Fix bug in LayoutEngine.calculate(...)

The problem had been that `LayoutEngine.calculate(...)` was assuming
that len(char["text"]) would always equal 1, which is not true for
ligatures.

Thanks to @samkit-jain for finding a PDF that raised the error, and to
@bpugnaire for raising issue #683.

CHANGELOG.md

@@ -2,6 +2,12 @@
 
 All notable changes to this project will be documented in this file. The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
+## [0.7.2] - [unreleased]
+
+### Fixed
+
+- Fix bug in `LayoutEngine.calculate(...)` when processing char objects with len>1 representations, such as ligatures. ([#683](https://github.com/jsvine/pdfplumber/issues/683))
+
 ## [0.7.1] - 2022-05-31
 
 ### Fixed

pdfplumber/utils.py

@@ -450,7 +450,8 @@ class LayoutEngine:
                 num_spaces_prepend = max(min(1, line_len), round(x_dist) - line_len)
                 rendered += [(" ", None)] * num_spaces_prepend
                 for c in chars:
-                    rendered.append((c["text"], c))
+                    for letter in c["text"]:
+                        rendered.append((letter, c))
                 line_len += num_spaces_prepend + len(word["text"])
         return rendered
 

tests/test_issues.py

@@ -198,3 +198,19 @@ class Test(unittest.TestCase):
         with pdfplumber.open(path) as pdf:
             annots = pdf.annots
             annots[0]["contents"] == "日本語"
+
+    def test_issue_683(self):
+        """
+        Page.search ValueError: min() arg is an empty sequence
+
+        This ultimately stemmed from a mistaken assumption in
+        LayoutEngine.calculate(...) that len(char["text"]) would always equal
+        1, which is not true for ligatures. Issue 683 does not provide a PDF,
+        but the test PDF triggers the same error, which should now be fixed.
+
+        Thank you to @samkit-jain for identifying and writing this test.
+        """
+        path = os.path.join(HERE, "pdfs/issue-71-duplicate-chars-2.pdf")
+        with pdfplumber.open(path) as pdf:
+            page = pdf.pages[0]
+            page.search(r"\d+", regex=True)