Make clippy happy + a few more cleanups

[nyurik]

Following up from #283

• Address all remaining clippy issues
• Switch assert!(a==b) to assert_eq!(a, b)
• MAX instead of max_value()
• A few doc string changes (make docs look nicer)
• Collapse Ok(a) | Ok(b) into Ok(a | b)

expand original clippy messages

warning: this seems like a manual implementation of the non-exhaustive pattern
--> src/mem.rs:46:1
|
46 | pub enum FlushCompress {
| ^---------------------
| |
| _help: add the attribute: #[non_exhaustive] pub enum FlushCompress
| |
47 | | /// A typical parameter for passing to compression/decompression functions,
48 | | /// this indicates that the underlying stream to decide how much data to
49 | | /// accumulate before producing output in order to maximize compression.
... |
85 | | Nonexhaustive,
86 | | }
| |^
|
= note: #[warn(clippy::manual_non_exhaustive)] on by default
help: remove this variant
--> src/mem.rs:85:5
|
85 | _Nonexhaustive,
| ^^^^^^^^^^^^^^
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_non_exhaustive

warning: this seems like a manual implementation of the non-exhaustive pattern
--> src/mem.rs:91:1
|
91 | pub enum FlushDecompress {
| ^-----------------------
| |
| _help: add the attribute: #[non_exhaustive] pub enum FlushDecompress
| |
92 | | /// A typical parameter for passing to compression/decompression functions,
93 | | /// this indicates that the underlying stream to decide how much data to
94 | | /// accumulate before producing output in order to maximize compression.
... |
113 | | Nonexhaustive,
114 | | }
| |^
|
help: remove this variant
--> src/mem.rs:113:5
|
113 | _Nonexhaustive,
| ^^^^^^^^^^^^^^
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#manual_non_exhaustive

warning: the operation is ineffective. Consider reducing it to (header[4] as u32)
--> src/gz/bufread.rs:58:39
|
58 | r.part.header.mtime = ((header[4] as u32) << 0)
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: #[warn(clippy::identity_op)] on by default
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: ref on an entire let pattern is discouraged, take a reference with & instead
--> src/gz/bufread.rs:197:13
|
197 | let ref arr = [
| ^^^^^^^
|
= note: #[warn(clippy::toplevel_ref_arg)] on by default
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#toplevel_ref_arg
help: try
|
197 ~ let arr = &[
198 + (crc.sum() >> 0) as u8,
199 + (crc.sum() >> 8) as u8,
200 + (crc.sum() >> 16) as u8,
201 + (crc.sum() >> 24) as u8,
202 + (crc.amount() >> 0) as u8,
...

warning: the operation is ineffective. Consider reducing it to crc.sum()
--> src/gz/bufread.rs:198:13
|
198 | (crc.sum() >> 0) as u8,
| ^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to crc.amount()
--> src/gz/bufread.rs:202:13
|
202 | (crc.amount() >> 0) as u8,
| ^^^^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to (buf[0] as u32)
--> src/gz/bufread.rs:233:15
|
233 | let crc = ((buf[0] as u32) << 0)
| ^^^^^^^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to (buf[4] as u32)
--> src/gz/bufread.rs:237:15
|
237 | let amt = ((buf[4] as u32) << 0)
| ^^^^^^^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to sum
--> src/gz/write.rs:102:17
|
102 | (sum >> 0) as u8,
| ^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to amt
--> src/gz/write.rs:106:17
|
106 | (amt >> 0) as u8,
| ^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to (self.crc_bytes[0] as u32)
--> src/gz/write.rs:307:19
|
307 | let crc = ((self.crc_bytes[0] as u32) << 0)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to (self.crc_bytes[4] as u32)
--> src/gz/write.rs:311:19
|
311 | let amt = ((self.crc_bytes[4] as u32) << 0)
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: the operation is ineffective. Consider reducing it to v.len()
--> src/gz/mod.rs:215:25
|
215 | header.push((v.len() >> 0) as u8);
| ^^^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: you are using an explicit closure for copying elements
--> src/gz/mod.rs:221:27
|
221 | header.extend(filename.as_bytes_with_nul().iter().map(|x| *x));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider calling the dedicated copied method: filename.as_bytes_with_nul().iter().copied()
|
= note: #[warn(clippy::map_clone)] on by default
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_clone

warning: you are using an explicit closure for copying elements
--> src/gz/mod.rs:225:27
|
225 | header.extend(comment.as_bytes_with_nul().iter().map(|x| *x));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider calling the dedicated copied method: comment.as_bytes_with_nul().iter().copied()
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_clone

warning: the operation is ineffective. Consider reducing it to mtime
--> src/gz/mod.rs:231:21
|
231 | header[4] = (mtime >> 0) as u8;
| ^^^^^^^^^^^^
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

warning: use of offset with a usize casted to an isize
--> src/mem.rs:365:27
|
365 | let ptr = output.as_mut_ptr().offset(len as isize);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: output.as_mut_ptr().add(len)
|
= note: #[warn(clippy::ptr_offset_with_cast)] on by default
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_offset_with_cast

warning: use of offset with a usize casted to an isize
--> src/mem.rs:506:27
|
506 | let ptr = output.as_mut_ptr().offset(len as isize);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: output.as_mut_ptr().add(len)
|
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_offset_with_cast

warning: flate2 (lib) generated 18 warnings
Finished dev [unoptimized + debuginfo] target(s) in 0.02s

[alexcrichton]

Sorry this is as far as I got but I personally really do not like reviewing clippy changes, so I'm going to stop here.

[JohnTitor]

@nyurik Friendly-ping, could you check the above review comments?

[nyurik]

@JohnTitor thanks for the ping! I addressed the feedback, and also added a few minor ones

[nyurik]

Quick question: in write!(f, "deflate compression error: {}", msg) -- which Rust version does flate2-rs target? Can inline format args be used here?

[JohnTitor]

Quick question: in write!(f, "deflate compression error: {}", msg) -- which Rust version does flate2-rs target? Can inline format args be used here?

Let's leave them as-is for now.
According to #207 (comment), MSRV is N-1 stable. The maintainership has, however, been changed recently and I'd like to declare it explicitly first.

[JohnTitor]

Thanks!