openmoat_core/

policy.rs

//! Policy file model, loading and linting (docs/POLICY.md).

use std::collections::{BTreeMap, BTreeSet};

/// Fallback verdicts when no rule matches: one verdict for everything, or a map
/// from action kind (`shell`, `fs.read`, `fs.write`, `net`, `fetch`,
/// `web.search`, `tool.unknown`, `env.read`, `env.set`, `mcp`, or `"*"`) to a verdict; a `fetch`
/// without its own entry takes the `net` one. This is how "outbound network is
/// deny-by-default" is expressed, because deny rules are absolute and cannot
/// be punched through by allow rules (ADR-002).
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(untagged)]
pub enum Defaults {
    /// The same verdict for every kind.
    All(Verdict),
    /// A verdict per kind name (`net`, `fs.read`, …), with `*` as the fallback.
    PerKind(BTreeMap<String, Verdict>),
}

impl Defaults {
    /// Verdict and synthetic rule id (`default` or `default.<kind>`) for a kind.
    #[must_use]
    pub fn for_kind(&self, kind: Kind) -> (Verdict, String) {
        match self {
            Self::All(v) => (*v, "default".to_owned()),
            Self::PerKind(map) => kind
                .rule_kinds()
                .iter()
                .find_map(|k| map.get(k.as_str()).map(|v| (*v, format!("default.{k}"))))
                .unwrap_or_else(|| {
                    (
                        map.get("*").copied().unwrap_or(Verdict::Review),
                        "default".to_owned(),
                    )
                }),
        }
    }

    /// The default for an atom no rule matched: [`Self::for_kind`], except that a
    /// word that only looks like a host is no network evidence and gets
    /// [`Self::unclassified`] (ADR-025).
    #[must_use]
    pub fn for_atom(&self, atom: &crate::AtomicAction) -> (Verdict, String) {
        match atom {
            crate::AtomicAction::NetWord { .. } => (self.unclassified(), "default".to_owned()),
            _ => self.for_kind(atom.kind()),
        }
    }

    /// What OpenMoat gives a call it cannot classify, or a word that only looks
    /// like a host: `defer` under a catch-all (`"*"`) of `allow` or `defer`, else
    /// `review` (ADR-025). Never `allow`, and never a deny nothing named.
    #[must_use]
    pub fn unclassified(&self) -> Verdict {
        let catch_all = match self {
            Self::All(v) => *v,
            Self::PerKind(map) => map.get("*").copied().unwrap_or(Verdict::Review),
        };
        catch_all.clamp(Verdict::Defer, Verdict::Review)
    }
}

use serde::{Deserialize, Serialize};
use thiserror::Error;

use crate::kind::Kind;
use crate::pattern::{GlobPattern, ShellPattern};
use crate::secret::{self, Secret};
use crate::staging::{self, StagingSettings};
use crate::taint::{self, TaintSettings};
use crate::verdict::Verdict;

mod env_name;
mod hook_only;
mod old_names;
mod require;
mod text;

pub use env_name::env_name_problem;
pub use require::{Require, RequiredBy, RequiredLevel, Requirement, RunBoundary};
pub use text::{TITLE_MAX_CHARS, WHY_MAX_CHARS};

pub use old_names::OldNames;

/// The policy schema version (`version:`) this build reads; any other is an error.
pub const SUPPORTED_VERSION: u32 = 1;

