Android C/C++ source files can be checked by clang-tidy for issues like coding style, error-prone/performance patterns, and static flow analysis. See the official clang-tidy document and list of clang-tidy checks.
The simplest way to enable clang-tidy checks is to set environment variable WITH_TIDY
.
$ WITH_TIDY=1 make
This will turn on the global default to run clang-tidy for every required C/C++ source file compilation. The global default clang-tidy checks do not include time-consuming static analyzer checks. To enable those checks, set the CLANG_ANALYZER_CHECKS
variable.
$ WITH_TIDY=1 CLANG_ANALYZER_CHECKS=1 make
The default global clang-tidy checks and flags are defined in build/soong/cc/config/tidy.go.
The global default can be overwritten by module properties in Android.bp.
tidy
and tidy_checks
For example, in system/bpf/Android.bp, clang-tidy is enabled explicitly and with a different check list:
cc_defaults { name: "bpf_defaults", // snipped tidy: true, tidy_checks: [ "android-*", "cert-*", "-cert-err34-c", "clang-analyzer-security*", // Disabling due to many unavoidable warnings from POSIX API usage. "-google-runtime-int", ], }
That means in normal builds, even without WITH_TIDY=1
, the modules that use bpf_defaults
will run clang-tidy over C/C++ source files with the given tidy_checks
. Note that clang-analyzer-security*
is included in tidy_checks
but not all clang-analyzer-*
checks. Check cert-err34-c
is disabled, although cert-*
is selected.
Some modules might want to disable clang-tidy even when environment variable WITH_TIDY=1
is set. Examples can be found in system/netd/tests/Android.bp
cc_test { name: "netd_integration_test", // snipped defaults: ["netd_defaults"], tidy: false, // cuts test build time by almost 1 minute
and in bionic/tests/Android.bp.
cc_test_library { name: "fortify_disabled_for_tidy", // snipped srcs: ["clang_fortify_tests.cpp"], tidy: false, }
tidy_checks_as_errors
The global tidy checks are enabled as warnings. If a C/C++ module wants to be free of certain clang-tidy warnings, it can chose those checks to be treated as errors. For example system/core/libsysutils/Android.bp has enabled clang-tidy explicitly, selected its own tidy checks, and set three groups of tidy checks as errors:
cc_library { name: "libsysutils", // snipped tidy: true, tidy_checks: [ "-*", "cert-*", "clang-analyzer-security*", "android-*", ], tidy_checks_as_errors: [ "cert-*", "clang-analyzer-security*", "android-*", ], // snipped }
tidy_flags
and tidy_disabled_srcs
Extra clang-tidy flags can be passed with the tidy_flags
property.
Some Android modules use the tidy_flags
to pass “-warnings-as-errors=” to clang-tidy. This usage should now be replaced with the tidy_checks_as_errors
property.
Some other tidy flags examples are -format-style=
and -header-filter=
For example, in art/odrefresh/Android.bp, we found
cc_defaults { name: "odrefresh-defaults", srcs: [ "odrefresh.cc", "odr_common.cc", "odr_compilation_log.cc", "odr_fs_utils.cc", "odr_metrics.cc", "odr_metrics_record.cc", ], // snipped generated_sources: [ "apex-info-list-tinyxml", "art-apex-cache-info", "art-odrefresh-operator-srcs", ], // snipped tidy: true, tidy_disabled_srcs: [":art-apex-cache-info"], tidy_flags: [ "-format-style=file", "-header-filter=(art/odrefresh/|system/apex/)", ], }
That means all modules with the odrefresh-defaults
will have clang-tidy enabled, but not for generated source files in art-apex-cache-info
. The clang-tidy is called with extra flags to specify the format-style and header-filter.
Note that the globally set default for header-filter is to include only the module directory. So, the default clang-tidy warnings for art/odrefresh
modules will include source files under that directory. Now odrefresh-defaults
is interested in seeing warnings from both art/odrefresh/
and system/apex/
and it redefines -header-filter
in its tidy_flags
.
Setting WITH_TIDY=1
is easy to enable clang-tidy globally for any build. However, it adds extra compilation time.
For developers focusing on just one directory, they only want to compile their files with clang-tidy and wish to build other Android components as fast as possible. Changing the WITH_TIDY=1
variable setting is also expensive since the build.ninja file will be regenerated due to any such variable change.
To manually select only some directories or modules to compile with clang-tidy, do not set the WITH_TIDY=1
variable, but use the special tidy-<directory>
phony target. For example, a person working on system/libbase
can build Android quickly with
unset WITH_TIDY # Optional, not if you haven't set WITH_TIDY make droid tidy-system-libbase
For any directory d1/d2/d3
, a phony target tidy-d1-d2-d3 is generated if there is any C/C++ source file under d1/d2/d3
.
Note that with make droid tidy-system-libbase
, some C/C++ files that are not needed by the droid
target will be passed to clang-tidy if they are under system/libbase
. This is like a checkbuild
under system/libbase
to include all modules, but only C/C++ files of those modules are compiled with clang-tidy.
A special tidy-soong
target is defined to include all C/C++ source files in all directories. This phony target is sometimes used to test if all source files compile with a new clang-tidy release.
A subset of each tidy-* phony target is defined to reduce test time. Since any Android module, a C/C++ library or binary, can be built for many different variants, one C/C++ source file is usually compiled multiple times with different compilation flags. Many of such variant flags have little or no effect on clang-tidy checks. To reduce clang-tidy check time, a subset target like tidy-soong_subset
or tidy-system-libbase_subset
is generated to include only a subset, the first variant, of each module in the directory.
Hence, for C/C++ source code quality, instead of a long “make checkbuild”, we can use “make tidy-soong_subset”.
Some Android modules have large files that take a long time to compile with clang-tidy, with or without the clang-analyzer checks. To limit clang-tidy time, an environment variable can be set as
WITH_TIDY=1 TIDY_TIMEOUT=90 make
This 90-second limit is actually the default time limit in several Android continuous builds where WITH_TIDY=1
and CLANG_ANALYZER_CHECKS=1
are set.
Some of the previously mentioned features are defined only for modules in Android.bp files, not for Android.mk modules yet.
The global WITH_TIDY=1
variable will enable clang-tidy for all C/C++ modules in Android.bp or Android.mk files.
The global TIDY_TIMEOUT
variable is recognized by Android prebuilt clang-tidy, so it should work for any clang-tidy invocation.
The clang-tidy module level properties are defined for Android.bp modules. For Android.mk modules, old LOCAL_TIDY
, LOCAL_TIDY_CHECKS
, LOCAL_TIDY_FLAGS
work similarly, but it would be better to convert those modules to use Android.bp files.
The tidy-*
phony targets are only generated for Android.bp modules.