reduce

Active contributors: andrewrk

Purpose

lib/compiler/reduce.zig (~17 KB) is a Zig source minimizer. It backs zig reduce. Given an input .zig file plus an interestingness script (a program that exits 0 when the file still reproduces the bug), it shrinks the source while preserving the property — the same idea as creduce/cvise for C, but for Zig.

How to use it

zig reduce --interesting ./check.sh -- input.zig
# After many iterations, input.zig is rewritten to a smaller form
# that still satisfies ./check.sh.

The "interestingness" script is anything that returns 0 to mean "still reproduces the bug" and non-zero otherwise. A typical script invokes zig with the failure-causing flags and greps the output for the bug signature.

Implementation sketch

The reducer walks the AST (via lib/std/zig/Ast.zig) and applies a battery of transformations:

• Removing top-level declarations.
• Replacing function bodies with unreachable or trivial returns.
• Removing block statements, if branches, loops.
• Inlining single-use bindings.
• Replacing complex literals with simpler ones.

After each transformation candidate, it re-runs the interestingness script. Successful shrinks are kept; unsuccessful ones are reverted.

Integration points

• std.zig.Ast — the AST it edits.
• std.zig.Parse — re-parsing after each transformation.
• std.Process — running the interestingness script.

Key source files

File	Purpose
lib/compiler/reduce.zig	The reducer.
lib/std/zig/Ast.zig	AST reader/writer used for transformations.

See Debugging for when to reach for zig reduce.