Add a rudimentary SQL builder, based on parts of Diesel. (#273) r=nalexander

https://github.com/diesel-rs/diesel/

Cargo.toml

@@ -35,6 +35,9 @@ path = "parser-utils"
 [dependencies.mentat_core]
 path = "core"
 
+[dependencies.mentat_sql]
+path = "sql"
+
 [dependencies.mentat_db]
 path = "db"
 

sql/Cargo.toml

@@ -0,0 +1,3 @@
+[package]
+name = "mentat_sql"
+version = "0.0.1"

sql/README.md

@@ -0,0 +1,7 @@
+This is a tiny SQL query builder.
+
+The majority of this code was distilled from QueryBuilder in Diesel:
+
+https://github.com/diesel-rs/diesel/
+
+used under the Apache 2.0 license.

sql/src/lib.rs

@@ -0,0 +1,79 @@
+// Copyright 2016 Mozilla
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+use std::error::Error;
+
+pub type BuildQueryError = Box<Error + Send + Sync>;
+pub type BuildQueryResult = Result<(), BuildQueryError>;
+
+/// Gratefully based on Diesel's QueryBuilder trait:
+/// https://github.com/diesel-rs/diesel/blob/4885f61b8205f7f3c2cfa03837ed6714831abe6b/diesel/src/query_builder/mod.rs#L56
+pub trait QueryBuilder {
+    fn push_sql(&mut self, sql: &str);
+    fn push_identifier(&mut self, identifier: &str) -> BuildQueryResult;
+    fn push_bind_param(&mut self);
+    fn finish(self) -> String;
+}
+
+pub trait QueryFragment {
+    fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult;
+}
+
+impl QueryFragment for Box<QueryFragment> {
+    fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
+        QueryFragment::push_sql(&**self, out)
+    }
+}
+
+impl<'a> QueryFragment for &'a QueryFragment {
+    fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
+        QueryFragment::push_sql(&**self, out)
+    }
+}
+
+impl QueryFragment for () {
+    fn push_sql(&self, _out: &mut QueryBuilder) -> BuildQueryResult {
+        Ok(())
+    }
+}
+
+/// A QueryBuilder that implements SQLite's specific escaping rules.
+pub struct SQLiteQueryBuilder {
+    pub sql: String,
+}
+
+impl SQLiteQueryBuilder {
+    pub fn new() -> Self {
+        SQLiteQueryBuilder {
+            sql: String::new(),
+        }
+    }
+}
+
+impl QueryBuilder for SQLiteQueryBuilder {
+    fn push_sql(&mut self, sql: &str) {
+        self.sql.push_str(sql);
+    }
+
+    fn push_identifier(&mut self, identifier: &str) -> BuildQueryResult {
+        self.push_sql("`");
+        self.push_sql(&identifier.replace("`", "``"));
+        self.push_sql("`");
+        Ok(())
+    }
+
+    fn push_bind_param(&mut self) {
+        self.push_sql("?");
+    }
+
+    fn finish(self) -> String {
+        self.sql
+    }
+}