* Add args in .nurc file to environment
* Working dummy version
* Add add_nurc to sync_env command
* Parse .nurc file
* Delete env vars after leaving directory
* Removing vals not working, strangely
* Refactoring, add comment
* Debugging
* Debug by logging to file
* Add and remove env var behavior appears correct
However, it does not use existing code that well.
* Move work to cli.rs
* Parse config directories
* I am in a state of distress
* Rename .nurc to .nu
* Some notes for me
* Refactoring
* Removing vars works, but not done in a very nice fashion
* Refactor env_vars_to_delete
* Refactor env_vars_to_add()
* Move directory environment code to separate file
* Refactor from_config
* Restore env values
* Working?
* Working?
* Update comments and change var name
* Formatting
* Remove vars after leaving dir
* Remove notes I made
* Rename config function
* Clippy
* Cleanup and handle errors
* cargo fmt
* Better error messages, remove last (?) unwrap
* FORMAT PLZ
* Rename whitelisted_directories to allowed_directories
* Add comment to clarify how overwritten values are restored.
* Change list of allowed dirs to indexmap
* Rewrite starting
* rewrite everything
* Overwritten env values tracks an indexmap instead of vector
* Refactor restore function
* Untrack removed vars properly
* Performance concerns
* Performance concerns
* Error handling
* Clippy
* Add type aliases for String and OsString
* Deletion almost works
* Working?
* Error handling and refactoring
* nicer errors
* Add TODO file
* Move outside of loop
* Error handling
* Reworking adding of vars
* Reworking adding of vars
* Ready for testing
* Refactoring
* Restore overwritten vals code
* todo.org
* Remove overwritten values tracking, as it is not needed
* Cleanup, stop tracking overwritten values as nu takes care of it
* Init autoenv command
* Initialize autoenv and autoenv trust
* autoenv trust toml
* toml
* Use serde for autoenv
* Optional directory arg
* Add autoenv untrust command
* ... actually add autoenv untrust this time
* OsString and paths
* Revert "OsString and paths"
This reverts commit e6eedf8824.
* Fix path
* Fix path
* Autoenv trust and untrust
* Start using autoenv
* Check hashes
* Use trust functionality when setting vars
* Remove unused code
* Clippy
* Nicer errors for autoenv commands
* Non-working errors
* Update error description
* Satisfy fmt
* Errors
* Errors print, but not nicely
* Nicer errors
* fmt
* Delete accidentally added todo.org file
* Rename direnv to autoenv
* Use ShellError instead of Error
* Change tests to pass, danger zone?
* Clippy and errors
* Clippy... again
* Replace match with or_else
* Use sha2 crate for hashing
* parsing and error msg
* Refactoring
* Only apply vars once
* if parent dir
* Delete vars
* Rework exit code
* Adding works
* restore
* Fix possibility of infinite loop
* Refactoring
* Non-working
* Revert "Non-working"
This reverts commit e231b85570.
* Revert "Revert "Non-working""
This reverts commit 804092e46a.
* Autoenv trust works without restart
* Cargo fix
* Script vars
* Serde
* Serde errors
* Entry and exitscripts
* Clippy
* Support windows and handle errors
* Formatting
* Fix infinite loop on windows
* Debugging windows loop
* More windows infinite loop debugging
* Windows loop debugging #3
* windows loop #4
* Don't return err
* Cleanup unused code
* Infinite loop debug
* Loop debugging
* Check if infinite loop is vars_to_add
* env_vars_to_add does not terminate, skip loop as test
* Hypothesis: std::env::current_dir() is messing with something
* Hypothesis: std::env::current_dir() is messing with something
* plz
* make clippy happy
* debugging in env_vars_to_add
* Debbuging env_vars_to_add #2
* clippy
* clippy..
* Fool clippy
* Fix another infinite loop
* Binary search for error location x)
* Binary search #3
* fmt
* Binary search #4
* more searching...
* closing in... maybe
* PLZ
* Cleanup
* Restore commented out functionality
* Handle case when user gives the directory "."
