cmd/compile: very long names for simple generic usage

[rsc]

Go version

go1.23.5, go1.24rc2

Output of go env in your module/workspace:

n/a

What did you do?

Build a program using a few TransientSlice[Value].
Profile it, showing hot symbols.
Run nm to see symbols.

git clone https://github.com/rsc/ivy
cd ivy
git fetch pprofbug # tag I created
go build
go tool nm ./ivy | grep Append
./ivy -profile=x.prof testdata/copy.ivy
go tool pprof ./ivy
top10

What did you see happen?

Unexpectedly long symbol names, like in the comically large and unreadable boxes in this profile:

Or in this nm output:

% go tool nm ivy | grep Append
1000cbb10 T math/big.(*Float).Append
100131f60 T robpike.io/ivy/internal/persist.(*TransientSlice[go.shape.interface { Eval(robpike.io/ivy/value.Context) robpike.io/ivy/value.Value; Inner() robpike.io/ivy/value.Value; ProgString() string; Rank() int; Sprint(*robpike.io/ivy/config.Config) string; String() string; robpike.io/ivy/value.shrink() robpike.io/ivy/value.Value; robpike.io/ivy/value.toType(string, *robpike.io/ivy/config.Config, robpike.io/ivy/value.valueType) robpike.io/ivy/value.Value }]).Append
1000837d0 T strconv.AppendInt
1000944e0 T time.Time.AppendFormat
% 

What did you expect to see?

Reasonably short symbol names, and normal-sized pprof boxes.

[rsc]

Note that the actual code uses an interface, not that long literal.

% grep TransientSlice value/*.go
value/vector.go:	t *persist.TransientSlice[Value]
value/vector.go:	t := new(persist.TransientSlice[Value])
% 

Since the Value interface mentions Value itself, basically no one is ever going to write that literal accidentally, so there is arguably no reason to expand Value into the long literal. In the case where the argument is a named interface that mentions itself, or a named interface with more than N methods, it seems like it would be better to just use the interface name, so that these would show up in the code as

robpike.io/ivy/internal/persist.(*TransientSlice[go.shape.robpike.io/ivy/value.Value]).Append

That's still longer than one would hope, but far shorter than the current symbol names.

[rsc]

Another example of the long names showing up in an unwanted place: race detector reports.

WARNING: DATA RACE
Read at 0x00c000788268 by goroutine 4853:
  robpike.io/ivy/internal/persist.(*TransientSlice[go.shape.interface { Eval(robpike.io/ivy/value.Context) robpike.io/ivy/value.Value; Inner() robpike.io/ivy/value.Value; ProgString() string; Rank() int; Sprint(*robpike.io/ivy/config.Config) string; String() string; robpike.io/ivy/value.shrink() robpike.io/ivy/value.Value; robpike.io/ivy/value.toType(string, *robpike.io/ivy/config.Config, robpike.io/ivy/value.valueType) robpike.io/ivy/value.Value }]).wnode()
      /Users/rsc/src/robpike.io/ivy/internal/persist/slice.go:251 +0x90
  robpike.io/ivy/internal/persist.(*TransientSlice[go.shape.interface { Eval(robpike.io/ivy/value.Context) robpike.io/ivy/value.Value; Inner() robpike.io/ivy/value.Value; ProgString() string; Rank() int; Sprint(*robpike.io/ivy/config.Config) string; String() string; robpike.io/ivy/value.shrink() robpike.io/ivy/value.Value; robpike.io/ivy/value.toType(string, *robpike.io/ivy/config.Config, robpike.io/ivy/value.valueType) robpike.io/ivy/value.Value }]).Set()
      /Users/rsc/src/robpike.io/ivy/internal/persist/slice.go:322 +0x2d4
  robpike.io/ivy/value.(*vectorEditor).Set()
      /Users/rsc/src/robpike.io/ivy/value/vector.go:74 +0x368
  robpike.io/ivy/value.IndexAssign.func2()
      /Users/rsc/src/robpike.io/ivy/value/index.go:353 +0x2e4
  robpike.io/ivy/value.pfor.func1()
      /Users/rsc/src/robpike.io/ivy/value/eval.go:223 +0x90

Previous write at 0x00c000788268 by goroutine 4852:
  robpike.io/ivy/internal/persist.(*TransientSlice[go.shape.interface { Eval(robpike.io/ivy/value.Context) robpike.io/ivy/value.Value; Inner() robpike.io/ivy/value.Value; ProgString() string; Rank() int; Sprint(*robpike.io/ivy/config.Config) string; String() string; robpike.io/ivy/value.shrink() robpike.io/ivy/value.Value; robpike.io/ivy/value.toType(string, *robpike.io/ivy/config.Config, robpike.io/ivy/value.valueType) robpike.io/ivy/value.Value }]).init()
      /Users/rsc/src/robpike.io/ivy/internal/persist/slice.go:213 +0x138
  robpike.io/ivy/internal/persist.(*TransientSlice[go.shape.interface { Eval(robpike.io/ivy/value.Context) robpike.io/ivy/value.Value; Inner() robpike.io/ivy/value.Value; ProgString() string; Rank() int; Sprint(*robpike.io/ivy/config.Config) string; String() string; robpike.io/ivy/value.shrink() robpike.io/ivy/value.Value; robpike.io/ivy/value.toType(string, *robpike.io/ivy/config.Config, robpike.io/ivy/value.valueType) robpike.io/ivy/value.Value }]).wnode()
      /Users/rsc/src/robpike.io/ivy/internal/persist/slice.go:252 +0xf0
  robpike.io/ivy/internal/persist.(*TransientSlice[go.shape.interface { Eval(robpike.io/ivy/value.Context) robpike.io/ivy/value.Value; Inner() robpike.io/ivy/value.Value; ProgString() string; Rank() int; Sprint(*robpike.io/ivy/config.Config) string; String() string; robpike.io/ivy/value.shrink() robpike.io/ivy/value.Value; robpike.io/ivy/value.toType(string, *robpike.io/ivy/config.Config, robpike.io/ivy/value.valueType) robpike.io/ivy/value.Value }]).Set()
      /Users/rsc/src/robpike.io/ivy/internal/persist/slice.go:322 +0x2d4
  robpike.io/ivy/value.(*vectorEditor).Set()
      /Users/rsc/src/robpike.io/ivy/value/vector.go:74 +0x368
  robpike.io/ivy/value.IndexAssign.func2()
      /Users/rsc/src/robpike.io/ivy/value/index.go:353 +0x2e4
  robpike.io/ivy/value.pfor.func1()
      /Users/rsc/src/robpike.io/ivy/value/eval.go:223 +0x90
...

[mknyszek]

Related to #60324.

[seankhliao]

also related? #50438