tools/trim: add tracer

Change-Id: I99af9bfdb5448578cc4fdf0aacee9305a00f4851
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/8701
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>

tools/trim/debug.go

@@ -0,0 +1,50 @@
+// Copyright 2021 CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package trim
+
+import (
+	"fmt"
+	"strings"
+
+	"cuelang.org/go/internal/core/adt"
+)
+
+func (t *trimmer) trace(v *adt.Vertex) (*trimmer, *adt.Vertex) {
+	if t.debug {
+		t.indent++
+		fmt.Fprintf(t.w, "%s%s {\n",
+			strings.Repeat("..", t.indent),
+			v.Label.SelectorString(t.ctx))
+	}
+	return t, v
+}
+
+func un(t *trimmer, v *adt.Vertex) {
+	if !t.debug {
+		return
+	}
+	fmt.Fprintf(t.w, "%s}\n",
+		strings.Repeat("..", t.indent))
+	t.indent--
+}
+
+func (t *trimmer) logf(format string, args ...interface{}) {
+	if !t.debug {
+		return
+	}
+	fmt.Fprint(t.w, strings.Repeat("..", t.indent+1))
+	fmt.Fprintf(t.w, format, args...)
+	fmt.Fprintln(t.w)
+}

tools/trim/trim.go

@@ -50,11 +50,15 @@
 package trim
 
 import (
+	"io"
+	"os"
+
 	"cuelang.org/go/cue"
 	"cuelang.org/go/cue/ast"
 	"cuelang.org/go/cue/ast/astutil"
 	"cuelang.org/go/internal"
 	"cuelang.org/go/internal/core/adt"
+	"cuelang.org/go/internal/core/debug"
 	"cuelang.org/go/internal/core/runtime"
 	"cuelang.org/go/internal/core/subsume"
 )
@@ -77,6 +81,8 @@ func Files(files []*ast.File, inst *cue.Instance, cfg *Config) error {
 		Config: *cfg,
 		ctx:    adt.NewContext(r, v),
 		remove: map[ast.Node]bool{},
+		debug:  Debug,
+		w:      os.Stderr,
 	}
 
 	t.findSubordinates(v)
@@ -102,11 +108,20 @@ type trimmer struct {
 
 	ctx    *adt.OpContext
 	remove map[ast.Node]bool
+
+	debug  bool
+	indent int
+	w      io.Writer
 }
 
+var Debug bool = false
+
 func (t *trimmer) markRemove(c adt.Conjunct) {
 	if src := c.Expr().Source(); src != nil {
 		t.remove[src] = true
+		if t.debug {
+			t.logf("removing %s", debug.NodeString(t.ctx, c.Expr(), nil))
+		}
 	}
 }
 
@@ -148,6 +163,8 @@ const (
 )
 
 func (t *trimmer) findSubordinates(v *adt.Vertex) int {
+	defer un(t.trace(v))
+
 	// TODO(structure sharing): do not descend into vertices whose parent is not
 	// equal to the parent. This is not relevant at this time, but may be so in
 	// the future.

tools/trim/trim_test.go

@@ -333,6 +333,8 @@ func TestX(t *testing.T) {
 
 	files := instances[0].Files
 
+	Debug = true
+
 	err := Files(files, inst, &Config{
 		Trace: true,
 	})