all: remove support for list arithmetic

And adjust or remove tests that use list arithmetic.

This has a knock-on effect that in cuego, tags which indicate list
length are no longer supported. E.g. `cue:"3*[int|*1]"`. We cannot
automatically fix these use cases, but we also don't expect this change
to cause breakages as list arithmetic has been undocumented for years
and cuego tags tend to be simple expressions.

Some of the fixes to tests expose different bugs/limitations in evalv2,
though work fine with evalv3, so it's possible evalv2 users will
experience more bugs after this change. But these are only in very odd
semi-cyclic scenarios.

Note that this breaking language change is not based on
`language.version` from `cue.mod/module.cue`; the language spec has not
mentioned arithmetic on lists for years, and aligning the evaluator with
the spec has been planned for some time. Moreover, every CUE
configuration should be able to switch to `list.Concat` and
`list.Repeat`, for example via `cue fix`.

Fixes #2237

Signed-off-by: Matthew Sackman <[email protected]>
Change-Id: I39fe190ac2131f60734f91485474e9c94758367f
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1200221
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: cuematthew

Diff for: cue/testdata/basicrewrite/011_list_arithmetic.txtar

@@ -1,12 +1,14 @@
 -- in.cue --
 package main
 
+import "list"
+
 #d1: {
 	as: [...string]
 
 	#c: [
 		#f1 & {
-			"as": ["go"] + as
+			"as": list.Concat([["go"], as])
 		},
 	]
 }
@@ -41,15 +43,15 @@ package main
 	from: #c1
 }
 -- out/eval/stats --
-Leaks:  9
-Freed:  55
-Reused: 41
-Allocs: 23
-Retain: 14
+Leaks:  0
+Freed:  85
+Reused: 70
+Allocs: 15
+Retain: 7
 
-Unifications: 52
-Conjuncts:    120
-Disjuncts:    66
+Unifications: 65
+Conjuncts:    159
+Disjuncts:    92
 -- out/evalalpha --
 (struct){
   #d1: (#struct){
@@ -239,9 +241,12 @@ Reordering
     ]
     #c: [
       (〈2;#f1〉 & {
-        as: ([
-          "go",
-        ] + 〈2;as〉)
+        as: 〈import;list〉.Concat([
+          [
+            "go",
+          ],
+          〈3;as〉,
+        ])
       }),
     ]
   }

Diff for: cue/testdata/comprehensions/issue843.txtar

@@ -30,7 +30,7 @@ chain: t2: p1: {
 	X: 1
 
 	// Reference X through x.x0 before X is inserted.
-	for v in [0, X] + [] {
+	for v in list.Concat([[0, X], []]) {
 		x: "x\(v)": {}
 	}
 
@@ -41,7 +41,7 @@ chain: t2: p1: {
 
 chain: t2: p2: {
 	// Reference X through x.x0 before X is inserted.
-	for v in [0, X] + [] {
+	for v in list.Concat([[0, X], []]) {
 		x: "x\(v)": {}
 	}
 
@@ -208,14 +208,14 @@ issue2052: full: {
 	d: #Depth & {#in: tree}
 }
 -- out/evalalpha/stats --
-Leaks:  19997
+Leaks:  19999
 Freed:  1462
 Reused: 1461
-Allocs: 19998
+Allocs: 20000
 Retain: 0
 
-Unifications: 7504
-Conjuncts:    107530
+Unifications: 7506
+Conjuncts:    107540
 Disjuncts:    13655
 -- out/evalalpha --
 Errors:
@@ -720,22 +720,22 @@ diff old new
 --- old
 +++ new
 @@ -1,9 +1,9 @@
--Leaks:  70
--Freed:  1815
--Reused: 1801
--Allocs: 84
--Retain: 185
-+Leaks:  19997
+-Leaks:  56
+-Freed:  1830
+-Reused: 1816
+-Allocs: 70
+-Retain: 169
++Leaks:  19999
 +Freed:  1462
 +Reused: 1461
-+Allocs: 19998
++Allocs: 20000
 +Retain: 0
 
