Minimize pub usage in source_map.rs.

Most notably, this commit changes the `pub use crate::*;` in that file
to `use crate::*;`. This requires a lot of `use` items in other crates
to be adjusted, because everything defined within `rustc_span::*` was
also available via `rustc_span::source_map::*`, which is bizarre.

The commit also removes `SourceMap::span_to_relative_line_string`, which
is unused.

compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs

@@ -5,7 +5,7 @@ use crate::traits::{Normalized, ObligationCause, ObligationCtxt};
 use rustc_data_structures::fx::FxHashSet;
 use rustc_middle::traits::query::{DropckConstraint, DropckOutlivesResult};
 use rustc_middle::ty::{self, EarlyBinder, ParamEnvAnd, Ty, TyCtxt};
-use rustc_span::source_map::{Span, DUMMY_SP};
+use rustc_span::{Span, DUMMY_SP};
 
 /// This returns true if the type `ty` is "trivial" for
 /// dropck-outlives -- that is, if it doesn't require any types to

compiler/rustc_trait_selection/src/traits/query/type_op/custom.rs

@@ -6,8 +6,7 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_infer::infer::region_constraints::RegionConstraintData;
 use rustc_middle::traits::query::NoSolution;
 use rustc_middle::ty::{TyCtxt, TypeFoldable};
-use rustc_span::source_map::DUMMY_SP;
-use rustc_span::Span;
+use rustc_span::{Span, DUMMY_SP};
 
 use std::fmt;
 

compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs

@@ -10,7 +10,7 @@ use rustc_middle::infer::canonical::CanonicalQueryResponse;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::{self, ParamEnvAnd, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::def_id::CRATE_DEF_ID;
-use rustc_span::source_map::DUMMY_SP;
+use rustc_span::DUMMY_SP;
 use smallvec::{smallvec, SmallVec};
 
 #[derive(Copy, Clone, Debug, HashStable, TypeFoldable, TypeVisitable)]