---
sidebar_label: Build system
---

# Build System

## Compiler Backends

DCR supports 7 compilation backends. Selection is automatic based on file extension and `build.compiler` value.

| 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`, `.s`                      | x86/x86_64 NASM assembler             |
| `masm`    | `.asm`                            | MASM (ml/ml64) on Windows             |
| `fasm`    | `.asm`, `.fasm`                   | Flat Assembler                        |
| `llvm_ir` | `.ll`                             | LLVM IR via `llc -filetype=obj`       |

## Qt Support

DCR provides native Qt support for automatic meta-object handling (MOC, UIC, RCC).

Enable it by setting `build.qt = true` in `dcr.toml`. DCR will automatically detect Qt-related files (`.ui`, `.qrc`, `.h` with `Q_OBJECT`) and process them.

```toml
[build]
qt = true
```

*Note: Requires `qt6` modules (Core, Widgets, Gui, Svg) installed via `pkg-config`.*

Advanced customization is still possible via `build.steps` if special handling is needed:

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

### 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 / MASM / FASM / LLVM-IR

* GAS: `-I`, `-c -o`, `--defsym`
* NASM: `-I`, `-o`, `-D`, `-f` (format: win64/elf64/macho64/macho32/elf32; **`bin` when `kind = "flat-bin"`**)
* MASM: `/nologo /c /Fo\<obj> <source>`
* FASM: `<source> \<output>` (output path is the object file)
* LLVM IR: `-filetype=obj <source> -o \<output>`

## 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()`, capped by `build.codegen-units` if set

## 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>`                    |
| `flat-bin`  | Raw binary                      | ASM: `\<stem>.bin` (NASM `-f bin` / FASM / GAS·MASM·LLC via objcopy); C/C++: `\<name>.bin` (link + objcopy) |

## Disk images (`[archive]`)

After a successful build, if `[archive]` is present in `dcr.toml`, DCR formats a FAT volume and copies files from `layout` into the image. See [dcr.toml → archive](/docs/reference/dcr-toml#archive).

## 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                 |