ninja

Name: ninja
Author: mohitmishra786

316installs19forks

How to install ninja?

mohitmishra786/low-level-dev-skills/ninja

$npx -y skills add mohitmishra786/low-level-dev-skills --skill ninja

Installs into the current project.

Summary

Ninja build system skill. Use when diagnosing Ninja build failures, understanding Ninja's role as a low-level build executor generated by CMake or other meta-build systems, tuning parallelism, interpreting Ninja output, or working with build.ninja files. Activates on queries abou

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SKILL.md

1	# Ninja
2
3	## Purpose
4
5	Guide agents through Ninja as a build executor: diagnosing failures, controlling parallelism, generating from CMake, and understanding the `.ninja` file format when needed.
6
7	## Triggers
8
9	- "Ninja is failing — how do I get more output?"
10	- "How do I use Ninja with CMake?"
11	- "How many parallel jobs does Ninja use?"
12	- "How do I add a custom build step in Ninja?"
13	- "What is a `build.ninja` file?"
14
15	## Workflow
16
17	### 1. Ninja as a CMake generator
18
19	The most common use of Ninja is as the build executor for CMake:
20
21	```bash
22	# Configure with Ninja
23	cmake -S . -B build -G Ninja
24	cmake --build build # uses ninja internally
25
26	# Or invoke ninja directly
27	cd build && ninja
28
29	# Specify parallelism
30	ninja -j4
31	ninja -j$(nproc)
32
33	# Build specific target
34	ninja myapp
35	ninja install
36	```
37
38	CMake also supports `Ninja Multi-Config`:
39
40	```bash
41	cmake -S . -B build -G "Ninja Multi-Config"
42	cmake --build build --config Release
43	cmake --build build --config Debug
44	```
45
46	### 2. Verbose output and diagnostics
47
48	```bash
49	# Show full commands (not just [CC] foo.c)
50	ninja -v
51
52	# Dry run (show what would be built)
53	ninja -n
54
55	# Show why a target needs rebuilding
56	ninja -d explain myapp
57
58	# Print all targets
59	ninja -t targets all
60
61	# Print targets grouped by rule
62	ninja -t targets rule cc
63
64	# Dependency graph (graphviz)
65	ninja -t graph myapp \| dot -Tsvg -o deps.svg
66	```
67
68	### 3. Common Ninja flags
69
70	\| Flag \| Effect \|
71	\|------\|--------\|
72	\| `-j N` \| Parallel jobs (default: CPUs + 2) \|
73	\| `-l N` \| Don't start new jobs if load average > N \|
74	\| `-k N` \| Keep going after N failures (default 1) \|
75	\| `-v` \| Verbose: show full command lines \|
76	\| `-n` \| Dry run \|
77	\| `-C dir` \| Change to `dir` before doing anything \|
78	\| `-t tool` \| Run a sub-tool (`clean`, `query`, `targets`, `graph`, `compdb`) \|
79
80	### 4. Cleaning
81
82	```bash
83	ninja -t clean # remove build outputs
84	ninja -t clean -g # also remove generated files
85	```
86
87	Or via CMake:
88
89	```bash
90	cmake --build build --target clean
91	```
92
93	### 5. compile_commands.json
94
95	Ninja (via CMake) can generate a `compile_commands.json` for IDE integration and `clang-tidy`:
96
97	```bash
98	cmake -S . -B build -G Ninja -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
99	ln -sf build/compile_commands.json .
100	```
101
102	### 6. build.ninja format (reference)
103
104	Rarely hand-written, but useful to understand for debugging:
105
106	```ninja
107	# Variable
108	cflags = -Wall -O2
109
110	# Rule
111	rule cc
112	command = gcc $cflags -c $in -o $out
113	description = CC $in
114
115	# Build edge
116	build foo.o: cc foo.c
117
118	# Phony target
119	build all: phony foo.o
120
121	# Default target
122	default all
123	```
124
125	Key concepts:
126
127	- `rule`: defines how to produce outputs from inputs
128	- `build`: instantiates a rule with specific files
129	- `$in` / `$out`: automatic variables for inputs/outputs
130	- `phony`: a target that is always considered out of date (like `.PHONY` in make)
131
132	### 7. Ninja sub-tools
133
134	```bash
135	# List all build targets
136	ninja -t targets
137
138	# Query dependencies of a target
139	ninja -t query myapp
140
141	# Clean (already mentioned)
142	ninja -t clean
143
144	# Generate compile_commands.json (if supported by generator)
145	ninja -t compdb cc cxx > compile_commands.json
146
147	# List rules
148	ninja -t rules
149	```
150
151	### 8. Common issues
152
153	\| Issue \| Cause \| Fix \|
154	\|-------\|-------\|-----\|
155	\| `ninja: error: 'foo.o', needed by 'prog', missing and no known rule to make it` \| Missing build rule \| Regenerate with CMake; check `add_executable` source list \|
156	\| Build not picking up changes \| Stale `build.ninja` \| Re-run `cmake -S . -B build` \|
157	\| Very slow parallel build \| `-j` too high for I/O-bound build \| Use `-l$(nproc)` to limit by load \|
158	\| Circular dependency \| Rule depends on itself \| Check CMake target dependencies \|
159
160	For the full Ninja command reference, `build.ninja` format details, and CMake integration patterns, see [references/cheatsheet.md](references/cheatsheet.md).
161
162	## Related skills
163
164	- Use `skills/build-systems/cmake` for CMake configuration that generates Ninja files
165	- Use `skills/build-systems/make` for Make-based projects

