rollup merge of #20289: nick29581/shadowing

r? eddyb

diff --cc src/libcollections/slice.rs
Simple merge

diff --cc src/libcollections/str.rs
Simple merge

diff --cc src/librustc_resolve/lib.rs
Simple merge

diff --cc src/librustc_trans/trans/base.rs
Simple merge

diff --cc src/librustc_trans/trans/common.rs
Simple merge

diff --cc src/libstd/io/mem.rs
Simple merge

diff --cc src/libstd/io/mod.rs
Simple merge

diff --cc src/libstd/io/net/udp.rs
Simple merge

diff --cc src/libstd/io/util.rs
Simple merge