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Patch installers

A patch installer carries only what changed between two versions: binary deltas for modified files (or full bytes where a delta would be larger), plus the list of files to delete. Unchanged files have no payload entry at all, so a patch is typically a fraction of the size of a full installer.

You enter patch mode by passing both --from-version and --from-dir:

.\target\release\installer_builder.exe pack `
    --product      "My App" `
    --product-id   myapp `
    --publisher    "My Company" `
    --from-version 1.0 --from-dir .\build\myapp-1.0 `
    --to-version   1.1 --input    .\build\myapp-1.1 `
    --exe          myapp.exe `
    --priv-key     .\keys\priv.key `
    --pub-key      .\keys\pub.key `
    --out          .\dist\patch-myapp-1.0-to-1.1.exe

--from-version and --from-dir are required together. Passing only one is an error. Everything else works exactly as for a full installer, including the config file and toolchain-free mode.

How the payload is chosen, per file

For each file in the new version:

CaseWhat ships
New file (absent from the old directory)The full file.
Unchanged (same BLAKE3 hash as the old file)Nothing. The installer keeps the file already on disk.
ChangedThe builder runs hdiffz to produce a delta. If the delta is smaller than the full file, the delta ships; otherwise the full file does.

Files present only in the old version are recorded in deleted_files and removed at install time.

hdiffz.exe is required for real deltas

Delta generation calls hdiffz.exe, which must sit next to installer_builder.exe. If it is missing, the builder prints:

warning: ...\hdiffz.exe not found - patch payload will ship full files instead of HDiffPatch deltas

The patch installer still works; it just is not smaller than a full one.

Version pinning

A patch installer records its from_version and refuses to run unless the target install's version.json matches. This refusal happens before anything is touched: the existing install keeps working, and in silent mode the process exits with code 10 so a launcher can fall back to the full installer. See Exit codes.

Dev option: force a reinstall from scratch

--force-reinstall (valid on full and patch builds) produces an installer that skips the from-version check, rewrites every file without hash-skipping, and removes orphan files, so the install matches the build exactly. It stays fully transactional. Use it during development; ship normal installers to users.