tools/trim: only consider defaults when we're not ignoring the conjunct

If a conjunct has been marked to be ignored, then we should not consider
it even if it is a default for a disjunction.

This change does not prevent trimming of code due to defaults: there's a
specific defaults.txtar (which is unchanged) which shows the existence
of defaults can still lead to trimming.

Fixes: #3995

Change-Id: I0a693f2f14caf744f4d04ba39293b3871acdd71d
Signed-off-by: Matthew Sackman <[email protected]>
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1219302
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>

Author: cuematthew

tools/trim/testdata/64.txtar

@@ -0,0 +1,55 @@
+Disjunctions.
+
+If line 2 wasn't present,
+
+out: #Schema & {type: "A"}
+
+correctly gets simplified to
+
+out: #Schema & _
+
+because of the default.
+
+However, with line 2 present, simplifying `out` in the same way is incorrect.
+
+Note that v2 gets this wrong.
+
+-- a.cue --
+#Schema: {type: *"A" | string}
+#Schema: {type: "A"} | {type: "CNAME"}
+out: #Schema & {type: "A"}
+-- out/trim-v3 --
+== a.cue
+#Schema: {type: *"A" | string}
+#Schema: {type: "A"} | {type: "CNAME"}
+out: #Schema & {type: "A"}
+-- diff/-out/trim-v3<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,4 +1,4 @@
+ == a.cue
+ #Schema: {type: *"A" | string}
+ #Schema: {type: "A"} | {type: "CNAME"}
+-out: #Schema & {}
++out: #Schema & {type: "A"}
+-- out/trim-v3-noshare --
+== a.cue
+#Schema: {type: *"A" | string}
+#Schema: {type: "A"} | {type: "CNAME"}
+out: #Schema & {type: "A"}
+-- diff/-out/trim-v3-noshare<==>+out/trim --
+diff old new
+--- old
++++ new
+@@ -1,4 +1,4 @@
+ == a.cue
+ #Schema: {type: *"A" | string}
+ #Schema: {type: "A"} | {type: "CNAME"}
+-out: #Schema & {}
++out: #Schema & {type: "A"}
+-- out/trim --
+== a.cue
+#Schema: {type: *"A" | string}
+#Schema: {type: "A"} | {type: "CNAME"}
+out: #Schema & {}

tools/trim/trimv3.go

@@ -728,7 +728,7 @@ func (t *trimmerV3) findRedundancies(v *adt.Vertex, keepAll bool) {
 			}
 		}
 
-		if disj, ok := expr.(*adt.DisjunctionExpr); ok && disj.HasDefaults {
+		if disj, ok := expr.(*adt.DisjunctionExpr); !nm.ignoreConjunct && ok && disj.HasDefaults {
 			defaultCount := 0
 			matchingDefaultCount := 0
 			for _, branch := range disj.Values {