#![warn(warnings)] is redundant

[epage]

From @CAD97 on April 5, 2018 13:55

The warnings warning group is a special warning group that includes the warnings which are set to the WARN level. Thus #![warn(warnings)] doesn't do anything.

The intent was probably to audit the ALLOW warnings such as unreachable_pub which should likely be enabled for new projects.

Lint checks provided by rustc:

                                         name  default  meaning
                                         ----  -------  -------
                         anonymous-parameters  allow    detects anonymous parameters
                                 box-pointers  allow    use of owned (Box type) heap memory
                      elided-lifetime-in-path  allow    hidden lifetime parameters are deprecated, try `Foo<'_>`
                 missing-copy-implementations  allow    detects potentially-forgotten implementations of `Copy`
                missing-debug-implementations  allow    detects missing implementations of fmt::Debug
                                 missing-docs  allow    detects missing documentation for public members
                          single-use-lifetime  allow    detects single use lifetimes
                                trivial-casts  allow    detects trivial casts which could be removed
                        trivial-numeric-casts  allow    detects trivial casts of numeric types which could be removed
                              unreachable-pub  allow    `pub` items not reachable from crate root
                                  unsafe-code  allow    usage of `unsafe` code
                            unstable-features  allow    enabling unstable features (deprecated. do not use)
                         unused-extern-crates  allow    extern crates that are never used
                         unused-import-braces  allow    unnecessary braces around an imported item
                        unused-qualifications  allow    detects unnecessarily qualified names
                               unused-results  allow    unused result of an expression in a statement
                     variant-size-differences  allow    detects enums with widely varying variant sizes
                                               [snip]


Lint groups provided by rustc:

                   name  sub-lints
                   ----  ---------
               warnings  all lints that are set to issue warnings
              bad-style  non-camel-case-types, non-snake-case, non-upper-case-globals
    future-incompatible  private-in-public, pub-use-of-private-extern-crate, patterns-in-fns-without-body, safe-extern-statics, invalid-type-param-default, legacy-directory-ownership, legacy-imports, legacy-constructor-visibility, resolve-trait-on-defaulted-unit, missing-fragment-specifier, illegal-floating-point-literal-pattern, anonymous-parameters, parenthesized-params-in-types-and-modules, late-bound-lifetime-arguments, safe-packed-borrows, incoherent-fundamental-impls, coerce-never, tyvar-behind-raw-pointer
                 unused  unused-imports, unused-variables, unused-assignments, dead-code, unused-mut, unreachable-code, unreachable-patterns, unused-must-use, unused-unsafe, path-statements, unused-attributes, unused-macros, unused-allocation, unused-doc-comment, unused-extern-crates, unused-features, unused-parens

We probably want to deny unsafe-code and warn for missing-debug-implementations, missing-docs, and unreachable-pub.

Copied from original issue: crate-ci/example-warn#4