plots: fix resolve template path bug

Fix: iterative#6854

dvc/repo/plots/template.py

@@ -109,16 +109,16 @@ def templates_dir(self):
     @staticmethod
     def _find(templates, template_name):
         for template in templates:
-            if (
-                template_name == template
-                or template_name + ".json" == template
+            if template.endswith(template_name) or template.endswith(
+                template_name + ".json"
             ):
                 return template
         return None
 
     def _find_in_project(self, name: str) -> Optional["StrPath"]:
-        if os.path.exists(name):
-            return name
+        full_path = os.path.abspath(name)
+        if os.path.exists(full_path):
+            return full_path
 
         if os.path.exists(self.templates_dir):
             templates = [

tests/unit/render/test_vega.py

@@ -451,3 +451,29 @@ def test_find_vega(tmp_dir, dvc):
         first(plot_content["layer"])["encoding"]["x"]["field"] == INDEX_FIELD
     )
     assert first(plot_content["layer"])["encoding"]["y"]["field"] == "y"
+
+
+@pytest.mark.parametrize(
+    "template_path, target_name",
+    [
+        (os.path.join(".dvc", "plots", "template.json"), "template"),
+        (os.path.join(".dvc", "plots", "template.json"), "template.json"),
+        (
+            os.path.join(".dvc", "plots", "subdir", "template.json"),
+            os.path.join("subdir", "template.json"),
+        ),
+        (
+            os.path.join(".dvc", "plots", "subdir", "template.json"),
+            os.path.join("subdir", "template"),
+        ),
+        ("template.json", "template.json"),
+    ],
+)
+def test_should_resolve_template(tmp_dir, dvc, template_path, target_name):
+    os.makedirs(os.path.abspath(os.path.dirname(template_path)), exist_ok=True)
+    with open(template_path, "w", encoding="utf-8") as fd:
+        fd.write("template_content")
+
+    assert dvc.plots.templates._find_in_project(
+        target_name
+    ) == os.path.abspath(template_path)