/// Why a policy file cannot be used. Any of these keeps `guard` from deciding.
///
/// Messages include their cause, so no variant also exposes it as `source`:
/// a chained report (`{:#}`) would print it twice.
#[derive(Debug, Error)]
#[non_exhaustive]
pub enum PolicyError {
    /// The file is not valid YAML or does not fit the schema.
    #[error("policy parse error: {0}")]
    Parse(crate::yaml::Error),
    /// The `version` key names a schema this build does not know.
    #[error("unsupported policy version {found}; this build supports {supported}")]
    Version {
        /// The version in the file.
        found: u32,
        /// The version this build supports.
        supported: u32,
    },
    /// Two rule groups share an id.
    #[error("duplicate rule id `{0}`")]
    DuplicateId(String),
    /// A rule group lists no patterns.
    #[error("rule `{0}` has no patterns")]
    EmptyRule(String),
    /// A pattern is empty (or only `!`/`$`).
    #[error("empty pattern")]
    EmptyPattern,
    /// A glob does not compile.
    #[error("bad glob `{pattern}`: {error}")]
    BadGlob {
        /// The pattern as written.
        pattern: String,
        /// The glob compiler's explanation.
        error: globset::Error,
    },
    /// A shell pattern does not tokenise (unbalanced quotes, a here-document).
    #[error("bad shell pattern `{pattern}` (unbalanced quotes?)")]
    BadShellPattern {
        /// The pattern as written.
        pattern: String,
    },
    /// The file has both `ask:` and `review:` (ADR-053): `ask` is the old name
    /// of `review`, and which list was meant cannot be told.
    #[error(
        "the policy has both `{old}:` and `{new}:`; `{old}` is the old name of `{new}`: \
         move the `{old}:` rules into `{new}:` (`openmoat policy upgrade` renames a policy \
         that has only `{old}:`)"
    )]
    OldAndNewName {
        /// The old key.
        old: &'static str,
        /// The current key.
        new: &'static str,
    },
    /// A rule group or `executables` entry is invalid; `problem` says why.
    #[error("rule `{rule}`: {problem}")]
    Rule {
        /// Rule id, or `executables.<name>`.
        rule: String,
        /// What is wrong.
        problem: String,
    },
}

/// One named group of patterns. A group matches when **any** of its patterns
/// matches the atomic action of the corresponding kind.
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct RuleGroup {
    /// Stable identifier shown in decisions and the audit log.
    pub id: String,
    /// Text prepended to the reason when this group decides.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub reason: Option<String>,
    /// What the rule stops or holds, in the person's words ("reading your SSH
    /// private key"): the first line of the message an agent and its person
    /// see when this group denies or holds a call (ADR-059). One line.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub title: Option<String>,
    /// Why the rule exists, in one line, shown under [`Self::title`].
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub why: Option<String>,
    /// Shell patterns (token prefixes, `*`, `!`, trailing `$`).
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub shell: Vec<String>,
    /// Path globs for file reads.
    #[serde(default, rename = "fs.read", skip_serializing_if = "Vec::is_empty")]
    pub fs_read: Vec<String>,
    /// Path globs for file writes.
    #[serde(default, rename = "fs.write", skip_serializing_if = "Vec::is_empty")]
    pub fs_write: Vec<String>,
    /// Host globs for any network access, fetches included.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub net: Vec<String>,
    /// Host globs for read-only fetches by a host's fetch tool only.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub fetch: Vec<String>,
    /// Variable-name globs for reads.
    #[serde(default, rename = "env.read", skip_serializing_if = "Vec::is_empty")]
    pub env_read: Vec<String>,
    /// Variable-name globs for sets.
    #[serde(default, rename = "env.set", skip_serializing_if = "Vec::is_empty")]
    pub env_set: Vec<String>,
    /// MCP tool-name globs.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub mcp: Vec<String>,
    /// Applied by the hook only (ADR-034): OS layers leave this group's
    /// `fs.read` and `fs.write` paths to the other rules, so a build tool a
    /// sandboxed command runs can still read them. `deny` groups only, never
    /// with `net` or `fetch`.
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub hook_only: bool,
}

impl RuleGroup {
    /// The patterns this group lists for `kind`.
    #[must_use]
    pub fn patterns(&self, kind: Kind) -> &[String] {
        match kind {
            Kind::Shell => &self.shell,
            Kind::FsRead => &self.fs_read,
            Kind::FsWrite => &self.fs_write,
            Kind::Net => &self.net,
            Kind::Fetch => &self.fetch,
            // A query or an unknown tool names no host or path to match; only
            // `defaults` decide them.
            Kind::WebSearch | Kind::UnknownTool => &[],
            Kind::EnvRead => &self.env_read,
            Kind::EnvSet => &self.env_set,
            Kind::Mcp => &self.mcp,
        }
    }

    fn is_empty(&self) -> bool {
        Kind::ALL.iter().all(|k| self.patterns(*k).is_empty())
    }

