Upgrade minimal supported version of Rust to 1.47.

We have so far maintained compatibility with Rust 1.41+.  Newer versions
have more and more features that we'd like to use, as well as some that
break backwards compatibility.  We therefore upgrade our Rust dependency
to 1.47.

Some earlier versions might still work, but 1.47.0 is going to be the
earliest "officially" supported one.

README.md

@@ -1,7 +1,7 @@
 [![License: MIT](https://img.shields.io/badge/License-MIT-green.svg)](https://opensource.org/licenses/MIT)
 [![Build Status](https://travis-ci.com/vmware/differential-datalog.svg?branch=master)](https://travis-ci.com/vmware/differential-datalog)
 [![pipeline status](https://gitlab.com/ddlog/differential-datalog/badges/master/pipeline.svg)](https://gitlab.com/ddlog/differential-datalog/commits/master)
-[![rustc](https://img.shields.io/badge/rustc-1.41+-blue.svg)](https://blog.rust-lang.org/2020/03/12/Rust-1.42.html)
+[![rustc](https://img.shields.io/badge/rustc-1.47+-blue.svg)](https://blog.rust-lang.org/2020/10/08/Rust-1.47.html)
 [![Gitter chat](https://badges.gitter.im/vmware/differential-datalog.png)](https://gitter.im/vmware/differential-datalog)
 
 # Differential Datalog (DDlog)
@@ -96,7 +96,7 @@ You are now ready to [start coding in DDlog](doc/tutorial/tutorial.md).
   ```
   wget -qO- https://get.haskellstack.org/ | sh
   ```
-- Rust toolchain v1.41 or later:
+- Rust toolchain v1.47 or later:
   ```
   curl https://sh.rustup.rs -sSf | sh
   . $HOME/.cargo/env

rust/template/differential_datalog/src/lib.rs

@@ -1,13 +1,8 @@
 #![allow(
-    clippy::unknown_clippy_lints,
     clippy::get_unwrap,
     clippy::missing_safety_doc,
     clippy::type_complexity,
-    clippy::match_like_matches_macro,
-    // match_like_matches_macro not supported in older versions of clippy
-    clippy::unknown_clippy_lints,
-    // required because of a bug in older clippy (1.41).
-    clippy::useless_let_if_seq
+    clippy::match_like_matches_macro
 )]
 
 mod callback;

rust/template/differential_datalog_test/lib.rs

@@ -17,9 +17,7 @@
     clippy::cmp_owned,
     clippy::nonminimal_bool,
     clippy::toplevel_ref_arg,
-    clippy::trivially_copy_pass_by_ref,
-    // blocks_in_if_conditions is unknown to older version of clippy.
-    clippy::unknown_clippy_lints
+    clippy::trivially_copy_pass_by_ref
 )]
 
 use std::borrow::Cow;

rust/template/src/lib.rs

@@ -9,7 +9,6 @@
     overflowing_literals,
     unreachable_patterns,
     unused_variables,
-    clippy::unknown_clippy_lints,
     clippy::missing_safety_doc,
     clippy::toplevel_ref_arg,
     clippy::double_parens,

rust/template/src/main.rs

@@ -2,13 +2,7 @@
 //! CLI), parsing them with cmd_parser crate, executing commands, and tracking database state in a
 //! map.
 
-#![allow(
-    dead_code,
-    non_snake_case,
-    clippy::match_like_matches_macro,
-    //match_like_matches_macro not supported in older versions of clippy
-    clippy::unknown_clippy_lints
-)]
+#![allow(dead_code, non_snake_case, clippy::match_like_matches_macro)]
 
 use std::convert::TryFrom;
 use std::io::stdout;

rust/template/types/lib.rs

@@ -10,7 +10,6 @@
     overflowing_literals,
     unreachable_patterns,
     unused_variables,
-    clippy::unknown_clippy_lints,
     clippy::missing_safety_doc,
     clippy::match_single_binding,
     clippy::ptr_arg,

tools/Dockerfile

@@ -36,7 +36,7 @@ ENV PATH=/root/.local/bin:/root/.cargo/bin:$PATH
 ENV CLASSPATH=$CLASSPATH:/flatbuffers/java
 
 # Install Rust
-RUN curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain 1.41.1 -y
+RUN curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain 1.47.0 -y
 RUN rustup component add rustfmt
 RUN rustup component add clippy