[llvm-bugs] [Bug 31237] New: lit substitutions don't work well when a substitution is a prefix of another

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31237

            Bug ID: 31237
           Summary: lit substitutions don't work well when a substitution
                    is a prefix of another
           Product: Test Suite
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: lit
          Assignee: unassignedbugs at nondot.org
          Reporter: dan at su-root.co.uk
                CC: daniel at zuster.org, llvm-bugs at lists.llvm.org,
                    modocache at gmail.com
    Classification: Unclassified

I was surprised to find today that lit was doing a substitution for me that I
wasn't expecting. It just so happened to be the "right thing" but this
behaviour could really bite us one day.

Concrete example:

Let's say we have

```
config.substitutions.append(('%klee', '/bin/klee'))
```

in our lit configuration file and we have a test that just contains

```
RUN: not echo %klee-stats
```

The test will fail with something like

```
******************** TEST 'KLEE :: regression/x.c' FAILED ********************
Script:
--
not /bin/klee-stats
--
Exit Code: 1
```

We can see that lit expanded the '%klee' in '%klee-stats'. Okay so I guess this
isn't too surprising but what if the lit configuration was this.

```
config.substitutions.append(('%klee', '/bin/klee'))
config.substitutions.append(('%klee-stats', '/bin/klee'))
```

then lit actually does the same thing it expands the RUN line to

```
not echo /bin/klee-stats
```

lit preferred the `%klee` substitution rather than the `%klee-stats` because it
is early in its list of substitutions than `%klee-stats`.

This might not be the behaviour that the user of lit expected.

I'm not sure the best way to handle this but I would suggest emitting a warning
if one of the user supplied substitutions is a prefix of another and the prefix
appears before the longer string in the list of substitutions to apply.

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