Add `dyn.MapByPattern` to map a function to values with matching paths (#1266)

## Changes

The new `dyn.Pattern` type represents a path pattern that can match one
or more paths in a configuration tree. Every `dyn.Path` can be converted
to a `dyn.Pattern` that matches only a single path.

To accommodate this change, the visit function needed to be modified to
take a `dyn.Pattern` suffix. Every component in the pattern implements
an interface to work with the visit function. This function can recurse
on the visit function for one or more elements of the value being
visited. For patterns derived from a `dyn.Path`, it will work as it did
before and select the matching element. For the new pattern components
(e.g. `dyn.AnyKey` or `dyn.AnyIndex`), it recurses on all the elements
in the container.

## Tests

Unit tests. Confirmed full coverage for the new code.

libs/dyn/pattern.go

@@ -0,0 +1,96 @@
+package dyn
+
+import (
+	"fmt"
+	"maps"
+	"slices"
+)
+
+// Pattern represents a matcher for paths in a [Value] configuration tree.
+// It is used by [MapByPattern] to apply a function to the values whose paths match the pattern.
+// Every [Path] is a valid [Pattern] that matches a single unique path.
+// The reverse is not true; not every [Pattern] is a valid [Path], as patterns may contain wildcards.
+type Pattern []patternComponent
+
+// A pattern component can visit a [Value] and recursively call into [visit] for matching elements.
+// Fixed components can match a single key or index, while wildcards can match any key or index.
+type patternComponent interface {
+	visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error)
+}
+
+// NewPattern returns a new pattern from the given components.
+// The individual components may be created with [Key], [Index], or [Any].
+func NewPattern(cs ...patternComponent) Pattern {
+	return cs
+}
+
+// NewPatternFromPath returns a new pattern from the given path.
+func NewPatternFromPath(p Path) Pattern {
+	cs := make(Pattern, len(p))
+	for i, c := range p {
+		cs[i] = c
+	}
+	return cs
+}
+
+type anyKeyComponent struct{}
+
+// AnyKey returns a pattern component that matches any key.
+func AnyKey() patternComponent {
+	return anyKeyComponent{}
+}
+
+// This function implements the patternComponent interface.
+func (c anyKeyComponent) visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error) {
+	m, ok := v.AsMap()
+	if !ok {
+		return InvalidValue, fmt.Errorf("expected a map at %q, found %s", prefix, v.Kind())
+	}
+
+	m = maps.Clone(m)
+	for key, value := range m {
+		var err error
+		nv, err := visit(value, prefix.Append(Key(key)), suffix, opts)
+		if err != nil {
+			// Leave the value intact if the suffix pattern didn't match any value.
+			if IsNoSuchKeyError(err) || IsIndexOutOfBoundsError(err) {
+				continue
+			}
+			return InvalidValue, err
+		}
+		m[key] = nv
+	}
+
+	return NewValue(m, v.Location()), nil
+}
+
+type anyIndexComponent struct{}
+
+// AnyIndex returns a pattern component that matches any index.
+func AnyIndex() patternComponent {
+	return anyIndexComponent{}
+}
+
+// This function implements the patternComponent interface.
+func (c anyIndexComponent) visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error) {
+	s, ok := v.AsSequence()
+	if !ok {
+		return InvalidValue, fmt.Errorf("expected a sequence at %q, found %s", prefix, v.Kind())
+	}
+
+	s = slices.Clone(s)
+	for i, value := range s {
+		var err error
+		nv, err := visit(value, prefix.Append(Index(i)), suffix, opts)
+		if err != nil {
+			// Leave the value intact if the suffix pattern didn't match any value.
+			if IsNoSuchKeyError(err) || IsIndexOutOfBoundsError(err) {
+				continue
+			}
+			return InvalidValue, err
+		}
+		s[i] = nv
+	}
+
+	return NewValue(s, v.Location()), nil
+}

libs/dyn/pattern_test.go

@@ -0,0 +1,28 @@
+package dyn_test
+
+import (
+	"testing"
+
+	"github.com/databricks/cli/libs/dyn"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewPattern(t *testing.T) {
+	pat := dyn.NewPattern(
+		dyn.Key("foo"),
+		dyn.Index(1),
+	)
+
+	assert.Len(t, pat, 2)
+}
+
+func TestNewPatternFromPath(t *testing.T) {
+	path := dyn.NewPath(
+		dyn.Key("foo"),
+		dyn.Index(1),
+	)
+
+	pat1 := dyn.NewPattern(dyn.Key("foo"), dyn.Index(1))
+	pat2 := dyn.NewPatternFromPath(path)
+	assert.Equal(t, pat1, pat2)
+}

libs/dyn/visit.go

@@ -47,7 +47,7 @@ type visitOptions struct {
 	fn func(Path, Value) (Value, error)
 }
 