    /// Check that every pattern of this group parses, naming the group in the
    /// error: what [`Policy::lint`] does for each group.
    ///
    /// # Errors
    /// [`PolicyError::Rule`] for the first pattern that does not parse.
    pub fn check_patterns(&self) -> Result<(), PolicyError> {
        for kind in Kind::ALL {
            for p in self.patterns(kind) {
                let compiled = if kind == Kind::Shell {
                    ShellPattern::compile(p).map(drop)
                } else {
                    GlobPattern::compile(p, false).map(drop)
                };
                compiled.map_err(|e| rule_err(&self.id, &e))?;
            }
        }
        Ok(())
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Scope {
    #[serde(default = "default_roots")]
    pub project_roots: Vec<String>,
}

fn default_roots() -> Vec<String> {
    vec![".".to_owned()]
}

impl Default for Scope {
    fn default() -> Self {
        Self {
            project_roots: default_roots(),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum ApprovalChannel {
    Terminal,
    Telegram,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum RememberScope {
    Once,
    Session,
    Permanent,
}

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Approval {
    #[serde(default = "default_channel")]
    pub channel: ApprovalChannel,
    #[serde(default = "default_remember")]
    pub remember: RememberScope,
    #[serde(default = "default_timeout")]
    pub timeout_s: u32,
}

fn default_channel() -> ApprovalChannel {
    ApprovalChannel::Terminal
}
fn default_remember() -> RememberScope {
    RememberScope::Session
}
fn default_timeout() -> u32 {
    300
}

impl Default for Approval {
    fn default() -> Self {
        Self {
            channel: default_channel(),
            remember: default_remember(),
            timeout_s: default_timeout(),
        }
    }
}

/// The policy document (`policy.yaml`), as written by users.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Policy {
    /// Schema version; only 1 is supported.
    pub version: u32,
    /// Verdict when no rule matches.
    #[serde(default = "default_verdict")]
    pub defaults: Defaults,
    /// Reserved for multi-root projects; parsed so existing files stay valid,
    /// not yet consulted (`policy lint` warns).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub scope: Option<Scope>,
    /// Evaluated first; a match is final.
    #[serde(default)]
    pub deny: Vec<RuleGroup>,
    /// Evaluated after `deny`.
    #[serde(default)]
    pub allow: Vec<RuleGroup>,
    /// Evaluated after `allow`: calls a person reviews. Read from `ask:` too,
    /// its name before ADR-053 ([`OldNames`]).
    #[serde(default, alias = "ask")]
    pub review: Vec<RuleGroup>,
    /// Evaluated after `review`: calls the agent's own permission flow decides
    /// (ADR-025). Absent in policies written before it existed.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub defer: Vec<RuleGroup>,
    /// Reserved for the kernel's own approval prompt; parsed so existing files
    /// stay valid, not yet consulted (`policy lint` warns).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub approval: Option<Approval>,
    /// Basename → allowed absolute paths (defeats PATH poisoning).
    #[serde(default)]
    pub executables: BTreeMap<String, Vec<String>>,
    /// What the operating-system layers OpenMoat configures need beyond the rules
    /// (ADR-018). Absent in policies written before it existed.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub sandbox: Option<SandboxSettings>,
    /// Secrets `moat proxy` keeps from the agent and injects for one host each.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub secrets: Vec<Secret>,
    /// What session taint protects beyond the built-in list. Absent in older policies.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub taint: Option<TaintSettings>,
    /// When a session counts as having collected files outside the project
    /// (ADR-061, proposed): the `@staging-egress` atom's thresholds. Absent in
    /// older policies, which means the defaults.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub staging: Option<StagingSettings>,
    /// Trust a repository policy only when its detached signature
    /// (`policy.yaml.sig`) verifies against a key the person trusted (ADR-031):
    /// a signed one needs no `moat trust`, and an unsigned one is not trusted even
    /// after `moat trust`. Off by default: then only `moat trust` lets a
    /// repository policy allow.
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub require_signed_repo_policy: bool,
    /// How `moat mcp proxy` treats tool definitions (ADR-032). Absent in older policies.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub mcp: Option<McpSettings>,
    /// The levels `openmoat policy check-diff` reports its content checks at
    /// (ADR-055). Absent in older policies: each check's own level.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub check_diff: Option<crate::diffscan::Settings>,
    /// The least protection level each agent must be at for `openmoat guard`
    /// to decide its calls; below it, every call is denied
    /// (`protection-required`, ADR-064). Absent in older policies and the
    /// default: nothing is required.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub require: Option<Require>,
    /// The `require:` sections of the repository policy and the packs merged
    /// in ([`Policy::add_requirement`]), read with [`Self::require`] by
    /// [`Policy::required_for`], which takes the strictest: they raise a
    /// level, never lower one. Never read from or written to a file.
    #[serde(skip)]
    pub require_added: Vec<(RequiredBy, Require)>,
    /// Review rules merged in from a repository policy ([`crate::RepoPolicy`],
    /// ADR-022) or a policy pack (ADR-031). Tried after `deny` and before
    /// `allow`, so a repository can make an action the user allows need review.
    /// Never read from or written to a file, and not lowered to OS layers, which
    /// are generated from the user policy alone.
    #[serde(skip)]
    pub repo_review: Vec<RuleGroup>,
    /// Where the file used `ask`, the old name of `review` (ADR-053), which
    /// `policy lint` warns about. Set by [`Policy::parse`]; never written.
    #[serde(skip)]
    pub old_names: OldNames,
}

