State of warnings in CI `develop`

[Becheler]

Compiler warnings (global, full CI matrix)

Source: CI run 26759013540 on develop (push, sha 6efc6b60, 2026-06-01). All 24 jobs succeeded; the counts below are warnings, not errors.

Per-job warning counts

Job	Warnings
windows_msvc_14_3 (msvc-14.3)	1226
macos (clang, 14)	88
macos (clang, 17)	83
macos (clang, 20)	83
ubuntu (clang-19, 14/17/20/23)	76 each
ubuntu (gcc-14, 14/17/20/23)	52 each
all *-cmake-install / *-cmake-subdir jobs	0

The cmake jobs build only the library, so they surface nothing. All warnings come from the b2 toolset jobs that also build tests and examples. Counts are stable across language-standard variants (14/17/20/23), so the standard level does not change the warning set.

Correctness-relevant (fix or investigate, do not just silence)

File:line	Warning	Compilers
detail/adjacency_list.hpp:2276	variable p used uninitialized / passed as uninitialized const reference	clang (-Wuninitialized-const-reference) and gcc (-Wmaybe-uninitialized)
test/r_c_shortest_paths_test.cpp:160, :264	possibly dangling reference to a temporary	gcc (-Wdangling-reference)
example/r_c_shortest_paths_example.cpp:158	possibly dangling reference to a temporary	gcc (-Wdangling-reference)
pending/detail/disjoint_sets.hpp:58, :59	signed/unsigned comparison	gcc (-Wsign-compare)

adjacency_list.hpp:2276 is the strongest signal: two independent compilers agree p may be read before initialization.

Cosmetic clang/gcc warnings (dead code / deprecation)

Library headers:

File:line	Warning	Flag
howard_cycle_ratio.hpp:360	lambda capture this not used	-Wunused-lambda-capture
r_c_shortest_paths.hpp:200	unused typedef LTraits	-Wunused-local-typedef(s)
louvain_clustering.hpp:58, :226, :529	unused type aliases	-Wunused-local-typedef(s)
louvain_clustering.hpp:243, :403, :558	pass_number / iteration set but not used	-Wunused-but-set-variable

Tests:

File:line	Warning	Flag
test/graph.cpp:159, test/property_iter.cpp:63, test/csr_graph_test.cpp:328	variable set but not used	-Wunused-but-set-variable
test/isomorphism.cpp:89, :308, test/vf2_sub_graph_iso_test.cpp:80	std::random_shuffle deprecated, use std::shuffle	-Wdeprecated-declarations
test/min_degree_empty.cpp:40	signed/unsigned comparison	-Wsign-compare

Examples:

File:line	Warning	Flag
example/graph-assoc-types.cpp:16-20, example/quick-tour.cpp:34	unused type aliases	-Wunused-local-typedef(s)
example/minimum_degree_ordering.cpp:45, example/two_graphs_common_spanning_trees.cpp:57	unused variable	-Wunused-variable
example/fibonacci_heap.cpp:44	signed/unsigned comparison	-Wsign-compare
example/fibonacci_heap.cpp:47	std::random_shuffle deprecated	-Wdeprecated-declarations

clang/gcc flag totals (raw occurrences across all unix jobs)

Flag	Count
-Wunused-but-set-variable	259
-Wunused-local-typedef(s)	126 + 108
-Wunused-lambda-capture	77
-Wdeprecated-declarations	45
-Wsign-compare	24
-Wunused-variable	22
-Wmaybe-uninitialized	20
-Wuninitialized-const-reference	14
-Wdangling-reference	12

MSVC (msvc-14.3): 1226 warnings, 162 distinct sites

Dominated by numeric conversion warnings that the gcc/clang matrix mostly does not emit:

Code	Meaning	Count
C4267	conversion from size_t, possible loss of data	836
C4305	truncation (e.g. double to float)	198
C4244	conversion, possible loss of data	162
C4101	unreferenced local variable	15
C4996	sscanf etc. deemed unsafe (CRT)	9
C4146	unary minus on unsigned type	6

Top files by MSVC warning count:

File	Count
property_map.hpp	150
random.hpp	132
minimum_degree_ordering.hpp	120
king_ordering.hpp	72
isomorphism.hpp	45
bandwidth.hpp	36
disjoint_sets.hpp	30
(plus astar/quick_tour/bellman-ford examples via C4305)	many

These are long-standing size_t to int / float-truncation issues in core headers. They are mostly benign on LP64 but real on MSVC's data model, and are the bulk of the project's total warning volume.

Takeaways

• Almost all of the gcc/clang noise is dead-code lint, cheap to clear.
• Three correctness-class items deserve real review: the uninitialized p in adjacency_list.hpp, the dangling references in r_c_shortest_paths, and the signed/unsigned comparisons in disjoint_sets.hpp.
• MSVC conversion warnings are by far the largest group and a separate, larger cleanup effort focused on property_map.hpp, random.hpp, and the ordering headers.

[jeremy-murphy]

I essentially consider -Wall -Wextra to be non-negotiable, if thanks helps. :)