-func visit(v Value, prefix, suffix Path, opts visitOptions) (Value, error) {
+func visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error) {
 	if len(suffix) == 0 {
 		return opts.fn(prefix, v)
 	}
@@ -59,25 +59,31 @@ func visit(v Value, prefix, suffix Path, opts visitOptions) (Value, error) {
 	}
 
 	component := suffix[0]
-	prefix = prefix.Append(component)
 	suffix = suffix[1:]
 
+	// Visit the value with the current component.
+	return component.visit(v, prefix, suffix, opts)
+}
+
+func (component pathComponent) visit(v Value, prefix Path, suffix Pattern, opts visitOptions) (Value, error) {
+	path := prefix.Append(component)
+
 	switch {
 	case component.isKey():
 		// Expect a map to be set if this is a key.
 		m, ok := v.AsMap()
 		if !ok {
-			return InvalidValue, fmt.Errorf("expected a map to index %q, found %s", prefix, v.Kind())
+			return InvalidValue, fmt.Errorf("expected a map to index %q, found %s", path, v.Kind())
 		}
 
 		// Lookup current value in the map.
 		ev, ok := m[component.key]
 		if !ok {
-			return InvalidValue, noSuchKeyError{prefix}
+			return InvalidValue, noSuchKeyError{path}
 		}
 
 		// Recursively transform the value.
-		nv, err := visit(ev, prefix, suffix, opts)
+		nv, err := visit(ev, path, suffix, opts)
 		if err != nil {
 			return InvalidValue, err
 		}
@@ -100,17 +106,17 @@ func visit(v Value, prefix, suffix Path, opts visitOptions) (Value, error) {
 		// Expect a sequence to be set if this is an index.
 		s, ok := v.AsSequence()
 		if !ok {
-			return InvalidValue, fmt.Errorf("expected a sequence to index %q, found %s", prefix, v.Kind())
+			return InvalidValue, fmt.Errorf("expected a sequence to index %q, found %s", path, v.Kind())
 		}
 
 		// Lookup current value in the sequence.
 		if component.index < 0 || component.index >= len(s) {
-			return InvalidValue, indexOutOfBoundsError{prefix}
+			return InvalidValue, indexOutOfBoundsError{path}
 		}
 
 		// Recursively transform the value.
 		ev := s[component.index]
-		nv, err := visit(ev, prefix, suffix, opts)
+		nv, err := visit(ev, path, suffix, opts)
 		if err != nil {
 			return InvalidValue, err
 		}

libs/dyn/visit_get.go

@@ -14,7 +14,7 @@ func Get(v Value, path string) (Value, error) {
 // If the path doesn't exist, it returns InvalidValue and an error.
 func GetByPath(v Value, p Path) (Value, error) {
 	out := InvalidValue
-	_, err := visit(v, EmptyPath, p, visitOptions{
+	_, err := visit(v, EmptyPath, NewPatternFromPath(p), visitOptions{
 		fn: func(_ Path, ev Value) (Value, error) {
 			// Capture the value argument to return it.
 			out = ev

libs/dyn/visit_map.go

@@ -40,7 +40,7 @@ func Foreach(fn MapFunc) MapFunc {
 	}
 }
 
-// Map applies the given function to the value at the specified path in the specified value.
+// Map applies a function to the value at the given path in the given value.
 // It is identical to [MapByPath], except that it takes a string path instead of a [Path].
 func Map(v Value, path string, fn MapFunc) (Value, error) {
 	p, err := NewPathFromString(path)
@@ -50,15 +50,21 @@ func Map(v Value, path string, fn MapFunc) (Value, error) {
 	return MapByPath(v, p, fn)
 }
 
-// Map applies the given function to the value at the specified path in the specified value.
+// MapByPath applies a function to the value at the given path in the given value.
+// It is identical to [MapByPattern], except that it takes a [Path] instead of a [Pattern].
+// This means it only matches a single value, not a pattern of values.
+func MapByPath(v Value, p Path, fn MapFunc) (Value, error) {
+	return MapByPattern(v, NewPatternFromPath(p), fn)
+}
+
+// MapByPattern applies a function to the values whose paths match the given pattern in the given value.
 // If successful, it returns the new value with all intermediate values copied and updated.
 //
-// If the path contains a key that doesn't exist, or an index that is out of bounds,
-// it returns the original value and no error. This is because setting a value at a path
-// that doesn't exist is a no-op.
+// If the pattern contains a key that doesn't exist, or an index that is out of bounds,
+// it returns the original value and no error.
 //
-// If the path is invalid for the given value, it returns InvalidValue and an error.
-func MapByPath(v Value, p Path, fn MapFunc) (Value, error) {
+// If the pattern is invalid for the given value, it returns InvalidValue and an error.
+func MapByPattern(v Value, p Pattern, fn MapFunc) (Value, error) {
 	nv, err := visit(v, EmptyPath, p, visitOptions{
 		fn: fn,
 	})