* fmt
* Use fs::canonicalize for paths
* Create optional script section
* fmt
* Add exitscripts even if no entryscripts are defined
* All sections in .nu-env are now optional
* Re-read config file each directory change
* Hot reload after autoenv untrust, don't run exitscripts if untrusted
* Debugging
* Fix issue with recursive adding of vars
* Thank you for finding my issues Mr. Azure
* use std::env
* Update calculate to return a table when Value is a table
* impl mode subcommand for math
* add tests for math mode subcommand
* add table/row tests for math mode subcommand
* fix formatting
* WIP - changes to support bat config
* added bat configuration
* removed debug info
* clippy fix
* changed [bat] to [textview]
Co-authored-by: Darren Schroeder <fdncred@hotmail.com>
* WIP - Modified textview to use bat crate
* use input_from_bytes_with_name instead of input_file
* removed old paging
added prettyprint on else blocks
duplicated too much code
hard coded defaults
Co-authored-by: Darren Schroeder <fdncred@hotmail.com>
* WIP - not compiling
* compiling but panicing
* still broken
* nearly working
* reverted deserializer_string changes
updated enter.rs and open.rs to use Option<Tagged<String>>
Accepted Clippy suggestions
Accepted fmt suggestions
Left original code from open.rs
We may want to use some of it and only fallback to encoding.
* Don't exit when there is an unknown encoding.
* When encoding is unknown default to utf-8.
* only do encoding if the user says to it
* merged some conflicts on open
* made error messages consistent
* Updated unwrap with expect
* updated open test to pass with more descriptive err
updated enter test to not fail
* change _location to location
* changed _visitor to visitor
* Added a more verbose usage statement for encoding
Linked to docs.rs/encoding_rs for details
Co-authored-by: Darren Schroeder <fdncred@hotmail.com>
* Possible implementation of globbing for start command
* Whoops forgot to remove Error used for debugging
* Use string lossy
* Run clippy
* Pin glob
* Better error messages
* Remove unneeded comment
* added helper to convert data to strings
added ability to auto-rotate single row output
if row will be greater than terminal width
* Added pivot_to_fit config value
* Added ColumnPath to convert_to_string helper
* Figured out I had to run `cargo fmt --all -- --check`
Co-authored-by: Darren Schroeder <fdncred@hotmail.com>
* mvp for start command
* modified the signature of the start command
* parse filenames
* working model for macos is done
* refactored to read from pipes
* start command works well on macos; manual testing reveals need of --args flag support
* implemented start error; color printing of warning and errors
* ran clippy and fixed warnings
* fix a clippy lint that was caught in pipeline
* fix dead code clippy lint for windows
* add cfg annotation to import
* Changes to allow plugins to be loaded in a multi-threaded manner in order to decrease startup time.
* Ran rust fmt and clippy to find and fix first pass errors.
Updated launch.jason to make debugging easier in vscode.
Also added tasks.json so tasks like clippy can be ran easily.
* ran fmt again
* Delete launch.json
Remove IDE settings file
* Remove IDE settings file
* Ignore vscode IDE settings
* Cloned the context instead of Arc/Mutexing it.
Co-authored-by: Darren Schroeder <fdncred@hotmail.com>
Co-authored-by: Jonathan Turner <jonathandturner@users.noreply.github.com>
* fix: absolutize path against its parent if it was a symlink.
On Linux this happens because Rust calls readlink but doesn't canonicalize the resultant path.
* feat: playground function to create symlinks
* fix: use playground dirs
* feat: test for #1631, shift tests names
* Creation of FilesystemShell with custom location may fail
* Replace ichwh with which
* Creation of FilesystemShell with custom location may fail
* Replace ichwh with which
* fix: add ichwh again since it cannot be completely replaced
* fix: replace one more use of which
* Making Commands match what UntaggedValue needs
* WIP
* WIP
* WIP
* Moved to expressions for conditions
* Add 'each' command to use command blocks
* More cleanup
* Add test for 'each'
* Instead use an expression block
Previously, if the user didn't have the appropriate permissions to execute the
binary/script, they would see "command not found", which is confusing.
This commit eliminates the `which` crate in favour of `ichwh`, which deals
better with permissions by not dealing with them at all! This is closer to the
behaviour of `which` in many shells. Permission checks are then left up to the
caller to deal with.
* WIP: move to bytes codec
* Progress on adding collect helpers
* Progress on adding collect helpers
* Add in line splitting back to lines
* Lines outputting line primitives
* Close to ready?
