pkg/list: add Reverse function

This CL adds a list.Reverse function which reverses a list. It mirrors
the Golang slices.Reverse function.

Also, a typo in the func doc for SortStrings is fixed.

Closes #2505.

Signed-off-by: Noam Dolovich <[email protected]>
Change-Id: I6ef95952a51413c4188919ebbda94804e9635e73
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1196212
Reviewed-by: Daniel Martí <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

pkg/list/list.go

@@ -17,6 +17,7 @@ package list
 
 import (
 	"fmt"
+	"slices"
 	"sort"
 
 	"cuelang.org/go/cue"
@@ -215,6 +216,20 @@ func Slice(x []cue.Value, i, j int) ([]cue.Value, error) {
 	return x[i:j], nil
 }
 
+// Reverse reverses a list.
+//
+// For instance:
+//
+//	Reverse([1, 2, 3, 4])
+//
+// results in
+//
+//	[4, 3, 2, 1]
+func Reverse(x []cue.Value) []cue.Value {
+	slices.Reverse(x)
+	return x
+}
+
 // MinItems reports whether a has at least n items.
 func MinItems(list pkg.List, n int) (bool, error) {
 	count := len(list.Elems())

pkg/list/sort.go

@@ -218,7 +218,7 @@ func SortStable(list []cue.Value, cmp cue.Value) (sorted []cue.Value, err error)
 	return s.ret()
 }
 
-// Strings sorts a list of strings in increasing order.
+// SortStrings sorts a list of strings in increasing order.
 func SortStrings(a []string) []string {
 	sort.Strings(a)
 	return a

pkg/list/testdata/list.txtar

@@ -59,6 +59,17 @@ maxItems: {
 	fail1: [0, 1]
 }
 
+reverse: {
+    [string]: {x: _, v: list.Reverse(x)}
+
+    t1: x: []
+    t2: x: [1]
+    t3: x: [1, 2, 3, 4]
+
+    fail1: x: 1
+    fail2: x: "bad"
+}
+
 -- out/list-v3 --
 Errors:
 repeat.t8.v: error in call to list.Repeat: negative count:
@@ -74,6 +85,10 @@ minItems.fail1: invalid value [] (does not satisfy list.MinItems(1)): len(list)
 maxItems.fail1: invalid value [0,1] (does not satisfy list.MaxItems(1)): len(list) > MaxItems(1) (2 > 1):
     ./in.cue:53:12
     ./in.cue:53:26
+reverse.fail1.v: cannot use 1 (type int) as list in argument 1 to list.Reverse:
+    ./in.cue:68:15
+reverse.fail2.v: cannot use "bad" (type string) as list in argument 1 to list.Reverse:
+    ./in.cue:69:15
 
 Result:
 import "list"
@@ -176,6 +191,28 @@ maxItems: {
 	ok3: [0, ...]
 	fail1: _|_ // maxItems.fail1: invalid value [0,1] (does not satisfy list.MaxItems(1)): len(list) > MaxItems(1) (2 > 1)
 }
+reverse: {
+	t1: {
+		x: []
+		v: []
+	}
+	t2: {
+		x: [1]
+		v: [1]
+	}
+	t3: {
+		x: [1, 2, 3, 4]
+		v: [4, 3, 2, 1]
+	}
+	fail1: {
+		x: 1
+		v: _|_ // reverse.fail1.v: cannot use 1 (type int) as list in argument 1 to list.Reverse
+	}
+	fail2: {
+		x: "bad"
+		v: _|_ // reverse.fail2.v: cannot use "bad" (type string) as list in argument 1 to list.Reverse
+	}
+}
 -- diff/-out/list-v3<==>+out/list --
 diff old new
 --- old
@@ -189,9 +226,9 @@ diff old new
      ./in.cue:53:12
      ./in.cue:53:26
 -    ./in.cue:58:9
-
- Result:
- import "list"
+ reverse.fail1.v: cannot use 1 (type int) as list in argument 1 to list.Reverse:
+     ./in.cue:68:15
+ reverse.fail2.v: cannot use "bad" (type string) as list in argument 1 to list.Reverse:
 -- diff/todo/p2 --
 Missing error positions.
 -- out/list --
@@ -211,6 +248,10 @@ maxItems.fail1: invalid value [0,1] (does not satisfy list.MaxItems(1)): len(lis
     ./in.cue:53:12
     ./in.cue:53:26
     ./in.cue:58:9
+reverse.fail1.v: cannot use 1 (type int) as list in argument 1 to list.Reverse:
+    ./in.cue:68:15
+reverse.fail2.v: cannot use "bad" (type string) as list in argument 1 to list.Reverse:
+    ./in.cue:69:15
 
 Result:
 import "list"
@@ -313,3 +354,25 @@ maxItems: {
 	ok3: [0, ...]
 	fail1: _|_ // maxItems.fail1: invalid value [0,1] (does not satisfy list.MaxItems(1)): len(list) > MaxItems(1) (2 > 1)
 }
+reverse: {
+	t1: {
+		x: []
+		v: []
+	}
+	t2: {
+		x: [1]
+		v: [1]
+	}
+	t3: {
+		x: [1, 2, 3, 4]
+		v: [4, 3, 2, 1]
+	}
+	fail1: {
+		x: 1
+		v: _|_ // reverse.fail1.v: cannot use 1 (type int) as list in argument 1 to list.Reverse
+	}
+	fail2: {
+		x: "bad"
+		v: _|_ // reverse.fail2.v: cannot use "bad" (type string) as list in argument 1 to list.Reverse
+	}
+}