graphersal 0.1.1

In-memory graph traversal engine modelled on Apache TinkerPop Gremlin, with a Rhai DSL, optimizer and GraphSON/GraphML I/O
Documentation 
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//! `ScriptGraphTraversalSource::is_mutating()`: whether a script plan contains a mutating step.

use super::*;

impl ScriptGraphTraversalSource {
    /// Whether the traversal contains a mutating step (`add_v`, `property`, `drop`, `merge_v`,
    /// ...), also inside a child traversal. Decided from the plan, before it runs: a `true` plan
    /// may still leave the graph unchanged (no traverser reached the mutating step). Script hosts
    /// use it to warn before re-running a query (the browser playground's refresh); the
    /// terminals use it to take the graph's write lock instead of its read lock.
    ///
    /// Derived from the core's single step -> [`AccessRequest`](crate::graph::AccessRequest)
    /// mapping: the plan is lowered to engine steps (without a graph) and is mutating when some
    /// step requests a write of data or the schema, the same mapping the authorization check
    /// uses.
    ///
    /// A traversal built from a saved query's result (or inside a query's body) is never
    /// mutating on the host graph: it carries the query's read-only restriction, so a writing
    /// step in it fails with `PermissionDenied` before anything runs
    /// (`roadmap/saved-queries.md`, section 4).
    pub fn is_mutating(&self) -> bool {
        if self.access.read_only && !self.private {
            return false;
        }
        self.plan_writes()
    }

    /// Whether the plan as written has a step that writes data or the schema (the mapping
    /// behind [`Self::is_mutating`], without the saved-query exception).
    pub(crate) fn plan_writes(&self) -> bool {
        let mut plan = self.lower::<&TraversalGraph>(true);
        crate::traversal::permission_check::plan_mutates(&mut plan.steps)
    }
}