[PATCH v2] libcamera: base: Remove custom __nodiscard attribute

[Laurent Pinchart]

Hi Mattijs,

Thank you for the patch.

On Mon, Jan 06, 2025 at 10:40:41AM +0100, Mattijs Korpershoek wrote:
> __nodiscard was introduced for compatibility with C++14.
> In C++17, there is an official attribute: [[nodiscard]].
> Moreover, some libc implementations (like bionic) already define the
> __nodiscard macro [1].
> 
> Since:
> - libcamera builds with cpp_std=c++17
> - [[nodiscard]] is already used in the android HAL (exif)
> 
> We should replace all usage __nodiscard of by [[nodiscard]] for
> consistency.
> 
> Do the replacement and remove the no longer used compiler.h.
> 
> [1] https://android-review.googlesource.com/c/platform/bionic/+/3254860
> 
> Signed-off-by: Mattijs Korpershoek <mkorpershoek at baylibre.com>

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> ---
> Hi, it's been a while. I've found a (trivial) build issue when
> building against recent bionic versions.
> 
> After discussion in v1, dropping compiler.h seemed the right choice.
> ---
> Changes in v2:
> - Drop support of __nodiscard instead of adding another #ifdef (Laurent)
> - Link to v1: https://lists.libcamera.org/pipermail/libcamera-devel/2025-January/047922.html
> ---
>  include/libcamera/base/compiler.h  | 14 --------------
>  include/libcamera/base/meson.build |  1 -
>  include/libcamera/base/unique_fd.h |  3 +--
>  include/libcamera/geometry.h       | 28 +++++++++++++---------------
>  4 files changed, 14 insertions(+), 32 deletions(-)
> 
> diff --git a/include/libcamera/base/compiler.h b/include/libcamera/base/compiler.h
> deleted file mode 100644
> index fda8fdfdc543f86c5554e38ef790c00d72d60389..0000000000000000000000000000000000000000
> --- a/include/libcamera/base/compiler.h
> +++ /dev/null
> @@ -1,14 +0,0 @@
> -/* SPDX-License-Identifier: LGPL-2.1-or-later */
> -/*
> - * Copyright (C) 2021, Google Inc.
> - *
> - * Compiler support
> - */
> -
> -#pragma once
> -
> -#if __cplusplus >= 201703L
> -#define __nodiscard		[[nodiscard]]
> -#else
> -#define __nodiscard
> -#endif
> diff --git a/include/libcamera/base/meson.build b/include/libcamera/base/meson.build
> index 2a0cee317204b0d6b44276703fac229bfd7973b9..f28ae4d42a69c755710b51ffc92976bb6fb6a0d8 100644
> --- a/include/libcamera/base/meson.build
> +++ b/include/libcamera/base/meson.build
> @@ -5,7 +5,6 @@ libcamera_base_include_dir = libcamera_include_dir / 'base'
>  libcamera_base_public_headers = files([
>      'bound_method.h',
>      'class.h',
> -    'compiler.h',
>      'flags.h',
>      'object.h',
>      'shared_fd.h',
> diff --git a/include/libcamera/base/unique_fd.h b/include/libcamera/base/unique_fd.h
> index c9a3b5d0e8628533bd18649e156ba78da40ca200..3066bf28f745df1d26a74c20d21b607dba3d41f4 100644
> --- a/include/libcamera/base/unique_fd.h
> +++ b/include/libcamera/base/unique_fd.h
> @@ -10,7 +10,6 @@
>  #include <utility>
>  
>  #include <libcamera/base/class.h>
> -#include <libcamera/base/compiler.h>
>  
>  namespace libcamera {
>  
> @@ -43,7 +42,7 @@ public:
>  		return *this;
>  	}
>  
> -	__nodiscard int release()
> +	[[nodiscard]] int release()
>  	{
>  		int fd = fd_;
>  		fd_ = -1;
> diff --git a/include/libcamera/geometry.h b/include/libcamera/geometry.h