* Finish fixing lines
* clippy fixes
* fmt fixes
* removed unused code
* Cleanup a few bits
* Cleanup a few bits
* Cleanup a few more bits
* Fix failing test with corrected test case
This improves incremental build time when working on what was previously
the root package. For example, previously all plugins would be rebuilt
with a change to `src/commands/classified/external.rs`, but now only
`nu-cli` will have to be rebuilt (and anything that depends on it).
* Add block size to du
* Change blocks to physical size
* Use path instead of strings for file/directory names
* Why don't I just use paths instead of strings anyway?
* shorten physical size and apparent size to physical and apparent resp.
* Refactor pipeline ahead of block changes. Add '-c' commandline option
* Update pipelining an error value
* Fmt
* Clippy
* Add stdin redirect for -c flag
* Add stdin redirect for -c flag
* Upgrade futures, async-stream, and futures_codec
These were the last three dependencies on futures-preview. `nu` itself
is now fully dependent on `futures@0.3`, as opposed to `futures-preview`
alpha.
Because the update to `futures` from `0.3.0-alpha.19` to `0.3.0` removed
the `Stream` implementation of `VecDeque` ([changelog][changelog]), most
commands that convert a `VecDeque` to an `OutputStream` broke and had to
be fixed.
The current solution is to now convert `VecDeque`s to a `Stream` via
`futures::stream::iter`. However, it may be useful for `futures` to
create an `IntoStream` trait, implemented on the `std::collections` (or
really any `IntoIterator`). If something like this happends, it may be
worthwhile to update the trait implementations on `OutputStream` and
refactor these commands again.
While upgrading `futures_codec`, we remove a custom implementation of
`LinesCodec`, as one has been added to the library. There's also a small
refactor to make the stream output more idiomatic.
[changelog]: https://github.com/rust-lang/futures-rs/blob/master/CHANGELOG.md#030---2019-11-5
* Upgrade sys & ps plugin dependencies
They were previously dependent on `futures-preview`, and `nu_plugin_ps`
was dependent on an old version of `futures-timer`.
* Remove dependency on futures-timer from nu
* Update Cargo.lock
* Fix formatting
* Revert fmt regressions
CI is still on 1.40.0, but the latest rustfmt v1.41.0 has changes to the
`val @ pattern` syntax, causing the linting job to fail.
* Fix clippy warnings
Restructure and streamline token expansion
The purpose of this commit is to streamline the token expansion code, by
removing aspects of the code that are no longer relevant, removing
pointless duplication, and eliminating the need to pass the same
arguments to `expand_syntax`.
The first big-picture change in this commit is that instead of a handful
of `expand_` functions, which take a TokensIterator and ExpandContext, a
smaller number of methods on the `TokensIterator` do the same job.
The second big-picture change in this commit is fully eliminating the
coloring traits, making coloring a responsibility of the base expansion
implementations. This also means that the coloring tracer is merged into
the expansion tracer, so you can follow a single expansion and see how
the expansion process produced colored tokens.
One side effect of this change is that the expander itself is marginally
more error-correcting. The error correction works by switching from
structured expansion to `BackoffColoringMode` when an unexpected token
is found, which guarantees that all spans of the source are colored, but
may not be the most optimal error recovery strategy.
That said, because `BackoffColoringMode` only extends as far as a
closing delimiter (`)`, `]`, `}`) or pipe (`|`), it does result in
fairly granular correction strategy.
The current code still produces an `Err` (plus a complete list of
colored shapes) from the parsing process if any errors are encountered,
but this could easily be addressed now that the underlying expansion is
error-correcting.
This commit also colors any spans that are syntax errors in red, and
causes the parser to include some additional information about what
tokens were expected at any given point where an error was encountered,
so that completions and hinting could be more robust in the future.
Co-authored-by: Jonathan Turner <jonathandturner@users.noreply.github.com>
Co-authored-by: Andrés N. Robalino <andres@androbtech.com>
This commit changes the way we shell out externals when using the `"$it"` argument. Also pipes per row to an external's stdin if no `"$it"` argument is present for external commands.
Further separation of logic (preparing the external's command arguments, getting the data for piping, emitting values, spawning processes) will give us a better idea for lower level details regarding external commands until we can find the right abstractions for making them more generic and unify within the pipeline calling logic of Nu internal's and external's.
* Detect built-in commands passed as args to `which`
This expands the built-in `which` command to detect nushell commands
that may have the same name as a binary in the path.
