tools/gn/docs/check.md - Issue 2647443003: Remove obsolete GN check.md documentation.

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Issue 2647443003: Remove obsolete GN check.md documentation. (Closed)

Patch Set: Created 3 years, 11 months ago

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1 # GN Check

2

3 GN has several different ways to check dependencies. Many of them are checked by

4 the `gn check` command. Running checks involve opening and scanning all source

5 files so this isn't run every time a build is updated. To run check on an

6 existing build:

7

8 gn check out/mybuild

9

10 To run the check as part of the "gen" command to update the build (this is what

11 the bots do):

12

13 gn gen out/mybuild --check

14

15 [TOC]

16

17 ## Concepts

18

19 ### Visibility

20

21 Targets can control which other targets may depend on them by specifying

22 `visibility`. Visibility is always checked when running any GN command (not just

23 `gn check`.

24

25 By default, targets are "public" meaning any target can depend on them. If you

26 supply a list, visibility will be listed to those targets (possibly including

27 wildcards):

28

29 ```

30 visibility = [

31 ":*", # All targets in this file.

32 "//content/*", # All targets in content and any subdirectory thereof.

33 "//tools:doom_melon", # This specific target.

34 ]

35 ```

36

37 See `gn help visibility` for more details and examples.

38

39 ### Public header files

40

41 Targets can control which headers may be included by dependent targets so as to

42 define a public API. If your target specifies only `sources`, then all headers

43 listed there are public and can be included by all dependents.

44

45 If your target defines a `public` variable, only the files listed in that list

46 will be public. Files in `sources` but not `public` (they can be in both or only

47 one) may not be included by dependent targets.

48

49 ```

50 source_set("foo") {

51 public = [

52 "foo.h",

53 "foo_config.h",

54 ]

55 sources = [

56 "foo.cc",

57 "foo.h",

58 "bar.cc",

59 "bar.h",

60 ]

61 }

62 ```

63

64 ### Public dependencies

65

66 In order to include files from your target, that target must be listed in your

67 target's dependencies. By default, transitively depending on a target doesn't

68 give your files this privilege.

69

70 If a target exposes a dependency as part of its public API, then it can list

71 that dependency as a `public_deps`:

72

73 ```

74 source_set("foo") {

75 sources = [ ... ]

76 public_deps = [

77 "//base",

78 ]

79 deps = [

80 "//tools/doom_melon",

81 ]

82 }

83 ```

84

85 Targets that depend on `foo` can include files from `base` but not from

86 `doom_melon`. To include public headers from `doom\_melon, a target would need

87 to depend directly on it.

88

89 Public dependencies work transitively, so listing a target as a public

90 dependency also exposes that target's public dependencies. Along with the

91 ability to include headers, public dependencies forward the `public_configs`

92 which allow settings like defines and include directories to apply to

93 dependents.

94

95 ## Putting it all together

96

97 In order to include a header from target Y in a file that is part of target X:

98

99 * X must be in Y's `visibility` list (or B must have no `visibility` defined).

100 * The header must be in Y's `public` headers (or Y must have no `public`

101 variable defined).

102 * X must depend directly on Y, or there must be a path from X to Y following

103 only public dependencies.

104

105 ### What gets checked

106

107 Chrome currently doesn't come close to passing a `gn check` pass. You can check

108 specific targets or subtrees for issues:

109

110 gn check out/mybuild //base

111

112 gn check out/mybuild "//mojo/*"

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