> index e5f0a843d3144d2086c42c11ab40b0a98438a7e2..0a7133f24c78d4b70075fdd02eabfa52857937dc 100644
> --- a/include/libcamera/geometry.h
> +++ b/include/libcamera/geometry.h
> @@ -11,8 +11,6 @@
>  #include <ostream>
>  #include <string>
>  
> -#include <libcamera/base/compiler.h>
> -
>  namespace libcamera {
>  
>  class Rectangle;
> @@ -110,7 +108,7 @@ public:
>  		return *this;
>  	}
>  
> -	__nodiscard constexpr Size alignedDownTo(unsigned int hAlignment,
> +	[[nodiscard]] constexpr Size alignedDownTo(unsigned int hAlignment,
>  						 unsigned int vAlignment) const
>  	{
>  		return {
> @@ -119,7 +117,7 @@ public:
>  		};
>  	}
>  
> -	__nodiscard constexpr Size alignedUpTo(unsigned int hAlignment,
> +	[[nodiscard]] constexpr Size alignedUpTo(unsigned int hAlignment,
>  					       unsigned int vAlignment) const
>  	{
>  		return {
> @@ -128,7 +126,7 @@ public:
>  		};
>  	}
>  
> -	__nodiscard constexpr Size boundedTo(const Size &bound) const
> +	[[nodiscard]] constexpr Size boundedTo(const Size &bound) const
>  	{
>  		return {
>  			std::min(width, bound.width),
> @@ -136,7 +134,7 @@ public:
>  		};
>  	}
>  
> -	__nodiscard constexpr Size expandedTo(const Size &expand) const
> +	[[nodiscard]] constexpr Size expandedTo(const Size &expand) const
>  	{
>  		return {
>  			std::max(width, expand.width),
> @@ -144,7 +142,7 @@ public:
>  		};
>  	}
>  
> -	__nodiscard constexpr Size grownBy(const Size &margins) const
> +	[[nodiscard]] constexpr Size grownBy(const Size &margins) const
>  	{
>  		return {
>  			width + margins.width,
> @@ -152,7 +150,7 @@ public:
>  		};
>  	}
>  
> -	__nodiscard constexpr Size shrunkBy(const Size &margins) const
> +	[[nodiscard]] constexpr Size shrunkBy(const Size &margins) const
>  	{
>  		return {
>  			width > margins.width ? width - margins.width : 0,
> @@ -160,10 +158,10 @@ public:
>  		};
>  	}
>  
> -	__nodiscard Size boundedToAspectRatio(const Size &ratio) const;
> -	__nodiscard Size expandedToAspectRatio(const Size &ratio) const;
> +	[[nodiscard]] Size boundedToAspectRatio(const Size &ratio) const;
> +	[[nodiscard]] Size expandedToAspectRatio(const Size &ratio) const;
>  
> -	__nodiscard Rectangle centeredTo(const Point &center) const;
> +	[[nodiscard]] Rectangle centeredTo(const Point &center) const;
>  
>  	Size operator*(float factor) const;
>  	Size operator/(float factor) const;
> @@ -294,11 +292,11 @@ public:
>  	Rectangle &scaleBy(const Size &numerator, const Size &denominator);
>  	Rectangle &translateBy(const Point &point);
>  
> -	__nodiscard Rectangle boundedTo(const Rectangle &bound) const;
> -	__nodiscard Rectangle enclosedIn(const Rectangle &boundary) const;
> -	__nodiscard Rectangle scaledBy(const Size &numerator,
> +	[[nodiscard]] Rectangle boundedTo(const Rectangle &bound) const;
> +	[[nodiscard]] Rectangle enclosedIn(const Rectangle &boundary) const;
> +	[[nodiscard]] Rectangle scaledBy(const Size &numerator,
>  				       const Size &denominator) const;
> -	__nodiscard Rectangle translatedBy(const Point &point) const;
> +	[[nodiscard]] Rectangle translatedBy(const Point &point) const;
>  
>  	Rectangle transformedBetween(const Rectangle &source,
>  				     const Rectangle &target) const;
> 
> ---
> base-commit: 35ed4b91291d9f3d08e4b51acfb51163e65df8f8
> change-id: 20250103-nodiscard-redef-9158e8fdc3f5

-- 
Regards,

Laurent Pinchart