FileSystemLoader include paths in error (#1663)

CHANGES.rst

@@ -35,6 +35,8 @@ Unreleased
 -   Fix `copy`/`pickle` support for the internal ``missing`` object.
     :issue:`2027`
 -   ``Environment.overlay(enable_async)`` is applied correctly. :pr:`2061`
+-   The error message from ``FileSystemLoader`` includes the paths that were
+    searched. :issue:`1661`
 
 
 Version 3.1.4

src/jinja2/loaders.py

@@ -204,7 +204,12 @@ def get_source(
             if os.path.isfile(filename):
                 break
         else:
-            raise TemplateNotFound(template)
+            plural = "path" if len(self.searchpath) == 1 else "paths"
+            paths_str = ", ".join(repr(p) for p in self.searchpath)
+            raise TemplateNotFound(
+                template,
+                f"{template!r} not found in search {plural}: {paths_str}",
+            )
 
         with open(filename, encoding=self.encoding) as f:
             contents = f.read()

tests/test_loader.py

@@ -179,6 +179,24 @@ def test_filename_normpath(self):
         t = e.get_template("foo/test.html")
         assert t.filename == str(self.searchpath / "foo" / "test.html")
 
+    def test_error_includes_paths(self, env, filesystem_loader):
+        env.loader = filesystem_loader
+
+        with pytest.raises(TemplateNotFound) as info:
+            env.get_template("missing")
+
+        e_str = str(info.value)
+        assert e_str.startswith("'missing' not found in search path: ")
+
+        filesystem_loader.searchpath.append("other")
+
+        with pytest.raises(TemplateNotFound) as info:
+            env.get_template("missing")
+
+        e_str = str(info.value)
+        assert e_str.startswith("'missing' not found in search paths: ")
+        assert ", 'other'" in e_str
+
 
 class TestModuleLoader:
     archive = None