Add mojo format to pre-commit/CI and parallelize update_challenges.py (#239)

Wires mojo format into the lint pipeline and applies it repo-wide (78
starter files reformatted). Also parallelizes the HTTP uploads in
scripts/update_challenges.py so deploys fan out instead of running
serially.

- .pre-commit-config.yaml: local mojo-format hook running `mojo format -q`
- .github/workflows/lint.yml: lint-mojo job now installs `modular` via pip
  and enforces formatting via `mojo format` + `git diff --exit-code`
- .github/workflows/create-challenge.yml: adds `modular` to the cron's pip
  install so Claude's `pre-commit run --all-files` step has `mojo` on PATH
- pyproject.toml: drop `target-version = ['py312']` from [tool.black] —
  mblack (which `mojo format` wraps) reads the same section and rejects
  any target above py311; black auto-detects target fine without it
- scripts/update_challenges.py: upload via ThreadPoolExecutor(max_workers=16).
  Loading stays sequential because importlib with a shared "challenge"
  module name and sys.path mutation is not thread-safe.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kunal-mansukhani

.github/workflows/create-challenge.yml

@@ -29,7 +29,7 @@ jobs:
 
       - name: Install dependencies
         run: |
-          pip install pre-commit requests websocket-client
+          pip install pre-commit requests websocket-client modular
           pre-commit install
 
       - name: Fetch open PRs

.github/workflows/lint.yml

@@ -76,6 +76,21 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install Modular (mojo)
+        run: |
+          python -m pip install --upgrade pip
+          pip install modular
+
+      - name: Check Mojo formatting with mojo format
+        run: |
+          find challenges -name "*.mojo" -type f -print0 | xargs -0 mojo format -q
+          git diff --exit-code -- '*.mojo'
+
       - name: Check Mojo files exist and are valid
         run: |
           echo "Checking Mojo files for basic syntax issues..."

.pre-commit-config.yaml

@@ -33,6 +33,15 @@ repos:
         types_or: [c++, c, cuda]
         files: \.(cu|cpp|h)$
 
+  # Mojo formatting
+  - repo: local
+    hooks:
+      - id: mojo-format
+        name: mojo format
+        entry: mojo format -q
+        language: system
+        files: \.mojo$
+
   # General file checks
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v4.5.0

challenges/easy/19_reverse_array/starter/starter.mojo

@@ -3,9 +3,11 @@ from std.gpu import block_dim, block_idx, thread_idx
 from std.memory import UnsafePointer
 from std.math import ceildiv
 
+
 fn reverse_array_kernel(input: UnsafePointer[Float32, MutExternalOrigin], N: Int32):
     pass
 
+
 # input is a device pointer (i.e. pointer to memory on the GPU)
 @export
 fn solve(input: UnsafePointer[Float32, MutExternalOrigin], N: Int32) raises:
@@ -15,10 +17,6 @@ fn solve(input: UnsafePointer[Float32, MutExternalOrigin], N: Int32) raises:
     var blocksPerGrid = ceildiv(N, threadsPerBlock)
 
     var _kernel = ctx.compile_function[reverse_array_kernel, reverse_array_kernel]()
-    ctx.enqueue_function(_kernel,
-        input, N,
-        grid_dim = blocksPerGrid,
-        block_dim = threadsPerBlock
-    )
+    ctx.enqueue_function(_kernel, input, N, grid_dim=blocksPerGrid, block_dim=threadsPerBlock)
 
     ctx.synchronize()

challenges/easy/1_vector_add/starter/starter.mojo

@@ -3,21 +3,29 @@ from std.gpu import block_dim, block_idx, thread_idx
 from std.memory import UnsafePointer
 from std.math import ceildiv
 
-fn vector_add_kernel(A: UnsafePointer[Float32, MutExternalOrigin], B: UnsafePointer[Float32, MutExternalOrigin], C: UnsafePointer[Float32, MutExternalOrigin], N: Int32):
+
+fn vector_add_kernel(
+    A: UnsafePointer[Float32, MutExternalOrigin],
+    B: UnsafePointer[Float32, MutExternalOrigin],
+    C: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+):
     pass
 
