This document gives a high-level overview of chezmoi’s source code for anyone interested in contributing to chezmoi.
You can generate Go documentation for chezmoi’s source code with
go doc, for
$ go doc -all -u github.com/twpayne/chezmoi/v2/internal/chezmoi
You can also browse chezmoi’s generated documentation online but this only includes exported symbols.
Directory structure #
The important directories in chezmoi are:
||The documentation single source of truth. Help text, examples, and the chezmoi.io website are generated from the files in this directory, particularly
||chezmoi’s core functionality|
||Code for the
||High-level tests of chezmoi’s commands using
Key concepts #
As described in the reference manual, chezmoi evaluates the source state to compute a target state for the destination directory (typically your home directory). It then compares the target state to the actual state of the destination directory and performs any changes necessary to update the destination directory to match the target state. The concepts are represented directly in chezmoi’s code.
chezmoi uses the generic term entry to describe something that it manages. Entries can be files, directories, symlinks, scripts, amongst other things.
All of chezmoi’s interaction with the operating system is abstracted through the
System interface. A
System includes functionality to read and write files
and directories and execute commands. chezmoi makes a distinction between
idempotent commands that can be run multiple times without modifying the
underlying system and arbitrary commands that may modify the underlying system.
The real underlying system is implemented via a
RealSystem struct. Other
Systems are composed on top of this to provide further functionality. For
--debug flag is implemented by wrapping the
RealSystem with a
DebugSystem that logs all calls to the underlying
implemented by wrapping the
RealSystem with a
DryRunSystem that allows reads
to pass through but silently discards all writes.
SourceState struct represents a source state, including reading a source
state from the source directory, executing templates, applying the source state
(i.e. updating a
System to match the desired source state), and adding more
entries to the source state.
Entries in the source state are abstracted by the
implemented by the
SourceStateDir structs, as the source
state only consists of regular files and directories.
SourceStateFile includes a
FileAttr struct describing the attributes
parsed from its file name. Similarly, a
SourceStateDir includes a
struct describing the directory attributes parsed from a directory name.
SourceStateEntrys can compute their target state entries, i.e. what the
equivalent entry should be in the target state, abstracted by the
Actual target state entries include
TargetStateFile structs, representing a
file with contents and permissions,
TargetStateDir structs, representing a
TargetStateSymlink for symlinks,
TargetStateRemove for entries
that should be removed, and
TargetStateScript for scripts that should be run.
The actual state of an entry in the target state is abstracted via the
ActualStateEntry interface, with
ActualStateSymlink structs implementing this interface.
EntryState struct represents a serialization of an
ActualEntryState for storage in and retrieval from chezmoi’s persistent state.
It stores a SHA256 of the entry’s contents, rather than the full contents, to
avoid storing secrets in the persistent state.
With these concepts, chezmoi’s apply command is effectively:
- Read the source state from the source directory.
- For each entry in the source state (
SourceStateEntry), compute its
TargetStateEntryand read its actual state in the destination state (
- If the
ActualStateEntryis not equivalent to the
TargetStateEntrythen apply the minimal set of changes to the
ActualStateEntryso that they are equivalent.
Furthermore, chezmoi stores the
EntryState of each entry that it writes in its
persistent state. chezmoi can then detect if a third party has updated a target
since chezmoi last wrote it by comparing the actual state entry in the target
state with the entry state in the persistent state.
internal/cmd/*cmd.go contains the code for each individual command and
internal/cmd/*templatefuncs.go contain the template functions.
Commands are defined as methods on the
Config struct. The
Config struct is
large, containing all configuration values read from the config file, command
line arguments, and computed and cached values.
set up and tear down state for individual commands based on the command’s
Path handling #
chezmoi uses separate types for absolute paths (
AbsPath) and relative paths
RelPath) to avoid errors where paths are combined (e.g. joining two absolute
paths). A further type
SourceRelPath is a relative path within the source
directory and handles file and directory attributes.
Internally, chezmoi normalizes all paths to use forward slashes with an optional
upper-cased Windows volume so they can be compared with string comparisons.
Paths read from the user may include tilde (
~) to represent the user’s home
directory, use forward or backward slashes, and are treated as external paths
ExtPath). These are normalized to absolute paths. chezmoi is case-sensitive
internally and makes no attempt to handle case-insensitive or case-preserving
Persistent state #
Persistent state is treated as a two-level key-value store with the
PersistentState interface defines interaction with
them. Sometimes temporary persistent states are used. For example, in dry run
--dry-run) the actual persistent state is copied into a temporary
persistent state in memory which remembers writes but does not persist them to
Encryption tools are abstracted by the
Encryption interface that contains
methods of encrypting and decrypting files and
bytes. Implementations are
GPGEncryption structs. A
Encryption interface and logs the methods called.
The execution of a
run_once_ script is recorded by storing the SHA256 of its
contents in the
scriptState bucket in the persistent state. On future
invocations the script is only run if no matching contents SHA256 is found in
the persistent state.
The execution of a
run_onchange_ script is recorded by storing its target name
entryState bucket along with its contents SHA256 sum. On future
invocations the script is only run if its contents SHA256 sum has changed, and
its contents SHA256 sum is then updated in the persistent state.
chezmoi has a mix of, unit, integration, and end-to-end tests. Unit and
integration tests use the
framework. End-to-end tests use
with the test scripts themselves in
testdata/scripts. You can run individual
end-to-end tests with
$ go test ./internal/cmd -run=TestScript/<name>
<name> is the basename of file in
Tests should, if at all possible, run unmodified on all operating systems tested in CI (Linux, macOS, Windows, and FreeBSD). Windows will sometimes need special handling due to its path separator and lack of POSIX-style file permissions.