How does genhtml detect common filename prefix

[my-umd]

(Using lcov 2.1)
I noticed that the automatically detected common filename prefix is not accurate when there are two forward slashes (at the beginning of the pathname). E.g., SF://export/home/tomcat/TeamCity/Agent/src/internal/filename. When I ran genhtml, I see this from my console:
Found common filename prefix "/"
While the actual common filename pattern is //export/home/tomcat/TeamCity/Agent/src/internal.
I understand that the extra forward slash is not correct here. But seems genhtml will not correctly identify the common pattern when it is present. I did a test by removing the extra forward slash from my trace file, and verified that genhtml works correctly in this case. Not sure if this is a bug.

[henry2cox]

A feature - but not a bug.
lcov/genhtml/geninfo do not try to be clever with respect to files and paths. If string is identical, the file is the same. If string differs - then not.
I suspect that it found / as the common prefix because some paths in your input data started with // and some with / - and genhtml gave up on commoning when it saw the first difference.

For this specific issue, you can use genhtml --substitute 's#//#/#' ... to tell the tool to munge the path before processing (you may need the quotes so your shell doesn't think it saw a comment character).

[my-umd]

Ok, thanks @henry2cox.