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[modules] Remove headers deprecated in C++17 and non-standard in C++20 from the module maps #20794

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guitargeek merged 3 commits into from
Jan 13, 2026
Merged

[modules] Remove headers deprecated in C++17 and non-standard in C++20 from the module maps #20794

guitargeek merged 3 commits into from
Jan 13, 2026
+112 −139

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@guitargeek guitargeek commented Jan 4, 2026

Remove the headers ccomplex, cstdalign, cstdbool, and ctgmath from the module maps. They are deprecated since C++17 and should not be included anymore by ROOT or its users, as C++17 is the minimum supported C++ standard.

This fixes build warnings that can be seen in the CI when building with GCC 15, for example on Fedora 42:

[ 47%] Generating G__Core.cxx, ../lib/Core.pcm
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:5:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/ccomplex:51:4: warning: "<ccomplex> is deprecated in C++17, use <complex> instead" [-W#warnings]
 # warning "<ccomplex> is deprecated in C++17, use <complex> instead"
   ^
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:23:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cstdalign:50:6: warning: "<cstdalign> is deprecated in C++17, remove the #include" [-W#warnings]
 #   warning "<cstdalign> is deprecated in C++17, remove the #include"
     ^
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:25:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cstdbool:50:6: warning: "<cstdbool> is deprecated in C++17, remove the #include" [-W#warnings]
 #   warning "<cstdbool> is deprecated in C++17, remove the #include"
     ^
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:30:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/ctgmath:50:6: warning: "<ctgmath> is deprecated in C++17, use <complex> or <cmath> instead" [-W#warnings]
 #   warning "<ctgmath> is deprecated in C++17, use <complex> or <cmath> instead"

@guitargeek guitargeek self-assigned this Jan 4, 2026
@guitargeek guitargeek requested a review from bellenot as a code owner January 4, 2026 10:26
@guitargeek guitargeek requested a review from dpiparo as a code owner January 4, 2026 10:26
@guitargeek guitargeek added the clean build Ask CI to do non-incremental build on PR label Jan 4, 2026
@dpiparo dpiparo requested review from devajithvs and hahnjo January 4, 2026 10:34
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dpiparo commented Jan 4, 2026

I added @hahnjo and @devajithvs to the reviewers.

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guitargeek commented Jan 4, 2026

Thanks! Note that there is one more warning about a non-standard header in C++20, but I don't know what we can do about that since still have to support C++17:

While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:12:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/ciso646:49:6: warning: "<ciso646> is not a standard header since C++20, use <version> to detect implementation-specific macros" [-W#warnings]
#    warning "<ciso646> is not a standard header since C++20, use <version> to detect implementation-specific macros"

Can we also do something about that?

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github-actions bot commented Jan 4, 2026 •
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Test Results

    22 files      22 suites   3d 17h 45m 57s ⏱️
 3 791 tests  3 791 ✅ 0 💤 0 ❌
80 314 runs  80 314 ✅ 0 💤 0 ❌

Results for commit 37ee619.

♻️ This comment has been updated with latest results.

ferdymercury
ferdymercury reviewed Jan 5, 2026
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hahnjo commented Jan 9, 2026

Thanks! Note that there is one more warning about a non-standard header in C++20, but I don't know what we can do about that since still have to support C++17:

[...]

Can we also do something about that?

I guess you can try requires !cplusplus20, that should only build the module with C++17 because later standards always define all previous versions.

@hahnjo hahnjo requested a review from vgvassilev January 9, 2026 07:54
@guitargeek
[modules] Remove headers deprecated in C++17 from the module maps
d90db28 
Remove the headers `ccomplex`, `cstdalign`, `cstdbool`, and `ctgmath`
from the module maps. They are deprecated since C++17 and should not be
included anymore by ROOT or its users, as C++17 is the minimum supported
C++ standard.

This fixes build warnings that can be seen in the CI when building with
GCC 15, for example on Fedora 42:

```txt
[ 47%] Generating G__Core.cxx, ../lib/Core.pcm
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:5:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/ccomplex:51:4: warning: "<ccomplex> is deprecated in C++17, use <complex> instead" [-W#warnings]
 # warning "<ccomplex> is deprecated in C++17, use <complex> instead"
   ^
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:23:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cstdalign:50:6: warning: "<cstdalign> is deprecated in C++17, remove the #include" [-W#warnings]
 #   warning "<cstdalign> is deprecated in C++17, remove the #include"
     ^
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:25:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cstdbool:50:6: warning: "<cstdbool> is deprecated in C++17, remove the #include" [-W#warnings]
 #   warning "<cstdbool> is deprecated in C++17, remove the #include"
     ^
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:30:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/ctgmath:50:6: warning: "<ctgmath> is deprecated in C++17, use <complex> or <cmath> instead" [-W#warnings]
 #   warning "<ctgmath> is deprecated in C++17, use <complex> or <cmath> instead"
```
@guitargeek
Format code of getSTLIncludes() function in makepchinput.py
c69d67b 
This is done to make the ruff linter happy.
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guitargeek commented Jan 9, 2026

Thanks! Note that there is one more warning about a non-standard header in C++20, but I don't know what we can do about that since still have to support C++17:
[...]
Can we also do something about that?

I guess you can try requires !cplusplus20, that should only build the module with C++17 because later standards always define all previous versions.

Nice, that works!

@guitargeek
[modules] Remove ciso646 from the module maps - non standard in C++20
37ee619 
Remove the `ciso646` header from the module maps. It is not part of the
C++20 standard, and should not be included anymore by ROOT or its users
if they compile ROOT with C++20 or higher.

Note that also higher C++ versions will also define the `cplusplus20`
variable, as newer standards always define all previous versions.

This fixes build warnings that can be seen in the CI when building with
GCC 15, for example on Fedora 42:

```txt
While building module 'Core':
While building module 'std' imported from input_line_1:1:
In file included from <module-includes>:12:
/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/ciso646:49:6: warning: "<ciso646> is not a standard header since C++20, use <version> to detect implementation-specific macros" [-W#warnings]
 #   warning "<ciso646> is not a standard header since C++20, use <version> to detect implementation-specific macros"
```
@guitargeek guitargeek changed the title [modules] Remove headers deprecated in C++17 from the module maps [modules] Remove headers deprecated in C++17 and non-standard in C++20 from the module maps Jan 9, 2026
hahnjo
hahnjo approved these changes Jan 12, 2026
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Looks good to me.

@guitargeek guitargeek merged commit 6478dae into root-project:master Jan 13, 2026
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@guitargeek guitargeek deleted the deprecated_headers branch January 13, 2026 10:29
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@hahnjo hahnjo hahnjo approved these changes

@bellenot bellenot Awaiting requested review from bellenot bellenot is a code owner

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@devajithvs devajithvs Awaiting requested review from devajithvs

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@ferdymercury ferdymercury ferdymercury left review comments

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