Zig Compiler

Purpose

Guide agents through Zig compiler invocation: optimization modes, output types, zig cc as a C compiler drop-in, error message interpretation, and the Zig compilation pipeline.

Triggers

• "How do I compile a Zig program?"
• "What are Zig's optimization modes and when do I use each?"
• "How do I use zig cc to compile C code?"
• "How do I read Zig error messages?"
• "How do I compile a Zig library?"
• "What is zig ast-check?"

Workflow

1. Basic compilation

# Compile and run a single file
zig run src/main.zig

# Compile to executable
zig build-exe src/main.zig

# Compile to static library
zig build-lib src/mylib.zig

# Compile to shared library
zig build-lib src/mylib.zig -dynamic

# Compile to object file
zig build-obj src/main.zig

# Output name
zig build-exe src/main.zig -femit-bin=myapp

2. Optimization modes

Mode	Flag	-O equiv	Purpose
Debug (default)	-O Debug	-O0 -g	Fast compile, all safety checks, debug info
ReleaseSafe	-O ReleaseSafe	-O2 + checks	Optimized with safety checks retained
ReleaseFast	-O ReleaseFast	-O3	Maximum speed, safety checks removed
ReleaseSmall	-O ReleaseSmall	-Os	Minimize binary size

zig build-exe src/main.zig -O Debug        # dev builds
zig build-exe src/main.zig -O ReleaseSafe  # production with safety
zig build-exe src/main.zig -O ReleaseFast  # max performance
zig build-exe src/main.zig -O ReleaseSmall # embedded/WASM

Safety checks in Debug and ReleaseSafe:

• Integer overflow → detected and panics with source location
• Array bounds checking → panics on OOB
• Null pointer dereference → panic (not crash)
• unreachable → panic
• Enum tag validation → panic on bad cast

ReleaseFast: turns safety checks into undefined behaviour (same semantics as C -O3). Use only when you've validated with ReleaseSafe first.

3. Target specification

# List all supported targets
zig targets

# Cross-compile for specific target
zig build-exe src/main.zig \
    -target aarch64-linux-gnu \
    -O ReleaseFast

# Embedded (no OS)
zig build-exe src/main.zig \
    -target thumb-freestanding-eabi \
    -O ReleaseSmall

# WebAssembly
zig build-exe src/main.zig \
    -target wasm32-freestanding \
    -O ReleaseSmall \
    --export=main

# Common target triples: cpu-os-abi
# x86_64-linux-gnu, x86_64-windows-gnu, aarch64-macos-none
# thumbv7m-freestanding-eabi, wasm32-wasi, wasm32-freestanding

4. zig cc — C compiler drop-in

Zig ships a C/C++ compiler (zig cc / zig c++) backed by Clang and musl. It is hermetic — no system libc required.

# Compile C code
zig cc -O2 -Wall main.c -o myapp

# Compile C++ code
zig c++ -std=c++17 -O2 main.cpp -o myapp

# Cross-compile C for ARM (no cross toolchain needed!)
zig cc -target aarch64-linux-gnu -O2 main.c -o myapp-arm

# Statically link with musl
zig cc -target x86_64-linux-musl main.c -o myapp-static

# Use in CMake (override compiler)
CC="zig cc" CXX="zig c++" cmake -S . -B build
cmake --build build

# Use in Makefile
CC="zig cc" make

zig cc advantages over gcc/clang:

• No system toolchain required (fully hermetic)
• Built-in cross-compilation for any supported target
• Always ships with a recent clang version
• musl libc bundled for static Linux builds

5. Emit formats

# Emit LLVM IR
zig build-exe src/main.zig --emit-llvm-ir

# Emit assembly
zig build-exe src/main.zig --emit-asm
cat main.s

# Emit binary and assembly
zig build-exe src/main.zig -femit-bin=myapp -femit-asm=myapp.s

6. AST check and syntax validation

# Check syntax without compiling
zig ast-check src/main.zig

# Format code
zig fmt src/main.zig
zig fmt src/          # format entire directory

# Check formatting without modifying
zig fmt --check src/

# Tokenize (debugging zig fmt)
zig tokenize src/main.zig

7. Reading Zig error messages

Zig error messages include:

• Source file and line
• Column indicator with arrow
• Note messages for context

src/main.zig:10:5: error: expected type 'u32', found 'i32'
    x: i32 = 5,
    ^
src/main.zig:7:5: note: struct field 'x' declared here
    x: u32,
    ^

Key error patterns:

Error	Meaning
error: expected type 'X', found 'Y'	Type mismatch
error: use of undeclared identifier 'X'	Missing import or typo
error: integer overflow	Comptime overflow (caught at compile)
error: cannot assign to constant	Mutating a const variable
error: unused variable 'x'	All variables must be used
error: unused function parameter 'x'	Use _ = x; to suppress

Suppress "unused" errors:

_ = unused_variable;  // explicitly discard

8. Version and environment

# Check Zig version
zig version

# Show build configuration
zig env

# Show standard library location
zig env | grep lib_dir

For optimization mode details and target triple reference, see references/zig-optimize-modes.md.

Related skills

• Use skills/zig/zig-build-system for multi-file projects with build.zig
• Use skills/zig/zig-cinterop for calling C from Zig and vice versa
• Use skills/zig/zig-cross for cross-compilation targets and sysroots
• Use skills/zig/zig-debugging for GDB/LLDB with Zig binaries