/// The `sandbox:` section (ADR-018, ADR-019).
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct SandboxSettings {
    /// Paths (directories or files) the OS layers let commands read although no
    /// allow rule covers them: system and toolchain directories every build
    /// reads. The hook decision ignores them, and deny rules win over them in
    /// every layer. Absolute or `~/…`, never a glob.
    #[serde(default)]
    pub read_roots: Vec<String>,
    /// The loopback port `moat proxy` listens on and the host sandboxes send
    /// their commands' traffic to; absent, the CLI's default.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub proxy_port: Option<std::num::NonZeroU16>,
    /// Let `moat proxy` forward a TLS `ClientHello` that carries an encrypted
    /// server name (ECH, ESNI). Off, such a tunnel is refused: the server acts
    /// on the encrypted name, which may be another site than the allowed host.
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub proxy_allow_ech: bool,
    /// Let `moat proxy` serve a request that carries no session credential,
    /// with no session (ADR-044). Off, such a request gets 407: a session's
    /// taint and connection share cannot be escaped by sending no credential,
    /// and other local processes cannot use the proxy. `moat run` ignores it.
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub proxy_serve_without_credential: bool,
    /// Days a package version must have been published before the package
    /// managers `moat run` starts install it (ADR-030); `0` turns this off,
    /// absent is 7 days ([`Policy::package_min_release_age_days`]).
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub package_min_release_age_days: Option<u16>,
    /// Names of inherited environment variables `openmoat run` passes on
    /// under `require.run: full-boundary`, beyond its own list and the
    /// agent's (ADR-077). Names only, never a pattern. Read from the person's
    /// own policy alone: a repository policy or a pack has no `sandbox:`.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub env_allow: Vec<String>,
    /// What `openmoat run`'s Lightweight tier on Linux without a network
    /// namespace grants at the top of the project (ADR-090): `protected`
    /// grants it entry by entry, so nothing can be created there and `.env`,
    /// `.git` and `.moat` stay covered; `writable` grants it whole, so new
    /// entries and save-by-rename work there and those paths are open to the
    /// agent's commands. Never read by the Isolated tier or the network
    /// namespace. Read from the person's own policy alone: a repository policy
    /// or a pack has no `sandbox:`.
    #[serde(default, skip_serializing_if = "ProjectTop::is_protected")]
    pub project_top: ProjectTop,
}

/// `sandbox.project_top` (ADR-090).
#[derive(Debug, Clone, Copy, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum ProjectTop {
    /// Granted entry by entry: the policy's denies at the top hold.
    #[default]
    Protected,
    /// Granted whole: the top is writable, and `.env` and `.git/hooks` there
    /// are open to the agent's commands.
    Writable,
}

impl ProjectTop {
    /// Whether this is the default, [`ProjectTop::Protected`].
    #[must_use]
    pub fn is_protected(&self) -> bool {
        *self == Self::Protected
    }
}