* Allow which to interpret multiple arguments
Previously, it would discard any argument besides the first. This allows
`which` to process multiple arguments. It also makes the output a stream
of rows.
* Use map to build the output
* Add boolean column for builtins
* Use macros for entry creation shortcuts
* Process command args and use async_stream
In order to use `ichwh`, I'll need to use async_stream. But in order to
avoid lifetime errors with that, I have to process the command args
before using them. I'll admit I don't fully understand what is going on
with the `args.process(...)` function, but it works.
* Use `ichwh` for path searching
This commit transitions from `which` to `ichwh`. The path search is now
done asynchronously.
* Enable the `--all` flag on `which`
* Make `which` respect external commands
Escaped commands passed to wich (e.g., `which "^ls"`), are now searched
before builtins.
* Fix clippy warnings
This commit resolves two warnings from clippy, in light of #1142.
* Update Cargo.lock to get new `ichwh` version
`ichwh@0.2.1` has support for local paths.
* Add documentation for command
* Manifests check. Ignore doctests for now.
* We continue with refactorings towards the separation of concerns between
crates. `nu_plugin_inc` and `nu_plugin_str` common test helpers usage
has been refactored into `nu-plugin` value test helpers.
Inc also uses the new API for integration tests.
This commit contains two improvements:
- Support for a Range syntax (and a corresponding Range value)
- Work towards a signature syntax
Implementing the Range syntax resulted in cleaning up how operators in
the core syntax works. There are now two kinds of infix operators
- tight operators (`.` and `..`)
- loose operators
Tight operators may not be interspersed (`$it.left..$it.right` is a
syntax error). Loose operators require whitespace on both sides of the
operator, and can be arbitrarily interspersed. Precedence is left to
right in the core syntax.
Note that delimited syntax (like `( ... )` or `[ ... ]`) is a single
token node in the core syntax. A single token node can be parsed from
beginning to end in a context-free manner.
The rule for `.` is `<token node>.<member>`. The rule for `..` is
`<token node>..<token node>`.
Loose operators all have the same syntactic rule: `<token
node><space><loose op><space><token node>`.
The second aspect of this pull request is the beginning of support for a
signature syntax. Before implementing signatures, a necessary
prerequisite is for the core syntax to support multi-line programs.
That work establishes a few things:
- `;` and newlines are handled in the core grammar, and both count as
"separators"
- line comments begin with `#` and continue until the end of the line
In this commit, multi-token productions in the core grammar can use
separators interchangably with spaces. However, I think we will
ultimately want a different rule preventing separators from occurring
before an infix operator, so that the end of a line is always
unambiguous. This would avoid gratuitous differences between modules and
repl usage.
We already effectively have this rule, because otherwise `x<newline> |
y` would be a single pipeline, but of course that wouldn't work.
Previously, external words accidentally used
ExpansionRule::new().allow_external_command(), when it should have been
ExpansionRule::new().allow_external_word().
External words are the broadest category in the parser, and are the
appropriate category for external arguments. This was just a mistake.
This was achieved by deleting Cargo.lock
and letting a recent Cargo nightly re-create
it. Support for the format was already
introduced in Rust 1.38, but currently,
stable releases of Cargo only retain it
if encountered but don't generate such
files by default.
The new format is smaller, better suited to
prevent merge conflicts and generates smaller
diffs at dependency updates, leading to
smaller git history.
You can read more about it in this PR: https://github.com/rust-lang/cargo/pull/7070
This commit extracts five new crates:
- nu-source, which contains the core source-code handling logic in Nu,
including Text, Span, and also the pretty.rs-based debug logic
- nu-parser, which is the parser and expander logic
- nu-protocol, which is the bulk of the types and basic conveniences
used by plugins
- nu-errors, which contains ShellError, ParseError and error handling
conveniences
- nu-textview, which is the textview plugin extracted into a crate
One of the major consequences of this refactor is that it's no longer
possible to `impl X for Spanned<Y>` outside of the `nu-source` crate, so
a lot of types became more concrete (Value became a concrete type
instead of Spanned<Value>, for example).
This also turned a number of inherent methods in the main nu crate into
plain functions (impl Value {} became a bunch of functions in the
`value` namespace in `crate::data::value`).
This commit extracts Tag, Span, Text, as well as source-related debug
facilities into a new crate called nu_source.