+
 # A, B, C are device pointers (i.e. pointers to memory on the GPU)
 @export
-fn solve(A: UnsafePointer[Float32, MutExternalOrigin], B: UnsafePointer[Float32, MutExternalOrigin], C: UnsafePointer[Float32, MutExternalOrigin], N: Int32) raises:
+fn solve(
+    A: UnsafePointer[Float32, MutExternalOrigin],
+    B: UnsafePointer[Float32, MutExternalOrigin],
+    C: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+) raises:
     var BLOCK_SIZE: Int32 = 256
     var ctx = DeviceContext()
     var num_blocks = ceildiv(N, BLOCK_SIZE)
 
     var _kernel = ctx.compile_function[vector_add_kernel, vector_add_kernel]()
-    ctx.enqueue_function(_kernel,
-        A, B, C, N,
-        grid_dim  = num_blocks,
-        block_dim = BLOCK_SIZE
-    )
+    ctx.enqueue_function(_kernel, A, B, C, N, grid_dim=num_blocks, block_dim=BLOCK_SIZE)
 
     ctx.synchronize()

challenges/easy/21_relu/starter/starter.mojo

@@ -3,22 +3,30 @@ from std.gpu import block_dim, block_idx, thread_idx
 from std.memory import UnsafePointer
 from std.math import ceildiv
 
-fn relu_kernel(input: UnsafePointer[Float32, MutExternalOrigin], output: UnsafePointer[Float32, MutExternalOrigin], N: Int32):
+
+fn relu_kernel(
+    input: UnsafePointer[Float32, MutExternalOrigin],
+    output: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+):
     pass
 
+
 # input, output are device pointers (i.e. pointers to memory on the GPU)
 @export
-fn solve(input: UnsafePointer[Float32, MutExternalOrigin], output: UnsafePointer[Float32, MutExternalOrigin], N: Int32) raises:
+fn solve(
+    input: UnsafePointer[Float32, MutExternalOrigin],
+    output: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+) raises:
     var threadsPerBlock: Int32 = 256
     var ctx = DeviceContext()
 
     var blocksPerGrid = ceildiv(N, threadsPerBlock)
 
     var _kernel = ctx.compile_function[relu_kernel, relu_kernel]()
-    ctx.enqueue_function(_kernel,
-        input, output, N,
-        grid_dim = blocksPerGrid,
-        block_dim = threadsPerBlock
+    ctx.enqueue_function(
+        _kernel, input, output, N, grid_dim=blocksPerGrid, block_dim=threadsPerBlock
     )
 
     ctx.synchronize()

challenges/easy/23_leaky_relu/starter/starter.mojo

@@ -3,22 +3,30 @@ from std.gpu import block_dim, block_idx, thread_idx
 from std.memory import UnsafePointer
 from std.math import ceildiv
 
-fn leaky_relu_kernel(input: UnsafePointer[Float32, MutExternalOrigin], output: UnsafePointer[Float32, MutExternalOrigin], N: Int32):
+
+fn leaky_relu_kernel(
+    input: UnsafePointer[Float32, MutExternalOrigin],
+    output: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+):
     pass
 
+
 # input, output are device pointers (i.e. pointers to memory on the GPU)
 @export
-fn solve(input: UnsafePointer[Float32, MutExternalOrigin], output: UnsafePointer[Float32, MutExternalOrigin], N: Int32) raises:
+fn solve(
+    input: UnsafePointer[Float32, MutExternalOrigin],
+    output: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+) raises:
     var threadsPerBlock: Int32 = 256
     var ctx = DeviceContext()
 
     var blocksPerGrid = ceildiv(N, threadsPerBlock)
 
     var _kernel = ctx.compile_function[leaky_relu_kernel, leaky_relu_kernel]()
-    ctx.enqueue_function(_kernel,
-        input, output, N,
-        grid_dim = blocksPerGrid,
-        block_dim = threadsPerBlock
+    ctx.enqueue_function(
+        _kernel, input, output, N, grid_dim=blocksPerGrid, block_dim=threadsPerBlock
     )
 
     ctx.synchronize()

challenges/easy/24_rainbow_table/starter/starter.mojo

@@ -3,6 +3,7 @@ from std.gpu import block_dim, block_idx, thread_idx
 from std.memory import UnsafePointer
 from std.math import ceildiv
 
+
 fn fnv1a_hash(input: Int32) -> UInt32:
     alias FNV_PRIME: UInt32 = 16777619
     alias OFFSET_BASIS: UInt32 = 2166136261
@@ -15,23 +16,32 @@ fn fnv1a_hash(input: Int32) -> UInt32:
 
     return hash
 
-fn fnv1a_hash_kernel(input: UnsafePointer[Int32, MutExternalOrigin], output: UnsafePointer[UInt32, MutExternalOrigin],
-                     N: Int32, R: Int32):
+
+fn fnv1a_hash_kernel(
+    input: UnsafePointer[Int32, MutExternalOrigin],
+    output: UnsafePointer[UInt32, MutExternalOrigin],
+    N: Int32,
+    R: Int32,
+):
     pass
 