/// The `mcp:` section (ADR-032).
#[derive(Debug, Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct McpSettings {
    /// Pin every tool `moat mcp proxy` sees from a server it has no pins for,
    /// as it is, instead of holding them until `moat mcp accept`. Off by
    /// default: a server that is malicious on first contact would get its
    /// tool descriptions pinned as good.
    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
    pub trust_first_sight: bool,
    /// How an MCP call that only opens or reads one web page is decided
    /// (ADR-047): `fetch` (absent) as a `fetch` of its host, like `WebFetch`;
    /// `net` as a `net` connection, which the default policy denies for
    /// unlisted hosts.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub browser_open: Option<BrowserOpen>,
    /// MCP servers, by the name `openmoat mcp proxy --server` gives them,
    /// whose data flows are trusted (ADR-058): text such a server returned may
    /// reach another server's tool that writes or sends, and a call to such a
    /// server may carry another server's text, without a `mcp-cross-server`
    /// review.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub flow_trusted: Vec<String>,
}

/// `mcp.browser_open`: the kind a read-only page open of an MCP tool is decided as.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum BrowserOpen {
    /// A `fetch` of the page's host (the default).
    Fetch,
    /// A `net` connection to the page's host, as any other MCP URL argument.
    Net,
}

/// The release age `moat run` requires of new package versions when the policy
/// does not say (ADR-030).
pub const DEFAULT_PACKAGE_MIN_RELEASE_AGE_DAYS: u16 = 7;

impl Policy {
    /// The days a package version must have been published before `moat run`
    /// lets npm and uv install it; `0` is off.
    #[must_use]
    pub fn package_min_release_age_days(&self) -> u16 {
        self.sandbox
            .as_ref()
            .and_then(|s| s.package_min_release_age_days)
            .unwrap_or(DEFAULT_PACKAGE_MIN_RELEASE_AGE_DAYS)
    }

    /// What `openmoat run` without a network namespace grants at the project's
    /// top (`sandbox.project_top`, ADR-090); [`ProjectTop::Protected`] unless
    /// the person's own policy says otherwise.
    #[must_use]
    pub fn project_top(&self) -> ProjectTop {
        self.sandbox
            .as_ref()
            .map(|s| s.project_top)
            .unwrap_or_default()
    }

    /// Whether `moat mcp proxy` pins a new server's tools without a person
    /// accepting them (`mcp.trust_first_sight`, ADR-032).
    #[must_use]
    pub fn trust_mcp_first_sight(&self) -> bool {
        self.mcp.as_ref().is_some_and(|m| m.trust_first_sight)
    }

    /// Whether an MCP call that only opens a web page is decided as a `fetch`
    /// (`mcp.browser_open`, ADR-047): yes unless the policy says `net`.
    #[must_use]
    pub fn browser_open_is_fetch(&self) -> bool {
        self.mcp.as_ref().and_then(|m| m.browser_open) != Some(BrowserOpen::Net)
    }

    /// The MCP servers whose data flows need no `mcp-cross-server` review
    /// (`mcp.flow_trusted`, ADR-058).
    #[must_use]
    pub fn mcp_flow_trusted(&self) -> &[String] {
        self.mcp.as_ref().map_or(&[], |m| m.flow_trusted.as_slice())
    }
}

fn default_verdict() -> Defaults {
    Defaults::All(Verdict::Review)
}

impl Policy {
    /// Parse and lint a policy document. Pure: takes the YAML text.
    pub fn parse(yaml: &str) -> Result<Self, PolicyError> {
        let old_names = old_names::find(yaml)?;
        let mut policy: Self = crate::yaml::from_str(yaml).map_err(PolicyError::Parse)?;
        policy.old_names = old_names;
        policy.lint()?;
        Ok(policy)
    }

    /// Structural validation independent of any environment: [`Self::lint_structure`]
    /// and every pattern's syntax ([`RuleGroup::check_patterns`]).
    pub fn lint(&self) -> Result<(), PolicyError> {
        self.lint_structure()?;
        self.groups().try_for_each(RuleGroup::check_patterns)
    }

