---
sidebar_label: Build system
---

# Build System

## Compiler Backends

DCR supports 4 compilation backends. Selection is automatic based on file extension.

| Backend | Files | When used |
|---------|-------|-----------|
| `unix_cc` | `.c`, `.cpp`, `.cxx`, `.cc`, `.S` | gcc/clang on Linux/macOS/BSD |
| `msvc` | `.c`, `.cpp`, `.cxx`, `.cc` | Windows (cl, clang-cl) |
| `gas` | `.s` | ARM/ARM64 assembler (no preprocessor) |
| `nasm` | `.asm` | x86/x86_64 assembler |

### Unix CC

- Compiler resolved via `resolve_compiler()`: `DCR_COMPILER` > `DCR_CC` > `[toolchain]` > `build.compiler` > `PATH`
- Supports `.d` files for header dependency tracking
- Flags: `-std=`, `-MMD -MF`, `-c -o`, `-I`, `-L`, `-l`
- Conditional flags based on config:
  - `freestanding` or bare-metal target: `-ffreestanding` (compile), `-nostdlib -static` (link)
  - `lto`: `-flto` (compile + link)
  - `panic = "abort"`: `-fno-exceptions` (C++ only), `-fno-unwind-tables`, `-fno-asynchronous-unwind-tables`

### MSVC

- Supports cl.exe and clang-cl.exe
- Flags: `/std:`, `/Fo:`, `/Fe:`, `/I`, `/link`

### GAS / NASM

- GAS: `-I`, `-c -o`, `--defsym`
- NASM: `-I`, `-o`, `-D`, `-f` (format: win64/elf64/macho64/macho32/elf32)

## Incremental Builds

Three levels of incrementality:

1. **mtime** — if output is newer than all inputs, skip
2. **`.d` files** — header change tracking (including transitive)
3. **SHA256 fingerprint** — recompile if compiler flags changed (stored in `.dcr_fingerprint`)

## Parallel Compilation

- `thread::scope` for thread pool
- Atomic task queue (`AtomicU64`)
- Mutex on stdout (`OUTPUT_MUTEX`)
- Thread count = `available_parallelism()`

## Build Kinds

| Kind | Type | Path (Linux example) |
|------|------|---------------------|
| `bin` | Executable | `target/<triple>/<profile>/<name>` (.exe on Windows) |
| `staticlib` | Static library | `target/<triple>/<profile>/lib<name>.a` (.lib) |
| `sharedlib` | Dynamic library | `target/<triple>/<profile>/lib<name>.so` (.dll/.dylib) |
| `efi` | UEFI application | `target/<triple>/<profile>/<name>.efi` |
| `elf` | ELF without stdlib | `target/<triple>/<profile>/<name>` |
| `none` | Compile only, no link | — |
| `custom` | Full filename+extension control | `target/<triple>/<profile>/<filename>.<extension>` |

## Build Steps

DCR supports pre-build and post-build steps:

- `build.steps` — commands before compilation
- `build.post_steps` — commands after compilation

Substitutions: `{stem}`, `{in}`, `{out}`, `{profile}`, `{version}`, `{name}`.

Example Qt codegen via build steps:

```toml
[build.steps]
moc = "moc {in} -o {out}"
```

## pkg-config

Automatic lookup (read from raw config):

```toml
[build]
pkg_config = ["sdl2", "gl"]
```

DCR runs `pkg-config --cflags sdl2 gl` and `pkg-config --libs sdl2 gl` and adds results to compiler/linker flags.

## Variable Substitution

Supported variables:

| Variable | Description |
|----------|-------------|
| `{version}` | Package version |
| `{version_major}` | Major version part |
| `{version_minor}` | Minor version part |
| `{version_patch}` | Patch version |
| `{version_suffix}` | Suffix (e.g., `-rc1`) |
| `{version_suffix_dash}` | Suffix with dash |
| `{profile}` | Profile name (debug/release) |
| `{name}` | Package name |