This change is much bigger than one might have expected because the
previous code relied heavily on implementing inherent methods on
`Tagged<T>` and `Spanned<T>`, which is no longer possible.
As a result, this change creates more concrete types instead of using
`Tagged<T>`. One notable example: Tagged<Value> became Value, and Value
became UntaggedValue.
This change clarifies the intent of the code in many places, but it does
make it a big change.
The original purpose of this PR was to modernize the external parser to
use the new Shape system.
This commit does include some of that change, but a more important
aspect of this change is an improvement to the expansion trace.
Previous commit 6a7c00ea adding trace infrastructure to the syntax coloring
feature. This commit adds tracing to the expander.
The bulk of that work, in addition to the tree builder logic, was an
overhaul of the formatter traits to make them more general purpose, and
more structured.
Some highlights:
- `ToDebug` was split into two traits (`ToDebug` and `DebugFormat`)
because implementations needed to become objects, but a convenience
method on `ToDebug` didn't qualify
- `DebugFormat`'s `fmt_debug` method now takes a `DebugFormatter` rather
than a standard formatter, and `DebugFormatter` has a new (but still
limited) facility for structured formatting.
- Implementations of `ExpandSyntax` need to produce output that
implements `DebugFormat`.
Unlike the highlighter changes, these changes are fairly focused in the
trace output, so these changes aren't behind a flag.
* Moves off of draining between filters. Instead, the sink will pull on the stream, and will drain element-wise. This moves the whole stream to being lazy.
* Adds ctrl-c support and connects it into some of the key points where we pull on the stream. If a ctrl-c is detect, we immediately halt pulling on the stream and return to the prompt.
* Moves away from having a SourceMap where anchor locations are stored. Now AnchorLocation is kept directly in the Tag.
* To make this possible, split tag and span. Span is largely used in the parser and is copyable. Tag is now no longer copyable.
This commit adds the ability to work on features behind a feature flag
that won't be included in normal builds of nu.
These features are not exposed as Cargo features, as they reflect
incomplete features that are not yet stable.
To create a feature, add it to `features.toml`:
```toml
[hintsv1]
description = "Adding hints based on error states in the highlighter"
enabled = false
```
Each feature in `features.toml` becomes a feature flag accessible to `cfg`:
```rs
println!("hintsv1 is enabled");
```
By default, features are enabled based on the value of the `enabled` field.
You can also enable a feature from the command line via the
`NUSHELL_ENABLE_FLAGS` environment variable:
```sh
$ NUSHELL_ENABLE_FLAGS=hintsv1 cargo run
```
You can enable all flags via `NUSHELL_ENABLE_ALL_FLAGS`.
This commit also updates the CI setup to run the build with all flags off and
with all flags on. It also extracts the linting test into its own
parallelizable test, which means it doesn't need to run together with every
other test anymore.
When working on a feature, you should also add tests behind the same flag. A
commit is mergable if all tests pass with and without the flag, allowing
incomplete commits to land on master as long as the incomplete code builds and
passes tests.
The main thrust of this (very large) commit is an overhaul of the
expansion system.
The parsing pipeline is:
- Lightly parse the source file for atoms, basic delimiters and pipeline
structure into a token tree
- Expand the token tree into a HIR (high-level intermediate
representation) based upon the baseline syntax rules for expressions
and the syntactic shape of commands.
Somewhat non-traditionally, nu doesn't have an AST at all. It goes
directly from the token tree, which doesn't represent many important
distinctions (like the difference between `hello` and `5KB`) directly
into a high-level representation that doesn't have a direct
correspondence to the source code.
At a high level, nu commands work like macros, in the sense that the
syntactic shape of the invocation of a command depends on the
definition of a command.
However, commands do not have the ability to perform unrestricted
expansions of the token tree. Instead, they describe their arguments in
terms of syntactic shapes, and the expander expands the token tree into
HIR based upon that definition.
For example, the `where` command says that it takes a block as its first
required argument, and the description of the block syntactic shape
expands the syntax `cpu > 10` into HIR that represents
`{ $it.cpu > 10 }`.
This commit overhauls that system so that the syntactic shapes are
described in terms of a few new traits (`ExpandSyntax` and
`ExpandExpression` are the primary ones) that are more composable than
the previous system.
The first big win of this new system is the addition of the `ColumnPath`
shape, which looks like `cpu."max ghz"` or `package.version`.