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ninja

316installs19forks

View on GitHub

How to install ninja?

mohitmishra786/low-level-dev-skills/ninja

$npx -y skills add mohitmishra786/low-level-dev-skills --skill ninja

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Ninja
2
3	## Purpose
4
5	Guide agents through Ninja as a build executor: diagnosing failures, controlling parallelism, generating from CMake, and understanding the `.ninja` file format when needed.
6
7	## Triggers
8
9	- "Ninja is failing — how do I get more output?"
10	- "How do I use Ninja with CMake?"
11	- "How many parallel jobs does Ninja use?"
12	- "How do I add a custom build step in Ninja?"
13	- "What is a `build.ninja` file?"
14
15	## Workflow
16
17	### 1. Ninja as a CMake generator
18
19	The most common use of Ninja is as the build executor for CMake:
20
21	```bash
22	# Configure with Ninja
23	cmake -S . -B build -G Ninja
24	cmake --build build # uses ninja internally
25
26	# Or invoke ninja directly
27	cd build && ninja
28
29	# Specify parallelism
30	ninja -j4
31	ninja -j$(nproc)
32
33	# Build specific target
34	ninja myapp
35	ninja install
36	```
37
38	CMake also supports `Ninja Multi-Config`:
39
40	```bash
41	cmake -S . -B build -G "Ninja Multi-Config"
42	cmake --build build --config Release
43	cmake --build build --config Debug
44	```
45
46	### 2. Verbose output and diagnostics
47
48	```bash
49	# Show full commands (not just [CC] foo.c)
50	ninja -v
51
52	# Dry run (show what would be built)
53	ninja -n
54
55	# Show why a target needs rebuilding
56	ninja -d explain myapp
57
58	# Print all targets
59	ninja -t targets all
60
61	# Print targets grouped by rule
62	ninja -t targets rule cc
63
64	# Dependency graph (graphviz)
65	ninja -t graph myapp \| dot -Tsvg -o deps.svg
66	```
67
68	### 3. Common Ninja flags
69
70	\| Flag \| Effect \|
71	\|------\|--------\|
72	\| `-j N` \| Parallel jobs (default: CPUs + 2) \|
73	\| `-l N` \| Don't start new jobs if load average > N \|
74	\| `-k N` \| Keep going after N failures (default 1) \|
75	\| `-v` \| Verbose: show full command lines \|
76	\| `-n` \| Dry run \|
77	\| `-C dir` \| Change to `dir` before doing anything \|
78	\| `-t tool` \| Run a sub-tool (`clean`, `query`, `targets`, `graph`, `compdb`) \|
79
80	### 4. Cleaning
81
82	```bash
83	ninja -t clean # remove build outputs
84	ninja -t clean -g # also remove generated files
85	```
86
87	Or via CMake:
88
89	```bash
90	cmake --build build --target clean
91	```
92
93	### 5. compile_commands.json
94
95	Ninja (via CMake) can generate a `compile_commands.json` for IDE integration and `clang-tidy`:
96
97	```bash
98	cmake -S . -B build -G Ninja -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
99	ln -sf build/compile_commands.json .
100	```
101
102	### 6. build.ninja format (reference)
103
104	Rarely hand-written, but useful to understand for debugging:
105
106	```ninja
107	# Variable
108	cflags = -Wall -O2
109
110	# Rule
111	rule cc
112	command = gcc $cflags -c $in -o $out
113	description = CC $in
114
115	# Build edge
116	build foo.o: cc foo.c
117
118	# Phony target
119	build all: phony foo.o
120
121	# Default target
122	default all
123	```
124
125	Key concepts:
126
127	- `rule`: defines how to produce outputs from inputs
128	- `build`: instantiates a rule with specific files
129	- `$in` / `$out`: automatic variables for inputs/outputs
130	- `phony`: a target that is always considered out of date (like `.PHONY` in make)
131
132	### 7. Ninja sub-tools
133
134	```bash
135	# List all build targets
136	ninja -t targets
137
138	# Query dependencies of a target
139	ninja -t query myapp
140
141	# Clean (already mentioned)
142	ninja -t clean
143
144	# Generate compile_commands.json (if supported by generator)
145	ninja -t compdb cc cxx > compile_commands.json
146
147	# List rules
148	ninja -t rules
149	```
150
151	### 8. Common issues
152
153	\| Issue \| Cause \| Fix \|
154	\|-------\|-------\|-----\|
155	\| `ninja: error: 'foo.o', needed by 'prog', missing and no known rule to make it` \| Missing build rule \| Regenerate with CMake; check `add_executable` source list \|
156	\| Build not picking up changes \| Stale `build.ninja` \| Re-run `cmake -S . -B build` \|
157	\| Very slow parallel build \| `-j` too high for I/O-bound build \| Use `-l$(nproc)` to limit by load \|
158	\| Circular dependency \| Rule depends on itself \| Check CMake target dependencies \|
159
160	For the full Ninja command reference, `build.ninja` format details, and CMake integration patterns, see [references/cheatsheet.md](references/cheatsheet.md).
161
162	## Related skills
163
164	- Use `skills/build-systems/cmake` for CMake configuration that generates Ninja files
165	- Use `skills/build-systems/make` for Make-based projects

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