tools/trim: implement trim for evalv3

Trim now works on the result of evaluation for evalv3.

This new implementation only works for evalv3, and does not alter any
code paths for evalv2 and the existing trim.

The new implementation addresses all known bugs with trim.

Signed-off-by: Matthew Sackman <[email protected]>
Change-Id: If814b5f66ce2ea3ce37ddcbec71eb38f1bc97216
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1208658
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Marcel van Lohuizen <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

cmd/cue/cmd/testdata/script/trim_package.txtar

@@ -0,0 +1,63 @@
+exec cue mod init
+
+# -- evalv3 --
+env CUE_EXPERIMENT=evalv3=1
+exec cue trim -o - ./...
+cmp stdout expect-stdout-v3
+
+# -- evalv2 --
+env CUE_EXPERIMENT=evalv3=0
+exec cue trim -o - ./...
+cmp stdout expect-stdout-v2
+
+-- a.cue --
+package p
+
+x: y: int
+x: z: int
+-- b/b.cue --
+package p
+
+x: y: 7
+-- c/c.cue --
+package p
+
+x: z: 6
+-- expect-stdout-v3 --
+package p
+
+x: y: int
+x: z: int
+package p
+
+x: y: int
+x: z: int
+package p
+
+x: y: 7
+package p
+
+x: y: int
+x: z: int
+package p
+
+x: z: 6
+-- expect-stdout-v2 --
+package p
+
+x: y: int
+x: z: int
+package p
+
+x: y: int
+x: z: int
+package p
+
+x: y: 7
+package p
+
+x: y: int
+x: z: int
+package p
+
+x: z: 6

internal/core/subsume/vertex.go

@@ -291,6 +291,9 @@ func (s *subsumer) verticesDev(x, y *adt.Vertex) bool {
 			return true
 		}
 
+	case nil:
+		return false
+
 	default:
 		panic(fmt.Sprintf("unexpected type %T", v))
 	}

tools/trim/doc.go

@@ -0,0 +1,77 @@
+// Copyright 2025 The 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 removes some redundant values from CUE sources.
+//
+// The most common use of trim is to remove duplicate values from data
+// where a definition now provides the same value. For example:
+//
+//	servers: [
+//		{role: "web", cpus: 1},
+//		{role: "db", cpus: 1},
+//		{role: "proxy", cpus: 1},
+//	]
+//
+//	#server: {
+//		role: string
+//		cpus: 1
+//	}
+//
+//	servers: [...#server]
+//
+// Trim will simplify this to:
+//
+//	servers: [
+//		{role: "web"},
+//		{role: "db"},
+//		{role: "proxy"},
+//	]
+//
+//	#server: {
+//		role: string
+//		cpus: 1
+//	}
+//
+//	servers: [...#server]
+//
+// This works with defaults too. Given:
+//
+//	servers: [
+//		{role: "web", cpus: 1},
+//		{role: "db", cpus: 4},
+//		{role: "proxy", cpus: 1},
+//	]
+//
+//	#server: {
+//		role: string
+//		cpus: *1 | int
+//	}
+//
+//	servers: [...#server]
+//
+// Trim will simplify this to:
+//
+//	servers: [
+//		{role: "web"},
+//		{role: "db", cpus: 4},
+//		{role: "proxy"},
+//	]
+//
+//	#server: {
+//		role: string
+//		cpus: *1 | int
+//	}
+//
+//	servers: [...#server]
+package trim

tools/trim/testdata/1.txtar

@@ -0,0 +1,10 @@
+TODO. This should get simplified in the same way as 6, but
+doesn't. Possible bug in evaluator.
+
+-- a.cue --
+<10
+7
+-- out/trim --
+== a.cue
+<10
+7

tools/trim/testdata/10.txtar

@@ -0,0 +1,56 @@
+Similar to 9, but with list instead of struct. Note the simplification
+of the pattern too.
+
+See also 60.
+
+-- a.cue --
+d: [
+	{name: "jack",    age: 5},
+	{name: "gill",    age: >4},
+	{name: "hilbert", age: int},
+]
+d: [...{name: string, age: 5, age: number}]
+-- out/trim-v3 --
+== a.cue
+d: [
+	{name: "jack"},
+	{name: "gill"},
+	{name: "hilbert"},
+]
+d: [...{name: string, age: 5}]
+-- diff/-out/trim-v3<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -4,4 +4,4 @@
+ 	{name: "gill"},
+ 	{name: "hilbert"},
+ ]
+-d: [...{name: string, age: 5, age: number}]
++d: [...{name: string, age: 5}]
+-- out/trim-v3-noshare --
+== a.cue
+d: [
+	{name: "jack"},
+	{name: "gill"},
+	{name: "hilbert"},
+]
+d: [...{name: string, age: 5}]
+-- diff/-out/trim-v3-noshare<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -4,4 +4,4 @@
+ 	{name: "gill"},
+ 	{name: "hilbert"},
+ ]
+-d: [...{name: string, age: 5, age: number}]
++d: [...{name: string, age: 5}]
+-- out/trim --
+== a.cue
+d: [
+	{name: "jack"},
+	{name: "gill"},
+	{name: "hilbert"},
+]
+d: [...{name: string, age: 5, age: number}]

