CPP: Add query for CWE-1126: Declaration of Variable with Unnecessarily Wide Scope

[ihsinme]

Good day.
in this request I am looking at the error of using a new variable inside a loop.
in a situation where a variable with the same name participates in a loop condition.

the most dangerous situation is the while loop in the absence of changes to the variables participating in the condition.
At this stage, I tried to minimize false positives as much as possible.
I left the situation of changing a variable through a function call. as I considered it a rather rare practice. if you disagree with me, I will listen to you

current PR.
sleuthkit/sleuthkit#2329

[geoffw0]

This reminds me of the queries in Best Practices/Hiding, especially cpp/declaration-hides-variable. Your query appears to be a more specialized version looking for instances where there's evidence the hiding is causing a real problem.

[ihsinme]

thanks for your comments.
they are very helpful.

[geoffw0]

Started a test run on LGTM: https://lgtm.com/query/3978555328191505856/

[ihsinme]

Started a test run on LGTM: https://lgtm.com/query/3978555328191505856/

good day.
I looked at the launch results.
I would like to point out the following
1.In the project ArtifexSoftware/ghostpdl, the detection on the change of a variable did not work, I need some time to figure it out.
2. libretro/libretro-uae WohlSoft/PGE-Project php/php-src projects showed false detection as I hastily replaced this.getCondition().GetAChild*(). this eliminated the control of changes for all variables in the loop condition. I will probably return the old version.

[ihsinme]

thanks for the note with recursion.
with its help, I managed to get rid of a number of logical negatives in the class constructor.
I also added two new loops to the test file.

[geoffw0]

I've reported the comment two up, I think it might be some kind of spam. I suggest we ignore it and continue working on the query...

[geoffw0]

Changes look good to me, we seem to have lost some false positive results including https://lgtm.com/projects/g/php/php-src/snapshot/1d919127b62b1c3d0c7e50b7925896dfa7831d0f/files/ext/opcache/Optimizer/zend_optimizer.c?sort=name&dir=ASC&mode=heatmap#L623 and https://lgtm.com/projects/g/WohlSoft/PGE-Project/snapshot/4443036d0b7cf288c4d962b1faf61f053d07d279/files/Engine/common_features/QTranslatorX/qm_translator.cpp?sort=name&dir=ASC&mode=heatmap#L1040

[geoffw0]

I think you've addressed all of the suggestions, the QL is satisfactory and the tests are excellent.

Results on LGTM: https://lgtm.com/query/8106651676569760712/ (very few, probably because we're looking for cases that are definitely causing problems rather than just any instances of reusing variable names).