Use "system" include type for all dependencies and add header test

Things get confused when these flags differ across projects, so universally
use "system" for external dependencies and test for header warnings only in
the project that owns them.

3 files changed, 55 insertions, 0 deletions

diff --git a/test/headers/.clang-tidy b/test/headers/.clang-tidy
new file mode 100644
index 0000000..a42a718
--- /dev/null
+++ b/test/headers/.clang-tidy
@@ -0,0 +1,15 @@
+# Copyright 2020-2024 David Robillard <d@drobilla.net>
+# SPDX-License-Identifier: 0BSD OR ISC
+
+Checks: >
+  *,
+  -altera-*,
+  -llvmlibc-*,
+CheckOptions:
+  - key:   readability-function-cognitive-complexity.Threshold
+    value: '1'
+  - key:   readability-identifier-length.IgnoredParameterNames
+    value: '^(a)|(b)|(ui)|(i)$'
+WarningsAsErrors: '*'
+HeaderFilterRegex: '.*'
+FormatStyle: file
diff --git a/test/headers/meson.build b/test/headers/meson.build
new file mode 100644
index 0000000..4415de1
--- /dev/null
+++ b/test/headers/meson.build
@@ -0,0 +1,27 @@
+# Copyright 2020-2025 David Robillard <d@drobilla.net>
+# SPDX-License-Identifier: 0BSD OR ISC
+
+header_c_suppressions = []
+
+if get_option('warning_level') == 'everything'
+  if cc.get_id() == 'clang'
+    if not meson.is_cross_build()
+      header_c_suppressions += ['-Wno-poison-system-directories']
+    endif
+  endif
+endif
+
+if cc.get_id() == 'clang'
+  header_c_suppressions += ['-Wno-nullability-extension']
+endif
+
+test(
+  'headers',
+  executable(
+    'test_headers',
+    files('test_headers.c'),
+    c_args: header_c_suppressions,
+    dependencies: lilv_dep,
+  ),
+  suite: 'unit',
+)
diff --git a/test/headers/test_headers.c b/test/headers/test_headers.c
new file mode 100644
index 0000000..b0d4aa5
--- /dev/null
+++ b/test/headers/test_headers.c
@@ -0,0 +1,13 @@
+// Copyright 2022-2025 David Robillard <d@drobilla.net>
+// SPDX-License-Identifier: ISC
+
+#include <lilv/lilv.h> // IWYU pragma: keep
+
+#ifdef __GNUC__
+__attribute__((const))
+#endif
+int
+main(void)
+{
+  return 0;
+}