mirror of https://github.com/databricks/cli.git
118 lines
3.6 KiB
Go
118 lines
3.6 KiB
Go
package merge
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import (
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"fmt"
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"github.com/databricks/cli/libs/dyn"
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)
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// Merge recursively merges the specified values.
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//
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// Semantics are as follows:
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// * Merging x with nil or nil with x always yields x.
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// * Merging maps a and b means entries from map b take precedence.
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// * Merging sequences a and b means concatenating them.
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//
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// Merging retains and accumulates the locations metadata associated with the values.
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// This allows users of the module to track the provenance of values across merging of
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// configuration trees, which is useful for reporting errors and warnings.
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//
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// Semantics for location metadata in the merged value are similar to the semantics
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// for the values themselves:
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//
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// - When merging x with nil or nil with x, the location of x is retained.
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//
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// - When merging maps or sequences, the combined value retains the location of a and
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// accumulates the location of b. The individual elements of the map or sequence retain
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// their original locations, i.e., whether they were originally defined in a or b.
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//
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// The rationale for retaining location of a is that we would like to return
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// the first location a bit of configuration showed up when reporting errors and warnings.
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//
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// - Merging primitive values means using the incoming value `b`. The location of the
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// incoming value is retained and the location of the existing value `a` is accumulated.
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// This is because the incoming value overwrites the existing value.
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func Merge(a, b dyn.Value) (dyn.Value, error) {
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return merge(a, b)
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}
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func merge(a, b dyn.Value) (dyn.Value, error) {
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ak := a.Kind()
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bk := b.Kind()
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// If a is nil, return b.
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if ak == dyn.KindNil {
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return b.AppendLocationsFromValue(a), nil
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}
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// If b is nil, return a.
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if bk == dyn.KindNil {
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return a.AppendLocationsFromValue(b), nil
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}
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// Call the appropriate merge function based on the kind of a and b.
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switch ak {
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case dyn.KindMap:
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if bk != dyn.KindMap {
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return dyn.InvalidValue, fmt.Errorf("cannot merge map with %s", bk)
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}
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return mergeMap(a, b)
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case dyn.KindSequence:
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if bk != dyn.KindSequence {
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return dyn.InvalidValue, fmt.Errorf("cannot merge sequence with %s", bk)
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}
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return mergeSequence(a, b)
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default:
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if ak != bk {
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return dyn.InvalidValue, fmt.Errorf("cannot merge %s with %s", ak, bk)
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}
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return mergePrimitive(a, b)
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}
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}
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func mergeMap(a, b dyn.Value) (dyn.Value, error) {
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out := dyn.NewMapping()
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am := a.MustMap()
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bm := b.MustMap()
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// Add the values from a into the output map.
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out.Merge(am)
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// Merge the values from b into the output map.
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for _, pair := range bm.Pairs() {
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pk := pair.Key
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pv := pair.Value
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if ov, ok := out.Get(pk); ok {
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// If the key already exists, merge the values.
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merged, err := merge(ov, pv)
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if err != nil {
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return dyn.InvalidValue, err
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}
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out.Set(pk, merged)
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} else {
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// Otherwise, just set the value.
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out.Set(pk, pv)
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}
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}
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// Preserve the location of the first value. Accumulate the locations of the second value.
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return dyn.NewValue(out, a.Locations()).AppendLocationsFromValue(b), nil
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}
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func mergeSequence(a, b dyn.Value) (dyn.Value, error) {
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as := a.MustSequence()
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bs := b.MustSequence()
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// Merging sequences means concatenating them.
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out := make([]dyn.Value, len(as)+len(bs))
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copy(out[:], as)
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copy(out[len(as):], bs)
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// Preserve the location of the first value. Accumulate the locations of the second value.
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return dyn.NewValue(out, a.Locations()).AppendLocationsFromValue(b), nil
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}
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func mergePrimitive(a, b dyn.Value) (dyn.Value, error) {
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// Merging primitive values means using the incoming value.
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return b.AppendLocationsFromValue(a), nil
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}
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