+
 # input, output are device pointers (i.e. pointers to memory on the GPU)
 @export
-fn solve(input: UnsafePointer[Int32, MutExternalOrigin], output: UnsafePointer[UInt32, MutExternalOrigin], N: Int32, R: Int32) raises:
+fn solve(
+    input: UnsafePointer[Int32, MutExternalOrigin],
+    output: UnsafePointer[UInt32, MutExternalOrigin],
+    N: Int32,
+    R: Int32,
+) raises:
     var threadsPerBlock: Int32 = 256
     var ctx = DeviceContext()
 
     var blocksPerGrid = ceildiv(N, threadsPerBlock)
 
     var _kernel = ctx.compile_function[fnv1a_hash_kernel, fnv1a_hash_kernel]()
-    ctx.enqueue_function(_kernel,
-        input, output, N, R,
-        grid_dim = blocksPerGrid,
-        block_dim = threadsPerBlock
+    ctx.enqueue_function(
+        _kernel, input, output, N, R, grid_dim=blocksPerGrid, block_dim=threadsPerBlock
     )
 
     ctx.synchronize()

challenges/easy/2_matrix_multiplication/starter/starter.mojo

@@ -3,23 +3,45 @@ from std.gpu import block_dim, block_idx, thread_idx
 from std.memory import UnsafePointer
 from std.math import ceildiv
 
-fn matrix_multiplication_kernel(A: UnsafePointer[Float32, MutExternalOrigin], B: UnsafePointer[Float32, MutExternalOrigin], C: UnsafePointer[Float32, MutExternalOrigin], M: Int32, N: Int32, K: Int32):
+
+fn matrix_multiplication_kernel(
+    A: UnsafePointer[Float32, MutExternalOrigin],
+    B: UnsafePointer[Float32, MutExternalOrigin],
+    C: UnsafePointer[Float32, MutExternalOrigin],
+    M: Int32,
+    N: Int32,
+    K: Int32,
+):
     pass
 
+
 # A, B, C are device pointers (i.e. pointers to memory on the GPU)
 @export
-fn solve(A: UnsafePointer[Float32, MutExternalOrigin], B: UnsafePointer[Float32, MutExternalOrigin], C: UnsafePointer[Float32, MutExternalOrigin], M: Int32, N: Int32, K: Int32) raises:
+fn solve(
+    A: UnsafePointer[Float32, MutExternalOrigin],
+    B: UnsafePointer[Float32, MutExternalOrigin],
+    C: UnsafePointer[Float32, MutExternalOrigin],
+    M: Int32,
+    N: Int32,
+    K: Int32,
+) raises:
     var BLOCK_SIZE: Int32 = 16
     var ctx = DeviceContext()
 
     var grid_dim_x = ceildiv(K, BLOCK_SIZE)
     var grid_dim_y = ceildiv(M, BLOCK_SIZE)
 
     var _kernel = ctx.compile_function[matrix_multiplication_kernel, matrix_multiplication_kernel]()
-    ctx.enqueue_function(_kernel,
-        A, B, C, M, N, K,
-        grid_dim = (grid_dim_x, grid_dim_y),
-        block_dim = (BLOCK_SIZE, BLOCK_SIZE)
+    ctx.enqueue_function(
+        _kernel,
+        A,
+        B,
+        C,
+        M,
+        N,
+        K,
+        grid_dim=(grid_dim_x, grid_dim_y),
+        block_dim=(BLOCK_SIZE, BLOCK_SIZE),
     )
 
     ctx.synchronize()

challenges/easy/31_matrix_copy/starter/starter.mojo

@@ -3,23 +3,29 @@ from std.gpu import block_dim, block_idx, thread_idx
 from std.memory import UnsafePointer
 from std.math import ceildiv
 
-fn copy_matrix_kernel(A: UnsafePointer[Float32, MutExternalOrigin], B: UnsafePointer[Float32, MutExternalOrigin], N: Int32):
+
+fn copy_matrix_kernel(
+    A: UnsafePointer[Float32, MutExternalOrigin],
+    B: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+):
     pass
 
+
 # A, B are device pointers (i.e. pointers to memory on the GPU)
 @export
-fn solve(A: UnsafePointer[Float32, MutExternalOrigin], B: UnsafePointer[Float32, MutExternalOrigin], N: Int32) raises:
+fn solve(
+    A: UnsafePointer[Float32, MutExternalOrigin],
+    B: UnsafePointer[Float32, MutExternalOrigin],
+    N: Int32,
+) raises:
     var total = N * N
     var threadsPerBlock: Int32 = 256
     var ctx = DeviceContext()
 
     var blocksPerGrid = ceildiv(total, threadsPerBlock)
 
     var _kernel = ctx.compile_function[copy_matrix_kernel, copy_matrix_kernel]()
-    ctx.enqueue_function(_kernel,
-        A, B, N,
-        grid_dim = blocksPerGrid,
-        block_dim = threadsPerBlock
-    )
+    ctx.enqueue_function(_kernel, A, B, N, grid_dim=blocksPerGrid, block_dim=threadsPerBlock)
 
     ctx.synchronize()