Patch it all together: use MentatError at top-level.

I elected to keep Tolstoy using `failure::Error`, because Tolstoy
looks rather more like a high-level application (and will continue to
do so for a while) than a production-ready mid- or low-level API.

src/conn.rs

@@ -185,7 +185,7 @@ pub trait Pullable {
 }
 
 pub trait Syncable {
-    fn sync(&mut self, server_uri: &String, user_uuid: &String) -> Result<()>;
+    fn sync(&mut self, server_uri: &String, user_uuid: &String) -> ::std::result::Result<(), ::failure::Error>;
 }
 
 /// Represents an in-progress, not yet committed, set of changes to the store.
@@ -871,8 +871,8 @@ mod tests {
                        .partition_map[":db.part/user"].index;
         let t = format!("[[:db/add {} :db.schema/attribute \"tempid\"]]", next + 1);
 
-        match conn.transact(&mut sqlite, t.as_str()).expect_err("expected transact error").downcast() {
-            Ok(e @ ::mentat_db::DbError { .. }) => {
+        match conn.transact(&mut sqlite, t.as_str()) {
+            Err(MentatError::DbError(e)) => {
                 assert_eq!(e.kind(), ::mentat_db::DbErrorKind::UnrecognizedEntid(next + 1));
             },
             x => panic!("expected db error, got {:?}", x),
@@ -898,8 +898,8 @@ mod tests {
         // we should reject this, because the first ID was provided by the user!
         let t = format!("[[:db/add {} :db.schema/attribute \"tempid\"]]", next);
 
-        match conn.transact(&mut sqlite, t.as_str()).expect_err("expected transact error").downcast() {
-            Ok(e @ ::mentat_db::DbError { .. }) => {
+        match conn.transact(&mut sqlite, t.as_str()) {
+            Err(MentatError::DbError(e)) => {
                 // All this, despite this being the ID we were about to allocate!
                 assert_eq!(e.kind(), ::mentat_db::DbErrorKind::UnrecognizedEntid(next));
             },
@@ -1059,9 +1059,9 @@ mod tests {
 
         // Bad EDN: missing closing ']'.
         let report = conn.transact(&mut sqlite, "[[:db/add \"t\" :db/ident :a/keyword]");
-        match report.expect_err("expected transact to fail for bad edn").downcast() {
-            Ok(edn::ParseError { .. }) => { },
-            Err(x) => panic!("expected EDN parse error, got {:?}", x),
+        match report.expect_err("expected transact to fail for bad edn") {
+            MentatError::EdnParseError(_) => { },
+            x => panic!("expected EDN parse error, got {:?}", x),
         }
 
         // Good EDN.
@@ -1070,9 +1070,9 @@ mod tests {
 
         // Bad transaction data: missing leading :db/add.
         let report = conn.transact(&mut sqlite, "[[\"t\" :db/ident :b/keyword]]");
-        match report.expect_err("expected transact error").downcast() {
-            Ok(edn::ParseError { .. }) => { },
-            Err(x) => panic!("expected EDN parse error, got {:?}", x),
+        match report.expect_err("expected transact error") {
+            MentatError::EdnParseError(_) => { },
+            x => panic!("expected EDN parse error, got {:?}", x),
         }
 
         // Good transaction data.
@@ -1082,8 +1082,8 @@ mod tests {
         // Bad transaction based on state of store: conflicting upsert.
         let report = conn.transact(&mut sqlite, "[[:db/add \"u\" :db/ident :a/keyword]
                                                   [:db/add \"u\" :db/ident :b/keyword]]");
-        match report.expect_err("expected transact error").downcast() {
-            Ok(e @ ::mentat_db::DbError { .. }) => {
+        match report.expect_err("expected transact error") {
+            MentatError::DbError(e) => {
                 match e.kind() {
                     ::mentat_db::DbErrorKind::SchemaConstraintViolation(_) => {},
                     _ => panic!("expected SchemaConstraintViolation"),
@@ -1106,8 +1106,8 @@ mod tests {
         let kw = kw!(:foo/bat);
         let schema = conn.current_schema();
         let res = conn.cache(&mut sqlite, &schema, &kw, CacheDirection::Forward, CacheAction::Register);
-        match res.expect_err("expected cache to fail").downcast() {
-            Ok(MentatError::UnknownAttribute(msg)) => assert_eq!(msg, ":foo/bat"),
+        match res.expect_err("expected cache to fail") {
+            MentatError::UnknownAttribute(msg) => assert_eq!(msg, ":foo/bat"),
             x => panic!("expected UnknownAttribute error, got {:?}", x),
         }
     }

