BUG: Raise MergeError when suffixes result in duplicate column names (GH#61402)

Author: Farsidetfs

pandas/core/reshape/merge.py

@@ -3058,6 +3058,15 @@ def renamer(x, suffix: str | None):
     llabels = left._transform_index(lrenamer)
     rlabels = right._transform_index(rrenamer)
 
+    #FIXED: https://github.com/pandas-dev/pandas/issues/61402
+    # Check for duplicates after renaming
+    overlap_issues = llabels.intersection(rlabels)
+    if len(overlap_issues) > 0:
+        raise MergeError(
+            "Passing 'suffixes' which cause duplicate columns "
+            f"{set(overlap_issues)} is not allowed."
+        )
+    
     dups = []
     if not llabels.is_unique:
         # Only warn when duplicates are caused because of suffixes, already duplicated