Enum BuildError 

#[non_exhaustive]
pub enum BuildError {
    EmptyTree,
    UnclosedNodes,
    UnbalancedFinish,
    TokenOutsideNode,
    MultipleRoots,
}

Why a Builder could not produce a tree.

The builder never panics on misuse; it records the first fault and surfaces it from Builder::finish. Each variant names a specific imbalance between the start_node / token / finish_node calls and what a caller should change.

Examples

use syntax_lang::{BuildError, Builder};

// Closing a node that was never opened.
let mut b = Builder::<&str>::new();
b.finish_node();
assert_eq!(b.finish(), Err(BuildError::UnbalancedFinish));

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

EmptyTree

finish was called before any node was started, so there is no tree to return. Start a root node before finishing.

UnclosedNodes

finish was called while nodes were still open. Balance every start_node with a finish_node before finishing.

UnbalancedFinish

finish_node was called with no open node. Remove the extra close, or add the missing start_node.

TokenOutsideNode

token was called before any node was started. A tree’s root must be a node; open one before pushing tokens.

MultipleRoots

A second root node was started after the first root was already closed. A tree has exactly one root; wrap the roots in an enclosing node instead.

Trait Implementations

impl Clone for BuildError

fn clone(&self) -> BuildError

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for BuildError

impl Debug for BuildError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for BuildError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for BuildError

impl Error for BuildError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl PartialEq for BuildError

fn eq(&self, other: &BuildError) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl StructuralPartialEq for BuildError