src/entity_builder.rs

@@ -419,8 +419,8 @@ mod testing {
         let mut in_progress = conn.begin_transaction(&mut sqlite).expect("begun successfully");
 
         // This should fail: unrecognized entid.
-        match in_progress.transact_terms(terms, tempids).expect_err("expected transact to fail").downcast() {
-            Ok(e @ mentat_db::DbError { .. }) => {
+        match in_progress.transact_terms(terms, tempids).expect_err("expected transact to fail") {
+            MentatError::DbError(e) => {
                 assert_eq!(e.kind(), mentat_db::DbErrorKind::UnrecognizedEntid(999));
             },
             _ => panic!("Should have rejected the entid."),

src/errors.rs

@@ -14,16 +14,23 @@ use std; // To refer to std::result::Result.
 
 use std::collections::BTreeSet;
 
-use failure::Error;
+use rusqlite;
+
+use edn;
 
 use mentat_core::{
     Attribute,
     ValueType,
 };
 
+use mentat_db;
 use mentat_query;
+use mentat_query_algebrizer;
+use mentat_query_projector;
+use mentat_query_pull;
+use mentat_sql;
 
-pub type Result<T> = std::result::Result<T, Error>;
+pub type Result<T> = std::result::Result<T, MentatError>;
 
 #[macro_export]
 macro_rules! bail {
@@ -34,6 +41,9 @@ macro_rules! bail {
 
 #[derive(Debug, Fail)]
 pub enum MentatError {
+    #[fail(display = "bad uuid {}", _0)]
+    BadUuid(String),
+
     #[fail(display = "path {} already exists", _0)]
     PathAlreadyExists(String),
 
@@ -69,4 +79,78 @@ pub enum MentatError {
 
     #[fail(display = "provided value of type {} doesn't match attribute value type {}", _0, _1)]
     ValueTypeMismatch(ValueType, ValueType),
+
+    #[fail(display = "{}", _0)]
+    IoError(#[cause] std::io::Error),
+
+    // It would be better to capture the underlying `rusqlite::Error`, but that type doesn't
+    // implement many useful traits, including `Clone`, `Eq`, and `PartialEq`.
+    #[fail(display = "SQL error: _0")]
+    RusqliteError(String),
+
+    #[fail(display = "{}", _0)]
+    EdnParseError(#[cause] edn::ParseError),
+
+    #[fail(display = "{}", _0)]
+    DbError(#[cause] mentat_db::DbError),
+
+    #[fail(display = "{}", _0)]
+    AlgebrizerError(#[cause] mentat_query_algebrizer::AlgebrizerError),
+
+    #[fail(display = "{}", _0)]
+    ProjectorError(#[cause] mentat_query_projector::ProjectorError),
+
+    #[fail(display = "{}", _0)]
+    PullError(#[cause] mentat_query_pull::PullError),
+
+    #[fail(display = "{}", _0)]
+    SQLError(#[cause] mentat_sql::SQLError),
+}
+
+impl From<std::io::Error> for MentatError {
+    fn from(error: std::io::Error) -> MentatError {
+        MentatError::IoError(error)
+    }
+}
+
+impl From<rusqlite::Error> for MentatError {
+    fn from(error: rusqlite::Error) -> MentatError {
+        MentatError::RusqliteError(error.to_string())
+    }
+}
+
+impl From<edn::ParseError> for MentatError {
+    fn from(error: edn::ParseError) -> MentatError {
+        MentatError::EdnParseError(error)
+    }
+}
+
+impl From<mentat_db::DbError> for MentatError {
+    fn from(error: mentat_db::DbError) -> MentatError {
+        MentatError::DbError(error)
+    }
+}
+
+impl From<mentat_query_algebrizer::AlgebrizerError> for MentatError {
+    fn from(error: mentat_query_algebrizer::AlgebrizerError) -> MentatError {
+        MentatError::AlgebrizerError(error)
+    }
+}
+
+impl From<mentat_query_projector::ProjectorError> for MentatError {
+    fn from(error: mentat_query_projector::ProjectorError) -> MentatError {
+        MentatError::ProjectorError(error)
+    }
+}
+
+impl From<mentat_query_pull::PullError> for MentatError {
+    fn from(error: mentat_query_pull::PullError) -> MentatError {
+        MentatError::PullError(error)
+    }
+}
+
+impl From<mentat_sql::SQLError> for MentatError {
+    fn from(error: mentat_sql::SQLError) -> MentatError {
+        MentatError::SQLError(error)
+    }
 }

