internal/core/adt: patch performance issue related to error reporting

In V3, there are multiple points an error may be added
to the results. If an error ends up being added to more
than one path, it may duplicate, causing errors to
grow exponentially.

The real solution would be to only have single points
of entry. But for now we just dedup entries in the
low-level append function.

Fixes #3517

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I43f4531027f1e71d7e4610de3cd424b8a2dfda57
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1205368
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mpvl

cue/errors/errors.go

@@ -309,11 +309,19 @@ func appendToList(a list, err Error) list {
 	case nil:
 		return a
 	case list:
-		if a == nil {
+		if len(a) == 0 {
 			return x
 		}
-		return append(a, x...)
+		for _, e := range x {
+			a = appendToList(a, e)
+		}
+		return a
 	default:
+		for _, e := range a {
+			if e == err {
+				return a
+			}
+		}
 		return append(a, err)
 	}
 }

cue/testdata/benchmarks/issue3517.txtar

@@ -729,8 +729,9 @@ func runTask(t *task, mode runMode) {
 		} else {
 			t.state = taskFAILED
 		}
-		t.node.addBottom(t.err) // TODO: replace with something more principled.
-
+		// TODO: do not add both context and task errors. Do something more
+		// principled.
+		t.node.addBottom(t.err)
 		if t.id.cc != nil {
 			t.id.cc.decDependent(ctx, TASK, nil)
 		}

internal/core/adt/sched.go

@@ -915,7 +915,7 @@ diff old new
 -			name: "two"
 -		}
 -	}]
--	files: _|_ // invalid interpolation: cycle error (and 3 more errors)
+-	files: _|_ // invalid interpolation: cycle error (and 1 more errors)
 +	comprehension: _|_ // comprehension: key value of dynamic field must be concrete, found _|_(invalid interpolation: invalid interpolation: comprehension.filepath: undefined field: name) (and 1 more errors)
 +	complete: {
 +		x: "a foo z"
@@ -1173,7 +1173,7 @@ Improved error messages.
 			name: "two"
 		}
 	}]
-	files: _|_ // invalid interpolation: cycle error (and 3 more errors)
+	files: _|_ // invalid interpolation: cycle error (and 1 more errors)
 	scoped: {
 		direct: {
 			a: 1

internal/core/export/testdata/main/let.txtar

@@ -113,7 +113,7 @@ diff old new
  	s: strings.MinRunes(4) & strings.MaxRunes(7)
  	additional: {
  		env:   _
--		confs: _|_ // additional.confs: incomplete bool: _ (and 1 more errors)
+-		confs: _|_ // incomplete bool: _
 +		confs: _|_ // additional.confs: incomplete bool: _
  	}
  }
@@ -153,7 +153,7 @@ diff old new
 	s: strings.MinRunes(4) & strings.MaxRunes(7)
 	additional: {
 		env:   _
-		confs: _|_ // additional.confs: incomplete bool: _ (and 1 more errors)
+		confs: _|_ // incomplete bool: _
 	}
 }
 == All