Pass copy of dyn.Path to callback function (#1747)

## Changes

Some call sites hold on to the `dyn.Path` provided to them by the
callback. It must therefore never be mutated after the callback returns,
or these mutations leak out into unknown scope.

This change means it is no longer possible for this failure mode to
happen.

## Tests

Unit test.

bundle/artifacts/expand_globs.go

@@ -33,12 +33,7 @@ func createGlobError(v dyn.Value, p dyn.Path, message string) diag.Diagnostic {
 		Severity:  diag.Error,
 		Summary:   fmt.Sprintf("%s: %s", source, message),
 		Locations: []dyn.Location{v.Location()},
-
-		Paths: []dyn.Path{
-			// Hack to clone the path. This path copy is mutable.
-			// To be addressed in a later PR.
-			p.Append(),
-		},
+		Paths:     []dyn.Path{p},
 	}
 }
 

bundle/config/validate/unique_resource_keys.go

@@ -3,7 +3,6 @@ package validate
 import (
 	"context"
 	"fmt"
-	"slices"
 	"sort"
 
 	"github.com/databricks/cli/bundle"
@@ -66,10 +65,7 @@ func (m *uniqueResourceKeys) Apply(ctx context.Context, b *bundle.Bundle) diag.D
 				}
 			}
 
-			// dyn.Path under the hood is a slice. The code that walks the configuration
-			// tree uses the same underlying slice to track the path as it walks
-			// the tree. So, we need to clone it here.
-			m.paths = append(m.paths, slices.Clone(p))
+			m.paths = append(m.paths, p)
 			m.locations = append(m.locations, v.Locations()...)
 
 			resourceMetadata[k] = m

bundle/libraries/expand_glob_references.go

@@ -16,12 +16,10 @@ type expand struct {
 
 func matchError(p dyn.Path, l []dyn.Location, message string) diag.Diagnostic {
 	return diag.Diagnostic{
-		Severity: diag.Error,
-		Summary:  message,
-		Paths: []dyn.Path{
-			p.Append(),
-		},
+		Severity:  diag.Error,
+		Summary:   message,
 		Locations: l,
+		Paths:     []dyn.Path{p},
 	}
 }
 

bundle/libraries/upload.go

@@ -76,7 +76,7 @@ func collectLocalLibraries(b *bundle.Bundle) (map[string][]configLocation, error
 
 				source = filepath.Join(b.RootPath, source)
 				libs[source] = append(libs[source], configLocation{
-					configPath: p.Append(), // Hack to get the copy of path
+					configPath: p,
 					location:   v.Location(),
 				})
 

libs/dyn/visit.go

@@ -70,7 +70,7 @@ type visitOptions struct {
 
 func visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error) {
 	if len(suffix) == 0 {
-		return opts.fn(prefix, v)
+		return opts.fn(slices.Clone(prefix), v)
 	}
 
 	// Initialize prefix if it is empty.

libs/dyn/visit_map.go

@@ -21,7 +21,7 @@ func Foreach(fn MapFunc) MapFunc {
 			for _, pair := range m.Pairs() {
 				pk := pair.Key
 				pv := pair.Value
-				nv, err := fn(append(p, Key(pk.MustString())), pv)
+				nv, err := fn(p.Append(Key(pk.MustString())), pv)
 				if err != nil {
 					return InvalidValue, err
 				}
@@ -32,7 +32,7 @@ func Foreach(fn MapFunc) MapFunc {
 			s := slices.Clone(v.MustSequence())
 			for i, value := range s {
 				var err error
-				s[i], err = fn(append(p, Index(i)), value)
+				s[i], err = fn(p.Append(Index(i)), value)
 				if err != nil {
 					return InvalidValue, err
 				}

libs/dyn/visit_test.go

@@ -0,0 +1,36 @@
+package dyn_test
+
+import (
+	"testing"
+
+	"github.com/databricks/cli/libs/dyn"
+	assert "github.com/databricks/cli/libs/dyn/dynassert"
+)
+
+func TestVisitCallbackPathCopy(t *testing.T) {
+	vin := dyn.V(map[string]dyn.Value{
+		"foo": dyn.V(42),
+		"bar": dyn.V(43),
+	})
+
+	var paths []dyn.Path
+
+	// The callback should receive a copy of the path.
+	// If the same underlying value is used, all collected paths will be the same.
+	// This test uses `MapByPattern` to collect all paths in the map.
+	// Visit itself doesn't have public functions and we exclusively use black-box testing for this package.
+	_, _ = dyn.MapByPattern(vin, dyn.NewPattern(dyn.AnyKey()), func(p dyn.Path, v dyn.Value) (dyn.Value, error) {
+		paths = append(paths, p)
+		return v, nil
+	})
+
+	// Verify that the paths retained their original values.
+	var strings []string
+	for _, p := range paths {
+		strings = append(strings, p.String())
+	}
+	assert.ElementsMatch(t, strings, []string{
+		"foo",
+		"bar",
+	})
+}