fix(acl): refuse capabilities the census cannot see, and name the failed check

tauri-build loads capabilities/**/*.{json,toml,json5} plus inline
app.security.capabilities from any tauri config or TAURI_CONFIG, but the
census read only top-level capabilities/*.json, so a .toml, a
subdirectory or an inline capability could over-grant a window with a
green build. build.rs now fails on any of those, on a JSON5/TOML tauri
config it cannot read, and on a `webviews` or `remote` key in a
capability file. OS/editor junk (.DS_Store, swap files) that tauri never
loads is skipped in capabilities/ and permissions/. Each failure is
headed by the check that failed rather than always "capabilities do not
match generate_handler!".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

app/src-tauri/src/command_census.rs

@@ -75,6 +75,16 @@ pub struct CapabilityFile {
 pub fn capability_file(name: &str, json: &str) -> Result<CapabilityFile, String> {
     let value: serde_json::Value =
         serde_json::from_str(json).map_err(|e| format!("{name}: not valid JSON: {e}"))?;
+    // `webviews` would extend the grants to webviews by label (the browser-view pop-out is
+    // meant to be in no capability), and `remote` would extend them to a remote origin. The
+    // census reasons about `windows` only, so either key is refused rather than half-checked.
+    for key in ["webviews", "remote"] {
+        if value.get(key).is_some() {
+            return Err(format!(
+                "{name}: `{key}` is not allowed; capabilities here are scoped by `windows` only"
+            ));
+        }
+    }
     let windows = value["windows"]
         .as_array()
         .ok_or_else(|| format!("{name}: `windows` must be an array"))?
@@ -105,6 +115,79 @@ pub fn capability_file(name: &str, json: &str) -> Result<CapabilityFile, String>
     Ok(CapabilityFile { name: name.to_string(), windows, bare })
 }
 
+/// Why an entry directly under `capabilities/` cannot be a capability the census reads, or
+/// `None` if it is one (a top-level `*.json` file). tauri-build loads `capabilities/**/*` with
+/// the extensions `json`, `toml` and (with a feature) `json5`, subdirectories included; the
+/// census reads only top-level JSON, so anything else tauri might load is refused rather than
+/// left for tauri to grant from unchecked. OS and editor junk, which tauri never loads, is the
+/// caller's to skip first (see [`is_os_junk`]).
+pub fn stray_capability_entry(name: &str, is_file: bool) -> Option<String> {
+    if !is_file {
+        return Some(format!(
+            "capabilities/{name} is not a regular file; tauri loads capabilities from \
+             subdirectories too, so every capability must be a top-level capabilities/*.json"
+        ));
+    }
+    if name.ends_with(".json") {
+        return None;
+    }
+    Some(format!(
+        "capabilities/{name} is not a .json file; tauri may load it (it reads .toml and .json5 \
+         too) but the census cannot check it, so every capability must be a top-level \
+         capabilities/*.json"
+    ))
+}
+
+/// Files the OS or an editor drops next to real ones (`.DS_Store`, `Thumbs.db`, `desktop.ini`,
+/// Vim swap files, `name~` backups). tauri-build loads only `json`/`toml`/`json5` from
+/// `capabilities/` and `permissions/`, so a junk name with one of those extensions (an Emacs
+/// `.#default.json` lock, a macOS `._default.json`) is *not* junk: tauri would try to load it,
+/// and the caller must refuse it.
+pub fn is_os_junk(name: &str) -> bool {
+    let loadable = [".json", ".json5", ".toml"].iter().any(|e| name.ends_with(e));
+    !loadable
+        && (matches!(name, ".DS_Store" | "Thumbs.db" | "desktop.ini")
+            || name.ends_with(".swp")
+            || name.ends_with(".swo")
+            || name.ends_with('~'))
+}
+
+/// Which files next to `Cargo.toml` tauri reads as its config: `tauri.conf.json[5]`,
+/// `Tauri.toml` and the per-platform `tauri.<platform>.conf.json[5]` / `Tauri.<platform>.toml`
+/// (tauri-utils `config/parse.rs`). `Some(true)` = JSON the census can read, `Some(false)` = a
+/// format it cannot (JSON5/TOML), `None` = not a tauri config file.
+pub fn tauri_config_file(name: &str) -> Option<bool> {
+    if name.starts_with("tauri.") && name.ends_with(".conf.json") {
+        Some(true)
+    } else if (name.starts_with("tauri.") && name.ends_with(".conf.json5"))
+        || (name.starts_with("Tauri.") && name.ends_with(".toml"))
+    {
+        Some(false)
+    } else {
+        None
+    }
+}
+
+/// A problem with a tauri config (a `tauri*.conf.json` file, or the `TAURI_CONFIG` JSON that
+/// tauri-build merges over it), or `None`. `app.security.capabilities` is refused whenever it
+/// is non-empty: an inline object is a capability the census never sees, and a list of
+/// identifiers switches every *other* capability file off, which the census also assumes is
+/// not happening.
+pub fn tauri_config_problem(name: &str, json: &str) -> Option<String> {
+    let value: serde_json::Value = match serde_json::from_str(json) {
+        Ok(v) => v,
+        Err(e) => return Some(format!("{name}: not valid JSON: {e}")),
+    };
+    match value.pointer("/app/security/capabilities") {
+        None | Some(serde_json::Value::Null) => None,
+        Some(serde_json::Value::Array(a)) if a.is_empty() => None,
+        Some(_) => Some(format!(
+            "{name}: app.security.capabilities is not allowed; every capability lives in a \
+             top-level capabilities/*.json file, where the census checks it"
+        )),
+    }
+}
+
 /// Everything that must hold between the handler list and the capability files. Returns every
 /// violation rather than the first, so a batch of forgotten grants is one build failure; an
 /// empty vector is a pass.
@@ -324,6 +407,70 @@ mod tests {
         assert!(capability_file("x.json", "not json").unwrap_err().contains("x.json"));
     }
 