libs/dyn/visit_map_test.go

@@ -268,3 +268,107 @@ func TestMapForeachOnOtherError(t *testing.T) {
 	}))
 	assert.ErrorContains(t, err, "expected a map or sequence, found int")
 }
+
+func TestMapByPatternOnNilValue(t *testing.T) {
+	var err error
+	_, err = dyn.MapByPattern(dyn.NilValue, dyn.NewPattern(dyn.AnyKey()), nil)
+	assert.ErrorContains(t, err, `expected a map at "", found nil`)
+	_, err = dyn.MapByPattern(dyn.NilValue, dyn.NewPattern(dyn.AnyIndex()), nil)
+	assert.ErrorContains(t, err, `expected a sequence at "", found nil`)
+}
+
+func TestMapByPatternOnMap(t *testing.T) {
+	vin := dyn.V(map[string]dyn.Value{
+		"a": dyn.V(map[string]dyn.Value{
+			"b": dyn.V(42),
+		}),
+		"b": dyn.V(map[string]dyn.Value{
+			"c": dyn.V(43),
+		}),
+	})
+
+	var err error
+
+	// Expect an error if the pattern structure doesn't match the value structure.
+	_, err = dyn.MapByPattern(vin, dyn.NewPattern(dyn.AnyKey(), dyn.Index(0)), nil)
+	assert.ErrorContains(t, err, `expected a sequence to index`)
+
+	// Apply function to pattern "*.b".
+	vout, err := dyn.MapByPattern(vin, dyn.NewPattern(dyn.AnyKey(), dyn.Key("b")), func(p dyn.Path, v dyn.Value) (dyn.Value, error) {
+		assert.Equal(t, dyn.NewPath(dyn.Key("a"), dyn.Key("b")), p)
+		assert.Equal(t, dyn.V(42), v)
+		return dyn.V(44), nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, map[string]any{
+		"a": map[string]any{
+			"b": 44,
+		},
+		"b": map[string]any{
+			"c": 43,
+		},
+	}, vout.AsAny())
+}
+
+func TestMapByPatternOnMapWithoutMatch(t *testing.T) {
+	vin := dyn.V(map[string]dyn.Value{
+		"a": dyn.V(map[string]dyn.Value{
+			"b": dyn.V(42),
+		}),
+		"b": dyn.V(map[string]dyn.Value{
+			"c": dyn.V(43),
+		}),
+	})
+
+	// Apply function to pattern "*.zzz".
+	vout, err := dyn.MapByPattern(vin, dyn.NewPattern(dyn.AnyKey(), dyn.Key("zzz")), nil)
+	assert.NoError(t, err)
+	assert.Equal(t, vin, vout)
+}
+
+func TestMapByPatternOnSequence(t *testing.T) {
+	vin := dyn.V([]dyn.Value{
+		dyn.V([]dyn.Value{
+			dyn.V(42),
+		}),
+		dyn.V([]dyn.Value{
+			dyn.V(43),
+			dyn.V(44),
+		}),
+	})
+
+	var err error
+
+	// Expect an error if the pattern structure doesn't match the value structure.
+	_, err = dyn.MapByPattern(vin, dyn.NewPattern(dyn.AnyIndex(), dyn.Key("a")), nil)
+	assert.ErrorContains(t, err, `expected a map to index`)
+
+	// Apply function to pattern "*.c".
+	vout, err := dyn.MapByPattern(vin, dyn.NewPattern(dyn.AnyIndex(), dyn.Index(1)), func(p dyn.Path, v dyn.Value) (dyn.Value, error) {
+		assert.Equal(t, dyn.NewPath(dyn.Index(1), dyn.Index(1)), p)
+		assert.Equal(t, dyn.V(44), v)
+		return dyn.V(45), nil
+	})
+	assert.NoError(t, err)
+	assert.Equal(t, []any{
+		[]any{42},
+		[]any{43, 45},
+	}, vout.AsAny())
+}
+
+func TestMapByPatternOnSequenceWithoutMatch(t *testing.T) {
+	vin := dyn.V([]dyn.Value{
+		dyn.V([]dyn.Value{
+			dyn.V(42),
+		}),
+		dyn.V([]dyn.Value{
+			dyn.V(43),
+			dyn.V(44),
+		}),
+	})
+
+	// Apply function to pattern "*.zzz".
+	vout, err := dyn.MapByPattern(vin, dyn.NewPattern(dyn.AnyIndex(), dyn.Index(42)), nil)
+	assert.NoError(t, err)
+	assert.Equal(t, vin, vout)
+}

libs/dyn/visit_set.go

@@ -25,10 +25,10 @@ func SetByPath(v Value, p Path, nv Value) (Value, error) {
 		return nv, nil
 	}
 
-	parent := p[:lp-1]
 	component := p[lp-1]
+	p = p[:lp-1]
 
-	return visit(v, EmptyPath, parent, visitOptions{
+	return visit(v, EmptyPath, NewPatternFromPath(p), visitOptions{
 		fn: func(prefix Path, v Value) (Value, error) {
 			path := prefix.Append(component)