Previously, while a variable path could look like `$it.cpu."max ghz"`,
the tail of a variable path could not be easily reused in other
contexts. Now, that tail is its own syntactic shape, and it can be used
as part of a command's signature.
This cleans up commands like `inc`, `add` and `edit` as well as
shorthand blocks, which can now look like `| where cpu."max ghz" > 10`
Kind of touches on #356 by integrating the Starship prompt directly into the shell.
Not finished yet and has surfaced a potential bug in rustyline anyway. It depends on https://github.com/starship/starship/pull/509 being merged so the Starship prompt can be used as a library.
I could have tackled #356 completely and implemented a full custom prompt feature but I felt this was a simpler approach given that Starship is both written in Rust so shelling out isn't necessary and it already has a bunch of useful features built in.
However, I would understand if it would be preferable to just scrap integrating Starship directly and instead implement a custom prompt system which would facilitate simply shelling out to Starship.
Rids us of crossbeam v0.5 and lots of other crates.
For most users this only effects Cargo.lock though,
as rust-argon2 is only compiled when targeting
redox.
This commit migrates Value's numeric types to BigInt and BigDecimal. The
basic idea is that overflow errors aren't great in a shell environment,
and not really necessary.
The main immediate consequence is that new errors can occur when
serializing Nu values to other formats. You can see this in changes to
the various serialization formats (JSON, TOML, etc.). There's a new
`CoerceInto` trait that uses the `ToPrimitive` trait from `num_traits`
to attempt to coerce a `BigNum` or `BigDecimal` into a target type, and
produces a `RangeError` (kind of `ShellError`) if the coercion fails.
Another possible future consequence is that certain performance-critical
numeric operations might be too slow. If that happens, we can introduce
specialized numeric types to help improve the performance of those
situations, based on the real-world experience.
This commit is more substantial than it looks: there was basically no
real support for decimals before, and that impacted values all the way
through.
I also made Size contain a decimal instead of an integer (`1.6kb` is a
reasonable thing to type), which impacted a bunch of code.
The biggest impact of this commit is that it creates many more possible
ways for valid nu types to fail to serialize as toml, json, etc. which
typically can't support the full range of Decimal (or Bigint, which I
also think we should support). This commit makes to-toml fallible, and a
similar effort is necessary for the rest of the serializations.
We also need to figure out how to clearly communicate to users what has
happened, but failing to serialize to toml seems clearly superior to me
than weird errors in basic math operations.
This ended up being a bit of a yak shave. The basic idea in this commit is to
expand `~` in paths, but only in paths.
The way this is accomplished is by doing the expansion inside of the code that
parses literal syntax for `SyntaxType::Path`.
As a quick refresher: every command is entitled to expand its arguments in a
custom way. While this could in theory be used for general-purpose macros,
today the expansion facility is limited to syntactic hints.
For example, the syntax `where cpu > 0` expands under the hood to
`where { $it.cpu > 0 }`. This happens because the first argument to `where`
is defined as a `SyntaxType::Block`, and the parser coerces binary expressions
whose left-hand-side looks like a member into a block when the command is
expecting one.
This is mildly more magical than what most programming languages would do,
but we believe that it makes sense to allow commands to fine-tune the syntax
because of the domain nushell is in (command-line shells).
The syntactic expansions supported by this facility are relatively limited.
For example, we don't allow `$it` to become a bare word, simply because the
command asks for a string in the relevant position. That would quickly
become more confusing than it's worth.
This PR adds a new `SyntaxType` rule: `SyntaxType::Path`. When a command
declares a parameter as a `SyntaxType::Path`, string literals and bare
words passed as an argument to that parameter are processed using the
path expansion rules. Right now, that only means that `~` is expanded into
the home directory, but additional rules are possible in the future.
By restricting this expansion to a syntactic expansion when passed as an
argument to a command expecting a path, we avoid making `~` a generally
reserved character. This will also allow us to give good tab completion
for paths with `~` characters in them when a command is expecting a path.
In order to accomplish the above, this commit changes the parsing functions
to take a `Context` instead of just a `CommandRegistry`. From the perspective
of macro expansion, you can think of the `CommandRegistry` as a dictionary
of in-scope macros, and the `Context` as the compile-time state used in
expansion. This could gain additional functionality over time as we find
more uses for the expansion system.