+    #[test]
+    fn webviews_and_remote_keys_are_refused() {
+        let with = |extra: &str| {
+            format!(r#"{{"windows": ["main"], {extra}, "permissions": ["allow-check-docker"]}}"#)
+        };
+        let err = capability_file("d.json", &with(r#""webviews": ["browser-view-*"]"#)).unwrap_err();
+        assert!(err.contains("d.json") && err.contains("`webviews`"), "{err}");
+        let err = capability_file("d.json", &with(r#""remote": {"urls": ["https://*"]}"#)).unwrap_err();
+        assert!(err.contains("`remote`"), "{err}");
+        // Present-but-empty is still refused: the key itself is the widening surface.
+        assert!(capability_file("d.json", &with(r#""webviews": []"#)).is_err());
+    }
+
+    #[test]
+    fn only_top_level_json_files_are_capabilities() {
+        assert_eq!(stray_capability_entry("default.json", true), None);
+        for name in ["extra.toml", "extra.json5", "notes.txt", ".DS_Store"] {
+            let err = stray_capability_entry(name, true).expect(name);
+            assert!(err.contains(name) && err.contains("not a .json file"), "{err}");
+        }
+        let err = stray_capability_entry("sub", false).unwrap();
+        assert!(err.contains("capabilities/sub") && err.contains("not a regular file"), "{err}");
+        // A directory named like a capability is still a directory.
+        assert!(stray_capability_entry("x.json", false).is_some());
+    }
+
+    #[test]
+    fn os_junk_is_recognised_but_never_something_tauri_would_load() {
+        for junk in [".DS_Store", "Thumbs.db", "desktop.ini", ".default.json.swp", ".x.swo", "default.json~"] {
+            assert!(is_os_junk(junk), "{junk}");
+        }
+        for real in ["default.json", "x.toml", "x.json5", ".#default.json", "._default.json", "notes.txt", "extra"] {
+            assert!(!is_os_junk(real), "{real}");
+        }
+    }
+
+    #[test]
+    fn tauri_config_files_are_found_by_name_and_format() {
+        assert_eq!(tauri_config_file("tauri.conf.json"), Some(true));
+        assert_eq!(tauri_config_file("tauri.linux.conf.json"), Some(true));
+        assert_eq!(tauri_config_file("tauri.conf.json5"), Some(false));
+        assert_eq!(tauri_config_file("tauri.windows.conf.json5"), Some(false));
+        assert_eq!(tauri_config_file("Tauri.toml"), Some(false));
+        assert_eq!(tauri_config_file("Tauri.macos.toml"), Some(false));
+        assert_eq!(tauri_config_file("Cargo.toml"), None);
+        assert_eq!(tauri_config_file("build.rs"), None);
+    }
+
+    #[test]
+    fn inline_capabilities_in_the_tauri_config_are_refused() {
+        let ok = r#"{"app": {"security": {"csp": "default-src 'self'"}}}"#;
+        assert_eq!(tauri_config_problem("tauri.conf.json", ok), None);
+        assert_eq!(tauri_config_problem("t", r#"{"app": {"security": {"capabilities": []}}}"#), None);
+        assert_eq!(tauri_config_problem("t", r#"{"build": {"beforeBuildCommand": ""}}"#), None);
+        let inline = r#"{"app": {"security": {"capabilities": [
+            {"identifier": "x", "windows": ["file-viewer-*"], "permissions": ["allow-read-container-file"]}
+        ]}}}"#;
+        let err = tauri_config_problem("tauri.conf.json", inline).unwrap();
+        assert!(err.contains("tauri.conf.json") && err.contains("app.security.capabilities"), "{err}");
+        let by_name = r#"{"app": {"security": {"capabilities": ["default"]}}}"#;
+        assert!(tauri_config_problem("TAURI_CONFIG", by_name).unwrap().contains("TAURI_CONFIG"));
+        assert!(tauri_config_problem("t", "{").unwrap().contains("not valid JSON"));
+    }
+
     #[test]
     fn a_correct_census_has_no_problems() {
         assert_eq!(check(&cmds(THREE), &good_files()), Vec::<String>::new());