internal/libhive: anchor --sim regex matching at end of simulator name

[danceratopz]

Summary

The --sim flag uses unanchored regex matching (MatchString), so a pattern like engine matches all of:

• ethereum/engine
• eth2/engine
• ethereum/eels/consume-engine

because it appears as a substring of all three names.

This makes it impossible to select a specific simulator when another simulator's name is a superstring.

This concretely affects the addition of consume-enginex (#1403); adding this new simulator means that running ./hive --sim consume-engine changes existing behavior; 2 simulators now get run instead of 1.

Another example candidate in the future would be a new sync2 simulator; it would be impossible to run sync2 without also running sync.

This one-line fix appends $ to the user-supplied regex so patterns must match to the end of the simulator name.

Before

# Runs BOTH consume-engine and consume-enginex
./hive --sim ethereum/eels/consume-engine

After

# Runs only consume-engine
./hive --sim ethereum/eels/consume-engine

# Wildcards still work as expected
./hive --sim 'ethereum/eels/consume-.*'

Note

This is a minor behavior change: bare prefix patterns (e.g., --sim consume-) that previously matched via substring will no longer match unless a wildcard is added (--sim 'consume-.*'). Patterns that ended with a full simulator name (the common case) are unaffected.

[fjl]

I get the idea, but the user can also manually append $ to the regular expression. We have the matching like it is because that's how go test also works.

That said, I am not against making the matching more strict.

[danceratopz]

but the user can also manually append $ to the regular expression.

To have this as default was motivated by the fact that if we merge #1403 (consume-enginex), users will have to suddenly start appending $ (because a new simulator got added). I.e., an existing hive command ./hive --sim consume-engine changes behavior because a new simulator was added. Also, I really like the name enginex and I'd prefer not to change it :)

[fjl]

it could also be called xengine

[fjl]

I'm just kidding