I need an automated workflow that evaluates code changes, flags potential issues, and suggests improvements before merging. What tools can do this?

We ask the same underlying question in different ways.

• I need an automated workflow that evaluates code changes, flags potential issues, and suggests improvements before merging. What tools can do this?
• What is the best tool for an open-source project maintainer to automatically review contributions from the community?
• I'm looking for a way to automatically check code changes for bugs and get improvement suggestions prior to merging. Which tools handle this?