tools/trim/testdata/11.txtar

@@ -0,0 +1,30 @@
+Explicit unification of structs can lead to simplification.
+Contrast with 4.
+
+-- a.cue --
+x: {a: bool, b: "hi"} & {a: true, b: string}
+-- out/trim-v3 --
+== a.cue
+x: {b: "hi"} & {a: true}
+-- diff/-out/trim-v3<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: "hi"} & {a: true, b: string}
++x: {b: "hi"} & {a: true}
+-- out/trim-v3-noshare --
+== a.cue
+x: {b: "hi"} & {a: true}
+-- diff/-out/trim-v3-noshare<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: "hi"} & {a: true, b: string}
++x: {b: "hi"} & {a: true}
+-- out/trim --
+== a.cue
+x: {a: bool, b: "hi"} & {a: true, b: string}

tools/trim/testdata/12.txtar

@@ -0,0 +1,30 @@
+A variant of 11, with fields slightly rearranged. We do not currently
+simplify explicit unification where one side is top.
+
+-- a.cue --
+x: {a: bool, b: string} & {a: true, b: "hi"}
+-- out/trim-v3 --
+== a.cue
+x: _ & {a: true, b: "hi"}
+-- diff/-out/trim-v3<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: string} & {a: true, b: "hi"}
++x: _ & {a: true, b: "hi"}
+-- out/trim-v3-noshare --
+== a.cue
+x: _ & {a: true, b: "hi"}
+-- diff/-out/trim-v3-noshare<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: string} & {a: true, b: "hi"}
++x: _ & {a: true, b: "hi"}
+-- out/trim --
+== a.cue
+x: {a: bool, b: string} & {a: true, b: "hi"}

tools/trim/testdata/13.txtar

@@ -0,0 +1,30 @@
+A variant of 12, to ensure the ellipsis does not prevent
+simplification of the struct to top.
+
+-- a.cue --
+x: {a: bool, b: string, ...} & {a: true, b: "hi"}
+-- out/trim-v3 --
+== a.cue
+x: _ & {a: true, b: "hi"}
+-- diff/-out/trim-v3<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: string, ...} & {a: true, b: "hi"}
++x: _ & {a: true, b: "hi"}
+-- out/trim-v3-noshare --
+== a.cue
+x: _ & {a: true, b: "hi"}
+-- diff/-out/trim-v3-noshare<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: string, ...} & {a: true, b: "hi"}
++x: _ & {a: true, b: "hi"}
+-- out/trim --
+== a.cue
+x: {a: bool, b: string, ...} & {a: true, b: "hi"}

tools/trim/testdata/14.txtar

@@ -0,0 +1,30 @@
+Further variation on 11: make sure patterns are kept, even if they're
+not used.
+
+-- a.cue --
+x: {a: bool, b: string, [>"b"]: int} & {a: true, b: "hi"}
+-- out/trim-v3 --
+== a.cue
+x: {[>"b"]: int} & {a: true, b: "hi"}
+-- diff/-out/trim-v3<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: string, [>"b"]: int} & {a: true, b: "hi"}
++x: {[>"b"]: int} & {a: true, b: "hi"}
+-- out/trim-v3-noshare --
+== a.cue
+x: {[>"b"]: int} & {a: true, b: "hi"}
+-- diff/-out/trim-v3-noshare<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: {a: bool, b: string, [>"b"]: int} & {a: true, b: "hi"}
++x: {[>"b"]: int} & {a: true, b: "hi"}
+-- out/trim --
+== a.cue
+x: {a: bool, b: string, [>"b"]: int} & {a: true, b: "hi"}

tools/trim/testdata/15.txtar

@@ -0,0 +1,30 @@
+Similar to 11, but with lists: explicit unification of lists can lead
+to simplification.
+
+-- a.cue --
+x: [int, int, int] & [9, 8, 7]
+-- out/trim-v3 --
+== a.cue
+x: [_, _, _] & [9, 8, 7]
+-- diff/-out/trim-v3<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: [int, int, int] & [9, 8, 7]
++x: [_, _, _] & [9, 8, 7]
+-- out/trim-v3-noshare --
+== a.cue
+x: [_, _, _] & [9, 8, 7]
+-- diff/-out/trim-v3-noshare<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,2 +1,2 @@
+ == a.cue
+-x: [int, int, int] & [9, 8, 7]
++x: [_, _, _] & [9, 8, 7]
+-- out/trim --
+== a.cue
+x: [int, int, int] & [9, 8, 7]