src/lib.rs

@@ -104,6 +104,10 @@ macro_rules! kw {
 
 #[macro_use]
 pub mod errors;
+pub use errors::{
+    MentatError,
+    Result,
+};
 pub mod conn;
 pub mod entity_builder;
 pub mod query;

src/store.rs

@@ -234,8 +234,8 @@ impl Pullable for Store {
 }
 
 impl Syncable for Store {
-    fn sync(&mut self, server_uri: &String, user_uuid: &String) -> Result<()> {
-        let uuid = Uuid::parse_str(&user_uuid)?;
+    fn sync(&mut self, server_uri: &String, user_uuid: &String) -> ::std::result::Result<(), ::failure::Error> {
+        let uuid = Uuid::parse_str(&user_uuid).map_err(|_| MentatError::BadUuid(user_uuid.clone()))?;
         Ok(Syncer::flow(&mut self.sqlite, server_uri, &uuid)?)
     }
 }

tests/query.rs

@@ -233,7 +233,7 @@ fn test_unbound_inputs() {
     let results = q_uncached(&c, &db.schema,
                              "[:find ?i . :in ?e :where [?e :db/ident ?i]]", inputs);
 
-    match results.expect_err("expected unbound variables").downcast().expect("expected specific error") {
+    match results.expect_err("expected unbound variables") {
         MentatError::UnboundVariables(vars) => {
             assert_eq!(vars, vec!["?e".to_string()].into_iter().collect());
         },
@@ -411,8 +411,8 @@ fn test_fulltext() {
                     [?a :foo/term ?term]
                     ]"#;
     let r = conn.q_once(&mut c, query, None);
-    match r.expect_err("expected query to fail").downcast() {
-        Ok(mentat_query_algebrizer::AlgebrizerError::InvalidArgument(PlainSymbol(s), ty, i)) => {
+    match r.expect_err("expected query to fail") {
+        MentatError::AlgebrizerError(mentat_query_algebrizer::AlgebrizerError::InvalidArgument(PlainSymbol(s), ty, i)) => {
             assert_eq!(s, "fulltext");
             assert_eq!(ty, "string");
             assert_eq!(i, 2);
@@ -426,8 +426,8 @@ fn test_fulltext() {
                     [?a :foo/term ?term]
                     [(fulltext $ :foo/fts ?a) [[?x ?val]]]]"#;
     let r = conn.q_once(&mut c, query, None);
-    match r.expect_err("expected query to fail").downcast() {
-        Ok(mentat_query_algebrizer::AlgebrizerError::InvalidArgument(PlainSymbol(s), ty, i)) => {
+    match r.expect_err("expected query to fail") {
+        MentatError::AlgebrizerError(mentat_query_algebrizer::AlgebrizerError::InvalidArgument(PlainSymbol(s), ty, i)) => {
             assert_eq!(s, "fulltext");
             assert_eq!(ty, "string");
             assert_eq!(i, 2);
@@ -582,8 +582,8 @@ fn test_aggregates_type_handling() {
     // No type limits => can't do it.
     let r = store.q_once(r#"[:find (sum ?v) . :where [_ _ ?v]]"#, None);
     let all_types = ValueTypeSet::any();
-    match r.expect_err("expected query to fail").downcast() {
-        Ok(::mentat_query_projector::errors::ProjectorError::CannotApplyAggregateOperationToTypes(
+    match r.expect_err("expected query to fail") {
+        MentatError::ProjectorError(::mentat_query_projector::errors::ProjectorError::CannotApplyAggregateOperationToTypes(
