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GeezerVison is showing github.com — Expand template argument type deduction by pfultz2 · Pull Request #8688 · cppcheck-opensource/cppcheck

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@pfultz2

@pfultz2 pfultz2 commented Jul 2, 2026

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Previously we only did type deduction when the argument that was passed was a literal(ie f(0)). This expands this to handle variables and expressions.

There is no varid/SymbolDatabase/ValueType information at the TemplateSimplifier stage so it uses a token-based parsing to try and deduce the type. If it can deduce the type then it will skip instantiating the function.

There is still a lot of gaps here that could be addressed in the future. Ideally, I would like to see if the logic from SymbolDatabase/ValueType could be reused here using a shared utility.

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Your Name added 17 commits July 2, 2026 09:43
Your Name
Add template type deduction
2c68b09
Your Name
Simplify
eecd903
Your Name
Use a forward walk
a43039a
Your Name
Handle global function template called from a class scope
695de6e
Your Name
Improve member functions
b60e55e
Your Name
Handle late class members
de77bc6
Your Name
Handle overloading better
90c62dc
Your Name
Simplify and add unit tests
5ad01ad
Your Name
Improve comments
965281d
Your Name
Avoid output params
d966681
Your Name
Format
f64190d
Your Name
Use stl algorithm
81da87b
Your Name
Format
9b554ac
Your Name
Fix selfcheck
35e830a
Your Name
Remvoe unnecessary move
770eeb9
Your Name
Add test for 13630
0e81fca
Your Name
Format
e87f8d7
@pfultz2

pfultz2 commented Jul 3, 2026

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This fixes issue 13630, so I added a test for that.
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firewave
firewave reviewed Jul 3, 2026
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Comment thread .selfcheck_suppressions
autoNoType:tools/triage/mainwindow.cpp
# ticket 11631
templateInstantiation:test/testutils.cpp
templateInstantiation

@firewave firewave Jul 3, 2026

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I would prefer to have an entry for each file it occurs in so we would at least partially detect future regressions. Heck, we should probably move this to the source instead so we have actual individual suppressions.

Since the scope has widened additional tickets probably need to be filed.

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@pfultz2 pfultz2 Jul 3, 2026

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Well we need to suppress it everytime we use functions like contains or calculate, and we are a long ways from being able to instantiate those functions. This isnt catching any errors and just adding burden. I think it would be better as a seperate report like daca.

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@firewave firewave Jul 3, 2026

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I see. It is just a debug warning (those are tracked in daca). Still a new ticket for one of the additional cases would be good for tracking.

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Your Name added 5 commits July 4, 2026 14:09
Your Name
Suppress unmatchedSuppression
9933641
Your Name
Merge
6dab97d
Your Name
Suppress unmatched suppression warnings with template instantiation
a6ded13
Your Name
Fix cppcheck debug warning
7f3645f
Your Name
Check for debug warnings flag
1f813e4
danmar
danmar reviewed Jul 9, 2026
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@danmar danmar left a comment •
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I agree it would be great to reuse the logic in symboldatabase etc..
It was a while since I looked at these things and I do not have a clear picture how complex it would be to achieve that. Reusing some functions sounds like a great idea.

There is a circular dependency; type deduction requires symboldatabase and symboldatabase requires type deduction so I fear that in theory we should rewrite the parser so that the templates are not instantiated as a separate step but rather do it all together at the same time.. instantiate templates, perform symboldatabase, create AST all at the same time. That is far too complex rewrite to do so I don't actually recommend that we do it in practice, it's more like "the ideal solution in theory". :-(

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Comment thread lib/templatesimplifier.cpp
Comment on lines +899 to 901
default:
return 0;
}

@danmar danmar Jul 9, 2026

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this default prevents such gcc warnings 1.cpp:6:12: warning: enumeration value ‘C’ not handled in switch [-Wswitch]

I would suggest that the default is removed. And below the switch call cppcheck::unreachable();

Suggested change
default:
return 0;
}
}
cppcheck::unreachable();

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Comment thread lib/templatesimplifier.cpp
if (a.isUnsigned || a.isUnsigned == b.isUnsigned)
return a;
// the lower ranked operand is unsigned, the higher ranked operand is signed
const std::size_t sizeA = arithSize(settings, a.arith);

@danmar danmar Jul 9, 2026

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I claim that the size does not matter. When 'long' and 'long long' have the same size:
'unsigned long' + 'signed long long' => 'signed long long'

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@pfultz2

pfultz2 commented Jul 9, 2026 •
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I agree it would be great to reuse the logic in symboldatabase etc.. It was a while since I looked at these things and I do not have a clear picture how complex it would be to achieve that. Reusing some functions sounds like a great idea.

There is a circular dependency; type deduction requires symboldatabase and symboldatabase requires type deduction so I fear that in theory we should rewrite the parser so that the templates are not instantiated as a separate step but rather do it all together at the same time.. instantiate templates, perform symboldatabase, create AST all at the same time. That is far too complex rewrite to do so I don't actually recommend that we do it in practice, it's more like "the ideal solution in theory". :-(

If we could make the symboldatabase/ast run incrementally then we can run this in a loop, so the TemplateSimplifier can use this information and then we run the symboldatabase/ast.

This is something I was working on as well, but I was looking into destroying the info everytime which makes it kind of expensive. If we could make it incremental, it might be doable.
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@danmar

danmar commented Jul 12, 2026

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This is something I was working on as well, but I was looking into destroying the info everytime which makes it kind of expensive. If we could make it incremental, it might be doable.

ok
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@pfultz2

pfultz2 commented Jul 13, 2026

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This is something I was working on as well, but I was looking into destroying the info everytime which makes it kind of expensive. If we could make it incremental, it might be doable.

ok

So in #8720, I did get it with a partially incremental update(it still rebuilds from scratches for class instantiations and template aliases). Some local tests showed it was about 2x faster with incremental updates vs rebuild everytime. I dont know if that is the direction we would prefer to go instead.
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@pfultz2 pfultz2 mentioned this pull request Jul 19, 2026
Fix 13630, 9676: Template argument deduction using SymbolDatabase #8720
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@pfultz2

pfultz2 commented Jul 27, 2026

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#8720 is a much better approach for this, so I am closing this.
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@pfultz2 pfultz2 closed this Jul 27, 2026
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@pfultz2 @danmar @firewave
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