007916c2c1
# Description
Added a few syntax errors in ints and strings, changed parser to stop
and show that error rather than continue trying to parse those tokens as
some other shape. However, I don't see how to push this direction much
further, and most of the classic confusing errors can't be changed.
Flagged as WIP for the moment, but passes all checks and works better
than current release:
1. I have yet to figure out how to make these errors refer back to the
book, as I see some other errors do.
2. How to give syntax error when malformed int is first token in line?
Currently parsed as external command, user gets confusing error message.
3. Would like to be more strict with *decimal* int literals (lacking,
e.g, `0x' prefix). Need to tinker more with the order of parse shape
calls, currently, float is tried after int, so '1.4' has to be passed.
_(Description of your pull request goes here. **Provide examples and/or
screenshots** if your changes affect the user experience.)_
```bash
〉"\z"
Error:
╭─[entry #3:1:1]
1 │ "\z"
· ─┬─
· ╰── Syntax error in string, unrecognized character after escape '\'.
╰────
```
Canonic presentation of a syntax error.
```bash
〉" \u{01ffbogus}"
Error:
× Invalid syntax
╭─[entry #2:1:1]
1 │ " \u{01ffbogus}"
· ───────┬──────
· ╰── Syntax error in string, expecting 1 to 6 hex digits in unicode escape '\u{X...}', max value 10FFFF.
╰────
```
Malformed unicode escape in string, flagged as error.
String parse can be opinionated, it's the last shape tried.
```bash
〉0x22bogus
Error: nu:🐚:external_command (link)
× External command failed
╭─[entry #4:1:1]
1 │ 0x22bogus
· ────┬────
· ╰── executable was not found
╰────
help: No such file or directory (os error 2)
```
A *correct* number in first token would be evaluated, but an *incorrect*
one is treated as external command? Confusing to users.
```bash
〉0 + 0x22bogus
Error:
× Invalid syntax
╭─[entry #5:1:1]
1 │ 0 + 0x22bogus
· ────┬────
· ╰── Syntax error in int, invalid digits in radix 16 int.
╰────
```
Can give syntax error if token is unambiguously int literal. e.g has 0b
or 0x prefix, could not be a float.
```bash
〉0 + 098bogus
Error: nu::parser::unsupported_operation (link)
× Types mismatched for operation.
╭─[entry #6:1:1]
1 │ 0 + 098bogus
· ┬ ┬ ────┬───
· │ │ ╰── string
· │ ╰── doesn't support these values.
· ╰── int
╰────
help: Change int or string to be the right types and try again.
```
But *decimal* literal (no prefix) can't be too strict. Parser is going
to try float later. So '1.4' must be passed.
# User-Facing Changes
First and foremost, more specific error messages for typos in string and
int literals. Probably improves interactive user experience.
But a script that was causing and then checking for specific error might
notice a different error message.
_(List of all changes that impact the user experience here. This helps
us keep track of breaking changes.)_
# Tests + Formatting
Added (positive and negative unit tests in `cargo test -p nu-parser`.
Didn't add integration tests.
Make sure you've run and fixed any issues with these commands:
- [x] `cargo fmt --all -- --check` to check standard code formatting
(`cargo fmt --all` applies these changes)
- [x] `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- [x] `cargo test --workspace` to check that all tests pass
# After Submitting
If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
---------
Co-authored-by: Stefan Holderbach <sholderbach@users.noreply.github.com>
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| .. | ||
| src | ||
| tests | ||
| Cargo.toml | ||
| LICENSE | ||
| README.md | ||
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.