--Unifications: 800
--Conjuncts:    3175
--Disjuncts:    1974
-+Unifications: 7504
-+Conjuncts:    107530
+-Unifications: 801
+-Conjuncts:    3177
+-Disjuncts:    1979
++Unifications: 7506
++Conjuncts:    107540
 +Disjuncts:    13655
 -- diff/-out/evalalpha<==>+out/eval --
 diff old new
@@ -755,7 +755,28 @@ diff old new
    chain: (struct){
      t1: (struct){
        #maxiter: (int){ 2 }
-@@ -47,148 +55,148 @@
+@@ -27,15 +35,11 @@
+           }
+         }
+       }
+-      p2: (_|_){
+-        // [incomplete] 1: invalid interpolation: cycle error referencing X:
+-        //     ./in.cue:44:6
+-        //     ./in.cue:43:28
+-        x: (_|_){
+-          // [incomplete] 1: invalid interpolation: cycle error referencing X:
+-          //     ./in.cue:44:6
+-          //     ./in.cue:43:28
+-          x0: (struct){
++      p2: (struct){
++        x: (struct){
++          x0: (struct){
++          }
++          x1: (struct){
+           }
+         }
+         X: (int){ 1 }
+@@ -51,148 +55,148 @@
        }
      }
    }
@@ -1041,7 +1062,7 @@ diff old new
          #maxiter: (int){ |(*(int){ 4 }, (int){ &(>=0, int) }) }
          #funcFactory: (#struct){
            #next: (_){ _ }
-@@ -335,49 +343,7 @@
+@@ -339,49 +343,7 @@
          }
          cow: (string){ "moo" }
        }
@@ -1092,7 +1113,7 @@ diff old new
          #in: (#struct){
            a: (#struct){
              foo: (string){ "bar" }
-@@ -389,6 +355,142 @@
+@@ -393,6 +355,142 @@
            }
            cow: (string){ "moo" }
          }
@@ -1236,15 +1257,15 @@ diff old new
      }
    }
 -- out/eval/stats --
-Leaks:  70
-Freed:  1815
-Reused: 1801
-Allocs: 84
-Retain: 185
+Leaks:  56
+Freed:  1830
+Reused: 1816
+Allocs: 70
+Retain: 169
 
-Unifications: 800
-Conjuncts:    3175
-Disjuncts:    1974
+Unifications: 801
+Conjuncts:    3177
+Disjuncts:    1979
 -- diff/todo/p1 --
 issue2052.*.#Depth: incorrect error message:
 	"adding field #basic not allowed as field set was already referenced"
@@ -1280,12 +1301,16 @@ issue2052.full.d: "cannot add field #maxiter: was already used"
           }
         }
       }
-      p2: (struct){
-        x: (struct){
+      p2: (_|_){
+        // [incomplete] 1: invalid interpolation: cycle error referencing X:
+        //     ./in.cue:44:6
+        //     ./in.cue:43:28
+        x: (_|_){
+          // [incomplete] 1: invalid interpolation: cycle error referencing X:
+          //     ./in.cue:44:6
+          //     ./in.cue:43:28
           x0: (struct){
           }
-          x1: (struct){
-          }
         }
         X: (int){ 1 }
       }
@@ -1676,10 +1701,13 @@ issue2052.full.d: "cannot add field #maxiter: was already used"
     t2: {
       p1: {
         X: 1
-        for _, v in ([
-          0,
-          〈1;X〉,
-        ] + []) {
+        for _, v in 〈import;list〉.Concat([
+          [
+            0,
+            〈2;X〉,
+          ],
+          [],
+        ]) {
           x: {
             "x\(〈2;v〉)": {}
           }
@@ -1692,10 +1720,13 @@ issue2052.full.d: "cannot add field #maxiter: was already used"
   chain: {
     t2: {
       p2: {
-        for _, v in ([
-          0,
-          〈1;X〉,
-        ] + []) {
+        for _, v in 〈import;list〉.Concat([
+          [
+            0,
+            〈2;X〉,
+          ],
+          [],
+        ]) {
           x: {
             "x\(〈2;v〉)": {}
           }