trace: add script to generate experimental API from a Go checkout

For golang/go#62627.

Change-Id: I48080a9e55ea3e5979a51f303a0c99de9218fd13
Reviewed-on: https://go-review.googlesource.com/c/exp/+/546737
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>

trace/gen.bash

@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+# Copyright 2023 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+# This script copies this directory to golang.org/x/exp/trace.
+# Just point it at a Go commit or a local Go checkout.
+
+set -e
+
+if [ "$#" -ne 1 ]; then
+	echo 'gen.bash expects one argument: a go.googlesource.com/go commit hash to generate the package from or a path to a Go checkout'
+	exit 1
+fi
+
+# Determine the source.
+if [ -d $1 ]; then
+	echo "assuming Go checkout at $1..."
+
+	# Select the Go checkout.
+	GODIR=$1
+else
+	echo "using $1 as a commit hash..."
+
+	# Check out Go.
+	TMP=$(mktemp -d)
+	git -C $TMP clone https://go.googlesource.com/go
+	git -C $TMP/go checkout $1
+	GODIR=$TMP/go
+fi
+
+# Define src and dst.
+SRC=$GODIR/src/internal/trace/v2
+DST=$(dirname $0)
+
+# Copy.
+cp -r $SRC/* $DST
+rm $DST/mkexp.bash
+
+# Remove the trace_test.go file and the testprogs it invokes.
+# This really tests the tracer, it's not necessary to it bring along
+# The trace tests are also problematic because they fail to run on
+# Go versions before tip. The testprog directory is problematic because
+# of //go:build ignore, so we'd have to complicate the logic below to
+# support it.
+rm $DST/trace_test.go
+rm -r $DST/testdata/testprog
+
+# Remove mktests.go because its a //go:build ignore file, so it would
+# complicate the logic below. This codebase isn't the source of truth
+# anyway.
+rm $DST/testdata/mktests.go
+
+# Make some packages internal.
+mv $DST/raw $DST/internal/raw
+mv $DST/event $DST/internal/event
+mv $DST/version $DST/internal/version
+mv $DST/testtrace $DST/internal/testtrace
+
+# Move the debug commands out of testdata.
+mv $DST/testdata/cmd $DST/cmd
+
+# Fix up import paths.
+find $DST -name '*.go' | xargs -- sed -i 's/internal\/trace\/v2/golang.org\/x\/exp\/trace/'
+find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/raw/golang.org\/x\/exp\/trace\/internal\/raw/'
+find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/event/golang.org\/x\/exp\/trace\/internal\/event/'
+find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/event\/go122/golang.org\/x\/exp\/trace\/internal\/event\/go122/'
+find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/version/golang.org\/x\/exp\/trace\/internal\/version/'
+find $DST -name '*.go' | xargs -- sed -i 's/golang.org\/x\/exp\/trace\/testtrace/golang.org\/x\/exp\/trace\/internal\/testtrace/'
+find $DST -name '*.go' | xargs -- sed -i 's/internal\/txtar/golang.org\/x\/tools\/txtar/'
+
+# Add build tag for Go 1.21 and generated code comment.
+find $DST -name '*.go' | xargs -- sed -i '/LICENSE file./a \
+\
+// Code generated by "gen.bash" from internal/trace/v2; DO NOT EDIT.\n\n//go:build go1.21'
+
+# Format the files.
+find $DST -name '*.go' | xargs -- gofmt -w -s