             SimpleAggregationOp::Sum, types)) => {
                 assert_eq!(types, all_types);
         },
@@ -594,8 +594,8 @@ fn test_aggregates_type_handling() {
     let r = store.q_once(r#"[:find (sum ?v) .
                              :where [_ _ ?v] [(type ?v :db.type/instant)]]"#,
                          None);
-    match r.expect_err("expected query to fail").downcast() {
-        Ok(::mentat_query_projector::errors::ProjectorError::CannotApplyAggregateOperationToTypes(
+    match r.expect_err("expected query to fail") {
+        MentatError::ProjectorError(::mentat_query_projector::errors::ProjectorError::CannotApplyAggregateOperationToTypes(
             SimpleAggregationOp::Sum,
             types)) => {
                 assert_eq!(types, ValueTypeSet::of_one(ValueType::Instant));
@@ -1336,8 +1336,8 @@ fn test_aggregation_implicit_grouping() {
                                [?person :foo/play ?game]
                                [?person :foo/is-vegetarian true]
                                [?person :foo/name ?name]]"#, None);
-    match res.expect_err("expected query to fail").downcast() {
-        Ok(::mentat_query_projector::errors::ProjectorError::AmbiguousAggregates(mmc, cc)) => {
+    match res.expect_err("expected query to fail") {
+        MentatError::ProjectorError(::mentat_query_projector::errors::ProjectorError::AmbiguousAggregates(mmc, cc)) => {
             assert_eq!(mmc, 2);
             assert_eq!(cc, 1);
         },

tests/vocabulary.rs

@@ -286,8 +286,8 @@ fn test_add_vocab() {
     // Scoped borrow of `conn`.
     {
         let mut in_progress = conn.begin_transaction(&mut sqlite).expect("begun successfully");
-        match in_progress.ensure_vocabulary(&foo_v1_malformed).expect_err("expected vocabulary to fail").downcast() {
-            Ok(MentatError::ConflictingAttributeDefinitions(vocab, version, attr, theirs, ours)) => {
+        match in_progress.ensure_vocabulary(&foo_v1_malformed).expect_err("expected vocabulary to fail") {
+            MentatError::ConflictingAttributeDefinitions(vocab, version, attr, theirs, ours) => {
                 assert_eq!(vocab.as_str(), ":org.mozilla/foo");
                 assert_eq!(attr.as_str(), ":foo/baz");
                 assert_eq!(version, 1);

tools/cli/src/mentat_cli/repl.rs

@@ -11,7 +11,6 @@
 use std::io::Write;
 
 use failure::{
-    err_msg,
     Error,
 };
 
@@ -404,7 +403,8 @@ impl Repl {
         if self.path.is_empty() || path != self.path {
             let next = match encryption_key {
                 #[cfg(not(feature = "sqlcipher"))]
-                Some(_) => return Err(err_msg(".open_encrypted and .empty_encrypted require the sqlcipher Mentat feature")),
+                Some(_) => return Err(::mentat::MentatError::RusqliteError(".open_encrypted and .empty_encrypted require the sqlcipher Mentat feature".into())),
+
                 #[cfg(feature = "sqlcipher")]
                 Some(k) => {
                     if empty {