    /// [`Self::lint`] without parsing each pattern again, for a policy that
    /// gained rule groups after a full lint, such as a merge of rules each
    /// checked when they were read (a repository policy, a pack, `openmoat allow`
    /// rules): the new groups' patterns are checked with
    /// [`RuleGroup::check_patterns`], and nothing else needs reparsing. Parsing
    /// every pattern costs more than the rest of the lint together, and
    /// [`crate::CompiledPolicy::compile`] reports a bad one in any case.
    pub fn lint_structure(&self) -> Result<(), PolicyError> {
        if self.version != SUPPORTED_VERSION {
            return Err(PolicyError::Version {
                found: self.version,
                supported: SUPPORTED_VERSION,
            });
        }
        let mut ids = BTreeSet::new();
        for group in self.groups() {
            if group.id.trim().is_empty() {
                return Err(PolicyError::Rule {
                    rule: "<unnamed>".into(),
                    problem: "missing id".into(),
                });
            }
            if !ids.insert(group.id.clone()) {
                return Err(PolicyError::DuplicateId(group.id.clone()));
            }
            if group.is_empty() {
                return Err(PolicyError::EmptyRule(group.id.clone()));
            }
            text::check(group)?;
        }
        hook_only::check(self)?;
        for (name, paths) in &self.executables {
            if paths.is_empty() {
                return Err(PolicyError::Rule {
                    rule: format!("executables.{name}"),
                    problem: "no paths listed".into(),
                });
            }
            if let Some(bad) = paths.iter().find(|p| !crate::paths::is_absolute(p)) {
                return Err(PolicyError::Rule {
                    rule: format!("executables.{name}"),
                    problem: format!("`{bad}` is not an absolute path"),
                });
            }
        }
        for root in self.sandbox.iter().flat_map(|s| &s.read_roots) {
            lint_read_root(root)?;
        }
        for name in self.sandbox.iter().flat_map(|s| &s.env_allow) {
            if let Some(problem) = env_name_problem(name) {
                return Err(PolicyError::Rule {
                    rule: "sandbox.env_allow".to_owned(),
                    problem: format!("`{name}` {problem}"),
                });
            }
        }
        taint::check(self.taint.as_ref())?;
        staging::check(self.staging.as_ref())?;
        crate::diffscan::check(self.check_diff.as_ref())?;
        require::check(self.require.as_ref())?;
        for (_, added) in &self.require_added {
            require::check(Some(added))?;
        }
        secret::check(&self.secrets)
    }

    /// Every rule group, in the order the engine tries the lists.
    fn groups(&self) -> impl Iterator<Item = &RuleGroup> {
        self.deny
            .iter()
            .chain(&self.repo_review)
            .chain(&self.allow)
            .chain(&self.review)
            .chain(&self.defer)
    }

    /// Number of rule groups in `deny`, `allow` and `review`.
    #[must_use]
    pub fn rule_count(&self) -> (usize, usize, usize) {
        (self.deny.len(), self.allow.len(), self.review.len())
    }
}

/// An OS layer takes a read root literally, and a root that is the disk or the
/// home directory would undo every default deny.
fn lint_read_root(root: &str) -> Result<(), PolicyError> {
    let trimmed = root.trim_end_matches(['/', '\\']);
    let problem = if !(crate::paths::is_absolute(root) || root.starts_with("~/")) {
        "must be absolute or start with `~/`"
    } else if root.contains(['*', '?', '[', ']', '{', '}', '!', '$']) {
        "must be a plain path, not a glob or a variable"
    } else if root.split(['/', '\\']).any(|s| s == "." || s == "..") {
        "must not contain `.` or `..` segments"
    } else if trimmed == "~" {
        "must not be the home directory"
    } else if trimmed.is_empty() || (trimmed.len() == 2 && trimmed.ends_with(':')) {
        "must not be a filesystem root"
    } else {
        return Ok(());
    };
    Err(PolicyError::Rule {
        rule: "sandbox.read_roots".to_owned(),
        problem: format!("`{root}` {problem}"),
    })
}

fn rule_err(rule: &str, e: &PolicyError) -> PolicyError {
    PolicyError::Rule {
        rule: rule.to_owned(),
        problem: e.to_string(),
    }
}

#[cfg(test)]
mod tests;