Add optional description to @time and new @showtime macro

NEWS.md

@@ -22,6 +22,9 @@ Language changes
 * Newly created Task objects (`@spawn`, `@async`, etc.) now adopt the world-age for methods from their parent
   Task upon creation, instead of using the global latest world at start. This is done to enable inference to
   eventually optimize these calls. Places that wish for the old behavior may use `Base.invokelatest`. ([#41449])
+* `@time` and `@timev` now take an optional description to allow annotating the source of time reports.
+  i.e. `@time "Evaluating foo" foo()` ([#42431])
+* New `@showtime` macro to show both the line being evaluated and the `@time` report ([#42431])
 
 Compiler/Runtime improvements
 -----------------------------

base/exports.jl

@@ -992,6 +992,7 @@ export
 
     # profiling
     @time,
+    @showtime,
     @timed,
     @timev,
     @elapsed,

base/timing.jl

@@ -175,25 +175,31 @@ macro __tryfinally(ex, fin)
 end
 
 """
-    @time
+    @time expr
+    @time "description" expr
 
 A macro to execute an expression, printing the time it took to execute, the number of
 allocations, and the total number of bytes its execution caused to be allocated, before
 returning the value of the expression. Any time spent garbage collecting (gc) or
 compiling is shown as a percentage.
 
+Optionally provide a description string to print before the time report.
+
 In some cases the system will look inside the `@time` expression and compile some of the
 called code before execution of the top-level expression begins. When that happens, some
 compilation time will not be counted. To include this time you can run `@time @eval ...`.
 
-See also [`@timev`](@ref), [`@timed`](@ref), [`@elapsed`](@ref), and
+See also [`@showtime`](@ref), [`@timev`](@ref), [`@timed`](@ref), [`@elapsed`](@ref), and
 [`@allocated`](@ref).
 
 !!! note
     For more serious benchmarking, consider the `@btime` macro from the BenchmarkTools.jl
     package which among other things evaluates the function multiple times in order to
     reduce noise.
 
+!!! compat "Julia 1.8"
+    The option to add a description was introduced in Julia 1.8.
+
 ```julia-repl
 julia> x = rand(10,10);
 
@@ -209,9 +215,24 @@ julia> @time begin
        end
   0.301395 seconds (8 allocations: 336 bytes)
 2
+
+julia> @time "A one second sleep" sleep(1)
+A one second sleep ->  1.005750 seconds (5 allocations: 144 bytes)
+
+julia> for loop in 1:3
+            @time loop sleep(1)
+        end
+1 ->  1.006760 seconds (5 allocations: 144 bytes)
+2 ->  1.001263 seconds (5 allocations: 144 bytes)
+3 ->  1.003676 seconds (5 allocations: 144 bytes)
 ```
 """
 macro time(ex)
+    quote
+        @time nothing $(esc(ex))
+    end
+end
+macro time(msg, ex)
     quote
         Experimental.@force_compile
         local stats = gc_num()
@@ -222,18 +243,46 @@ macro time(ex)
             compile_elapsedtime = cumulative_compile_time_ns_after() - compile_elapsedtime)
         )
         local diff = GC_Diff(gc_num(), stats)
+        isnothing($(esc(msg))) || print($(esc(msg)), " ->")
         time_print(elapsedtime, diff.allocd, diff.total_time, gc_alloc_count(diff), compile_elapsedtime, true)
         val
     end
 end
 
 """
-    @timev
+    @showtime expr
+
+Like `@time` but also prints the expression being evaluated for reference.
+
+!!! compat "Julia 1.8"
+    This macro was added in Julia 1.8.
+
+See also [`@time`](@ref).
+
+```julia-repl
+julia> @showtime sleep(1)
+sleep(1) ->  1.002164 seconds (4 allocations: 128 bytes)
+```
+"""
+macro showtime(ex)
+    quote
+        @time $(sprint(show_unquoted,ex)) $(esc(ex))
+    end
+end
+
+"""
+    @timev expr
+    @timev "description" expr
 
 This is a verbose version of the `@time` macro. It first prints the same information as
 `@time`, then any non-zero memory allocation counters, and then returns the value of the
 expression.
 
+Optionally provide a description string to print before the time report.
+
+!!! compat "Julia 1.8"
+    The option to add a description was introduced in Julia 1.8.
+
 See also [`@time`](@ref), [`@timed`](@ref), [`@elapsed`](@ref), and
 [`@allocated`](@ref).
 
@@ -259,6 +308,11 @@ pool allocs:       1
 ```
 """
 macro timev(ex)
+    quote
+        @timev nothing $(esc(ex))
+    end
+end
+macro timev(msg, ex)
     quote
         Experimental.@force_compile
         local stats = gc_num()
@@ -269,6 +323,7 @@ macro timev(ex)
             compile_elapsedtime = cumulative_compile_time_ns_after() - compile_elapsedtime)
         )
         local diff = GC_Diff(gc_num(), stats)
+        isnothing($(esc(msg))) || print($(esc(msg)), " ->")
         timev_print(elapsedtime, diff, compile_elapsedtime)
         val
     end

doc/src/base/base.md

@@ -320,6 +320,7 @@ Base.Libc.getpid
 Base.Libc.time()
 Base.time_ns
 Base.@time
+Base.@showtime
 Base.@timev
 Base.@timed
 Base.@elapsed

test/misc.jl

@@ -242,6 +242,35 @@ v11801, t11801 = @timed sin(1)
 
 @test names(@__MODULE__, all = true) == names_before_timing
 
+# Accepted @time argument formats
+@test @time true
+@test @time "message" true
+let msg = "message"
+    @test @time msg true
+end
+let foo() = "message"
+    @test @time foo() true
+end
+
+# Accepted @timev argument formats
+@test @timev true
+@test @timev "message" true
+let msg = "message"
+    @test @timev msg true
+end
+let foo() = "message"
+    @test @timev foo() true
+end
+
+# @showtime
+@test @showtime true
+let foo() = true
+    @test @showtime foo()
+end
+let foo() = false
+    @test (@showtime foo()) == false
+end
+
 # PR #39133, ensure that @time evaluates in the same scope
 function time_macro_scope()
     try # try/throw/catch bypasses printing