Rollup merge of #93234 - mati865:mir-transform-use-itertools, r=jackh726

rustc_mir_itertools: Avoid needless `collect` with itertools

I don't think this should have measurable perf impact (at least not on perf.rlo benchmarks), it's mostly for readability.

compiler/rustc_mir_transform/src/coverage/debug.rs

@@ -111,6 +111,7 @@
 use super::graph::{BasicCoverageBlock, BasicCoverageBlockData, CoverageGraph};
 use super::spans::CoverageSpan;
 
+use itertools::Itertools;
 use rustc_middle::mir::create_dump_file;
 use rustc_middle::mir::generic_graphviz::GraphvizWriter;
 use rustc_middle::mir::spanview::{self, SpanViewable};
@@ -739,7 +740,6 @@ pub(super) fn dump_coverage_graphviz<'tcx>(
                         )
                     }
                 })
-                .collect::<Vec<_>>()
                 .join("\n  ")
         ));
     }
@@ -768,7 +768,6 @@ fn bcb_to_string_sections<'tcx>(
                 .map(|expression| {
                     format!("Intermediate {}", debug_counters.format_counter(expression))
                 })
-                .collect::<Vec<_>>()
                 .join("\n"),
         );
     }
@@ -783,7 +782,6 @@ fn bcb_to_string_sections<'tcx>(
                         covspan.format(tcx, mir_body)
                     )
                 })
-                .collect::<Vec<_>>()
                 .join("\n"),
         );
     }
@@ -793,7 +791,6 @@ fn bcb_to_string_sections<'tcx>(
             dependency_counters
                 .iter()
                 .map(|counter| debug_counters.format_counter(counter))
-                .collect::<Vec<_>>()
                 .join("  \n"),
         ));
     }

compiler/rustc_mir_transform/src/coverage/graph.rs

@@ -1,5 +1,6 @@
 use super::Error;
 
+use itertools::Itertools;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::graph::dominators::{self, Dominators};
 use rustc_data_structures::graph::{self, GraphSuccessors, WithNumNodes, WithStartNode};
@@ -422,14 +423,7 @@ impl BasicCoverageBlockData {
     }
 
     pub fn id(&self) -> String {
-        format!(
+        format!("@{}", self.basic_blocks.iter().map(|bb| bb.index().to_string()).join(ID_SEPARATOR))
-            "@{}",
-            self.basic_blocks
-                .iter()
-                .map(|bb| bb.index().to_string())
-                .collect::<Vec<_>>()
-                .join(ID_SEPARATOR)
-        )
     }
 }
 

compiler/rustc_mir_transform/src/coverage/spans.rs

@@ -1,6 +1,7 @@
 use super::debug::term_type;
 use super::graph::{BasicCoverageBlock, BasicCoverageBlockData, CoverageGraph, START_BCB};
 
+use itertools::Itertools;
 use rustc_data_structures::graph::WithNumNodes;
 use rustc_middle::mir::spanview::source_range_no_file;
 use rustc_middle::mir::{
@@ -169,11 +170,7 @@ impl CoverageSpan {
             CoverageStatement::Statement(bb, _, index) => (bb, index),
             CoverageStatement::Terminator(bb, _) => (bb, usize::MAX),
         });
-        sorted_coverage_statements
+        sorted_coverage_statements.iter().map(|covstmt| covstmt.format(tcx, mir_body)).join("\n")
-            .iter()
-            .map(|covstmt| covstmt.format(tcx, mir_body))
-            .collect::<Vec<_>>()
-            .join("\n")
     }
 
     /// If the span is part of a macro, returns the macro name symbol.

compiler/rustc_mir_transform/src/coverage/tests.rs

@@ -31,6 +31,7 @@ use super::spans;
 
 use coverage_test_macros::let_bcb;
 
+use itertools::Itertools;
 use rustc_data_structures::graph::WithNumNodes;
 use rustc_data_structures::graph::WithSuccessors;
 use rustc_index::vec::{Idx, IndexVec};
@@ -232,11 +233,9 @@ fn print_mir_graphviz(name: &str, mir_body: &Body<'_>) {
                         mir_body
                             .successors(bb)
                             .map(|successor| { format!("    {:?} -> {:?};", bb, successor) })
-                            .collect::<Vec<_>>()
                             .join("\n")
                     )
                 })
-                .collect::<Vec<_>>()
                 .join("\n")
         );
     }
@@ -262,11 +261,9 @@ fn print_coverage_graphviz(
                         basic_coverage_blocks
                             .successors(bcb)
                             .map(|successor| { format!("    {:?} -> {:?};", bcb, successor) })
-                            .collect::<Vec<_>>()
                             .join("\n")
                     )
                 })
-                .collect::<Vec<_>>()
                 .join("\n")
         );
     }

compiler/rustc_mir_transform/src/function_item_references.rs

@@ -1,3 +1,4 @@
+use itertools::Itertools;
 use rustc_errors::Applicability;
 use rustc_hir::def_id::DefId;
 use rustc_middle::mir::visit::Visitor;
@@ -197,7 +198,7 @@ impl<'tcx> FunctionItemRefChecker<'_, 'tcx> {
         let ident = self.tcx.item_name(fn_id).to_ident_string();
         let ty_params = fn_substs.types().map(|ty| format!("{}", ty));
         let const_params = fn_substs.consts().map(|c| format!("{}", c));
-        let params = ty_params.chain(const_params).collect::<Vec<String>>().join(", ");
+        let params = ty_params.chain(const_params).join(", ");
         let num_args = fn_sig.inputs().map_bound(|inputs| inputs.len()).skip_binder();
         let variadic = if fn_sig.c_variadic() { ", ..." } else { "" };
         let ret = if fn_sig.output().skip_binder().is_unit() { "" } else { " -> _" };