts.xlsx"))
+  )
+  expect_identical(df$Language[1], "german")
+  expect_true(all(df$Age > 0))
+ })