From 81fbdf1e460fd198a53903cc8f250cc4508f25fe Mon Sep 17 00:00:00 2001
From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Date: Tue, 22 Apr 2025 10:04:40 +0300
Subject: pixelformats: Disable constexpr for older compilers

gcc 11 and earlier do not support constexpr strings and vectors. Add
tests and ifdefs to only use constexpr on selected places for gcc 12+.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
 kms++/inc/kms++/pixelformats.h | 12 ++++++++++--
 meson.build                    | 14 +++++++++++++-
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/kms++/inc/kms++/pixelformats.h b/kms++/inc/kms++/pixelformats.h
index 6049c20..fac9c0f 100644
--- a/kms++/inc/kms++/pixelformats.h
+++ b/kms++/inc/kms++/pixelformats.h
@@ -15,7 +15,12 @@ constexpr uint32_t str_to_fourcc(const std::string_view fourcc)
 	return fourcc[0] | (fourcc[1] << 8) | (fourcc[2] << 16) | (fourcc[3] << 24);
 }
 
-constexpr std::string fourcc_to_str(uint32_t fourcc)
+#if HAS_CONSTEXPR_STR
+constexpr
+#else
+static inline
+#endif
+std::string fourcc_to_str(uint32_t fourcc)
 {
 	char buf[4] = {
 		(char)((fourcc >> 0) & 0xff),
@@ -146,7 +151,10 @@ struct PixelFormatPlaneInfo {
 };
 
 struct PixelFormatInfo {
-	constexpr PixelFormatInfo(const std::string_view name,
+	#if HAS_CONSTEXPR_STR && HAS_CONSTEXPR_VEC
+	constexpr
+	#endif
+	PixelFormatInfo(const std::string_view name,
 	                          const std::string_view drm_fourcc,
 	                          const std::string_view v4l2_4cc,
 				  PixelColorType color,
diff --git a/meson.build b/meson.build
index 9789e8c..cec41f3 100644
--- a/meson.build
+++ b/meson.build
@@ -22,6 +22,18 @@ if cpp.has_argument('-Wno-c99-designator')
     ]
 endif
 
+if cpp.compiles('#include <string>\n constexpr bool test(const std::string& x) { return x.empty(); }')
+    add_global_arguments('-DHAS_CONSTEXPR_STR', language : 'cpp')
+else
+    message('Compiler does not support constexpr strings')
+endif
+
+if cpp.compiles('#include <vector>\n constexpr bool test(const std::vector<int>& x) { return x.empty(); }')
+    add_global_arguments('-DHAS_CONSTEXPR_VEC', language : 'cpp')
+else
+    message('Compiler does not support constexpr vectors')
+endif
+
 add_project_arguments(cpp_arguments, language : 'cpp')
 
 libfmt_dep = dependency('fmt')
@@ -33,7 +45,7 @@ if libdrmomap_dep.found()
 endif
 
 if get_option('libutils')
-	add_global_arguments('-DHAS_KMSXXUTIL', language : 'cpp')
+    add_global_arguments('-DHAS_KMSXXUTIL', language : 'cpp')
 endif
 
 subdir('kms++')
-- 
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