bdc32345bd
# Description We've had a lot of different issues and PRs related to arg handling with externals since the rewrite of `run-external` in #12921: - #12950 - #12955 - #13000 - #13001 - #13021 - #13027 - #13028 - #13073 Many of these are caused by the argument handling of external calls and `run-external` being very special and involving the parser handing quoted strings over to `run-external` so that it knows whether to expand tildes and globs and so on. This is really unusual and also makes it harder to use `run-external`, and also harder to understand it (and probably is part of the reason why it was rewritten in the first place). This PR moves a lot more of that work over to the parser, so that by the time `run-external` gets it, it's dealing with much more normal Nushell values. In particular: - Unquoted strings are handled as globs with no expand - The unescaped-but-quoted handling of strings was removed, and the parser constructs normal looking strings instead, removing internal quotes so that `run-external` doesn't have to do it - Bare word interpolation is now supported and expansion is done in this case - Expressions typed as `Glob` containing `Expr::StringInterpolation` now produce `Value::Glob` instead, with the quoted status from the expr passed through so we know if it was a bare word - Bare word interpolation for values typed as `glob` now possible, but not implemented - Because expansion is now triggered by `Value::Glob(_, false)` instead of looking at the expr, externals now support glob types # User-Facing Changes - Bare word interpolation works for external command options, and otherwise embedded in other strings: ```nushell ^echo --foo=(2 + 2) # prints --foo=4 ^echo -foo=$"(2 + 2)" # prints -foo=4 ^echo foo="(2 + 2)" # prints (no interpolation!) foo=(2 + 2) ^echo foo,(2 + 2),bar # prints foo,4,bar ``` - Bare word interpolation expands for external command head/args: ```nushell let name = "exa" ~/.cargo/bin/($name) # this works, and expands the tilde ^$"~/.cargo/bin/($name)" # this doesn't expand the tilde ^echo ~/($name)/* # this glob is expanded ^echo $"~/($name)/*" # this isn't expanded ``` - Ndots are now supported for the head of an external command (`^.../foo` works) - Glob values are now supported for head/args of an external command, and expanded appropriately: ```nushell ^("~/.cargo/bin/exa" | into glob) # the tilde is expanded ^echo ("*.txt" | into glob) # this glob is expanded ``` - `run-external` now works more like any other command, without expecting a special call convention for its args: ```nushell run-external echo "'foo'" # before PR: 'foo' # after PR: foo run-external echo "*.txt" # before PR: (glob is expanded) # after PR: *.txt ``` # Tests + Formatting Lots of tests added and cleaned up. Some tests that weren't active on Windows changed to use `nu --testbin cococo` so that they can work. Added a test for Linux only to make sure tilde expansion of commands works, because changing `HOME` there causes `~` to reliably change. - 🟢 `toolkit fmt` - 🟢 `toolkit clippy` - 🟢 `toolkit test` - 🟢 `toolkit test stdlib` # After Submitting - [ ] release notes: make sure to mention the new syntaxes that are supported |
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nu-parser, the Nushell parser
Nushell's parser is a type-directed parser, meaning that the parser will use type information available during parse time to configure the parser. This allows it to handle a broader range of techniques to handle the arguments of a command.
Nushell's base language is whitespace-separated tokens with the command (Nushell's term for a function) name in the head position:
head1 arg1 arg2 | head2
Lexing
The first job of the parser is to a lexical analysis to find where the tokens start and end in the input. This turns the above into:
<item: "head1">, <item: "arg1">, <item: "arg2">, <pipe>, <item: "head2">
At this point, the parser has little to no understanding of the shape of the command or how to parse its arguments.
Lite parsing
As Nushell is a language of pipelines, pipes form a key role in both separating commands from each other as well as denoting the flow of information between commands. The lite parse phase, as the name suggests, helps to group the lexed tokens into units.
The above tokens are converted the following during the lite parse phase:
Pipeline:
Command #1:
<item: "head1">, <item: "arg1">, <item: "arg2">
Command #2:
<item: "head2">
Parsing
The real magic begins to happen when the parse moves on to the parsing stage. At this point, it traverses the lite parse tree and for each command makes a decision:
- If the command looks like an internal/external command literal: e.g.
fooor/usr/bin/ls, it parses it as an internal or external command - Otherwise, it parses the command as part of a mathematical expression
Types/shapes
Each command has a shape assigned to each of the arguments it reads in. These shapes help define how the parser will handle the parse.
For example, if the command is written as:
where $x > 10
When the parsing happens, the parser will look up the where command and find its Signature. The Signature states what flags are allowed and what positional arguments are allowed (both required and optional). Each argument comes with a Shape that defines how to parse values to get that position.
In the above example, if the Signature of where said that it took three String values, the result would be:
CallInfo:
Name: `where`
Args:
Expression($x), a String
Expression(>), a String
Expression(10), a String
Or, the Signature could state that it takes in three positional arguments: a Variable, an Operator, and a Number, which would give:
CallInfo:
Name: `where`
Args:
Expression($x), a Variable
Expression(>), an Operator
Expression(10), a Number
Note that in this case, each would be checked at compile time to confirm that the expression has the shape requested. For example, "foo" would fail to parse as a Number.
Finally, some Shapes can consume more than one token. In the above, if the where command stated it took in a single required argument, and that the Shape of this argument was a MathExpression, then the parser would treat the remaining tokens as part of the math expression.
CallInfo:
Name: `where`
Args:
MathExpression:
Op: >
LHS: Expression($x)
RHS: Expression(10)
When the command runs, it will now be able to evaluate the whole math expression as a single step rather than doing any additional parsing to understand the relationship between the parameters.
Making space
As some Shapes can consume multiple tokens, it's important that the parser allow for multiple Shapes to coexist as peacefully as possible.
The simplest way it does this is to ensure there is at least one token for each required parameter. If the Signature of the command says that it takes a MathExpression and a Number as two required arguments, then the parser will stop the math parser one token short. This allows the second Shape to consume the final token.
Another way that the parser makes space is to look for Keyword shapes in the Signature. A Keyword is a word that's special to this command. For example in the if command, else is a keyword. When it is found in the arguments, the parser will use it as a signpost for where to make space for each Shape. The tokens leading up to the else will then feed into the parts of the Signature before the else, and the tokens following are consumed by the else and the Shapes that follow.