use vec![] macro to create Vector with first item inside instead of pushing to an empty vec![]

slightly reduces code bloat

Author: matthiaskrgr

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -2189,8 +2189,7 @@ impl<'a> State<'a> {
             Options(InlineAsmOptions),
         }
 
-        let mut args = vec![];
-        args.push(AsmArg::Template(InlineAsmTemplatePiece::to_string(&asm.template)));
+        let mut args = vec![AsmArg::Template(InlineAsmTemplatePiece::to_string(&asm.template))];
         args.extend(asm.operands.iter().map(|(o, _)| AsmArg::Operand(o)));
         if !asm.options.is_empty() {
             args.push(AsmArg::Options(asm.options));

compiler/rustc_hir_pretty/src/lib.rs

@@ -1356,8 +1356,8 @@ impl<'a> State<'a> {
             Options(ast::InlineAsmOptions),
         }
 
-        let mut args = vec![];
-        args.push(AsmArg::Template(ast::InlineAsmTemplatePiece::to_string(&asm.template)));
+        let mut args =
+            vec![AsmArg::Template(ast::InlineAsmTemplatePiece::to_string(&asm.template))];
         args.extend(asm.operands.iter().map(|(o, _)| AsmArg::Operand(o)));
         if !asm.options.is_empty() {
             args.push(AsmArg::Options(asm.options));

compiler/rustc_mir/src/transform/coverage/graph.rs

@@ -526,8 +526,8 @@ impl TraverseCoverageGraphWithLoops {
     pub fn new(basic_coverage_blocks: &CoverageGraph) -> Self {
         let start_bcb = basic_coverage_blocks.start_node();
         let backedges = find_loop_backedges(basic_coverage_blocks);
-        let mut context_stack = Vec::new();
-        context_stack.push(TraversalContext { loop_backedges: None, worklist: vec![start_bcb] });
+        let context_stack =
+            vec![TraversalContext { loop_backedges: None, worklist: vec![start_bcb] }];
         // `context_stack` starts with a `TraversalContext` for the main function context (beginning
         // with the `start` BasicCoverageBlock of the function). New worklists are pushed to the top
         // of the stack as loops are entered, and popped off of the stack when a loop's worklist is

compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs

@@ -124,11 +124,10 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             self.impl_similar_to(trait_ref, obligation).unwrap_or_else(|| trait_ref.def_id());
         let trait_ref = trait_ref.skip_binder();
 
-        let mut flags = vec![];
-        flags.push((
+        let mut flags = vec![(
             sym::ItemContext,
             self.describe_enclosure(obligation.cause.body_id).map(|s| s.to_owned()),
-        ));
+        )];
 
         match obligation.cause.code {
             ObligationCauseCode::BuiltinDerivedObligation(..)