diff --git a/cue/testdata/cycle/comprehension.txtar b/cue/testdata/cycle/comprehension.txtar
index 924e30668..c4cbb172a 100644
--- a/cue/testdata/cycle/comprehension.txtar
+++ b/cue/testdata/cycle/comprehension.txtar
@@ -310,23 +310,19 @@ issue2367: {
 }
 
 -- out/evalalpha/stats --
-Leaks:  778
+Leaks:  782
 Freed:  63
 Reused: 63
-Allocs: 778
+Allocs: 782
 Retain: 0
 
-Unifications: 498
-Conjuncts:    2977
+Unifications: 502
+Conjuncts:    3031
 Disjuncts:    196
 -- out/evalalpha --
 Errors:
 selfReferential.insertionError.A: adding field foo3 not allowed as field set was already referenced:
     ./in.cue:117:14
-siblingInsertion.t2.p1.deployment: adding field logging not allowed as field set was already referenced:
-    ./in.cue:277:21
-siblingInsertion.t2.p2.deployment: adding field logging not allowed as field set was already referenced:
-    ./in.cue:292:21
 
 Result:
 (_|_){
@@ -651,8 +647,7 @@ Result:
       }
     }
   }
-  siblingInsertion: (_|_){
-    // [eval]
+  siblingInsertion: (struct){
     t1: (struct){
       p1: (struct){
         D: (struct){
@@ -685,28 +680,35 @@ Result:
         }
       }
     }
-    t2: (_|_){
-      // [eval]
-      p1: (_|_){
-        // [eval] siblingInsertion.t2.p1.deployment: adding field logging not allowed as field set was already referenced:
-        //     ./in.cue:277:21
+    t2: (struct){
+      p1: (struct){
         D: (struct){
           logging: (_){ _ }
         }
-        deployment: (_|_){
-          // [eval] siblingInsertion.t2.p1.deployment: adding field logging not allowed as field set was already referenced:
-          //     ./in.cue:277:21
+        deployment: (struct){
+          logging: (struct){
+            env2: (struct){
+              ENV: (string){ "True" }
+            }
+            env: (struct){
+              ENV: (string){ "True" }
+            }
+          }
         }
       }
-      p2: (_|_){
-        // [eval] siblingInsertion.t2.p2.deployment: adding field logging not allowed as field set was already referenced:
-        //     ./in.cue:292:21
+      p2: (struct){
         D: (struct){
           logging: (_){ _ }
         }
-        deployment: (_|_){
-          // [eval] siblingInsertion.t2.p2.deployment: adding field logging not allowed as field set was already referenced:
-          //     ./in.cue:292:21
+        deployment: (struct){
+          logging: (struct){
+            env2: (struct){
+              ENV: (string){ "True" }
+            }
+            env: (struct){
+              ENV: (string){ "True" }
+            }
+          }
         }
       }
     }
@@ -719,19 +721,15 @@ Result:
 diff old new
 --- old
 +++ new
-@@ -1,5 +1,10 @@
+@@ -1,5 +1,6 @@
  Errors:
 -selfReferential.insertionError.A: field foo3 not allowed by earlier comprehension or reference cycle
 +selfReferential.insertionError.A: adding field foo3 not allowed as field set was already referenced:
 +    ./in.cue:117:14
-+siblingInsertion.t2.p1.deployment: adding field logging not allowed as field set was already referenced:
-+    ./in.cue:277:21
-+siblingInsertion.t2.p2.deployment: adding field logging not allowed as field set was already referenced:
-+    ./in.cue:292:21
  
  Result:
  (_|_){
-@@ -19,7 +24,9 @@
+@@ -19,7 +20,9 @@
    B: (struct){
      a: (struct){
        parent: (string){ "" }
@@ -742,7 +740,7 @@ diff old new
        }
      }
    }
-@@ -52,17 +59,12 @@
+@@ -52,17 +55,12 @@
        }
      }
      _e: (#struct){
@@ -766,7 +764,7 @@ diff old new
        }
      }
      e: (#struct){
-@@ -76,12 +78,7 @@
+@@ -76,12 +74,7 @@
        }
        f2: (#struct){
          a: (#struct){
@@ -780,7 +778,7 @@ diff old new
          }
        }
      }
-@@ -127,9 +124,9 @@
+@@ -127,9 +120,9 @@
      insertionError: (_|_){
        // [eval]
        A: (_|_){
@@ -792,7 +790,7 @@ diff old new
        }
      }
      acrossOr: (struct){
-@@ -254,27 +251,31 @@
+@@ -254,27 +247,31 @@
    issue1881: (struct){
      p1: (struct){
        o: (#struct){
@@ -845,7 +843,7 @@ diff old new
          }) }
      }
      p2: (struct){
-@@ -290,7 +291,7 @@
+@@ -290,7 +287,7 @@
          }
        }
        o: (#struct){
@@ -854,90 +852,15 @@ diff old new
            output: (#struct){
              reject: (string){ "ok" }
            }
-@@ -320,15 +321,16 @@
+@@ -320,7 +317,7 @@
            resource: (string){ string }
          }) }
        o: (#struct){
 -        retry: (#struct){
--          output: (#struct){
--            reject: (string){ "ok" }
--          }
--        }
--      }
--    }
--  }
--  siblingInsertion: (struct){
 +        retry: (struct){
-+          output: (#struct){
-+            reject: (string){ "ok" }
-+          }
-+        }
-+      }
-+    }
-+  }
-+  siblingInsertion: (_|_){
-+    // [eval]
-     t1: (struct){
-       p1: (struct){
-         D: (struct){
-@@ -361,35 +363,28 @@
-         }
-       }
-     }
--    t2: (struct){
--      p1: (struct){
--        D: (struct){
--          logging: (_){ _ }
--        }
--        deployment: (struct){
--          logging: (struct){
--            env2: (struct){
--              ENV: (string){ "True" }
--            }
--            env: (struct){
--              ENV: (string){ "True" }
--            }
--          }
--        }
--      }
--      p2: (struct){
--        D: (struct){
--          logging: (_){ _ }
--        }
--        deployment: (struct){
--          logging: (struct){
--            env2: (struct){
--              ENV: (string){ "True" }
--            }
--            env: (struct){
--              ENV: (string){ "True" }
--            }
--          }
-+    t2: (_|_){
-+      // [eval]
-+      p1: (_|_){
-+        // [eval] siblingInsertion.t2.p1.deployment: adding field logging not allowed as field set was already referenced:
-+        //     ./in.cue:277:21
-+        D: (struct){
-+          logging: (_){ _ }
-+        }
-+        deployment: (_|_){
-+          // [eval] siblingInsertion.t2.p1.deployment: adding field logging not allowed as field set was already referenced:
-+          //     ./in.cue:277:21
-+        }
-+      }
-+      p2: (_|_){
-+        // [eval] siblingInsertion.t2.p2.deployment: adding field logging not allowed as field set was already referenced:
-+        //     ./in.cue:292:21
-+        D: (struct){
-+          logging: (_){ _ }
-+        }
-+        deployment: (_|_){
-+          // [eval] siblingInsertion.t2.p2.deployment: adding field logging not allowed as field set was already referenced:
-+          //     ./in.cue:292:21
-         }
-       }
-     }
+           output: (#struct){
+             reject: (string){ "ok" }
+           }
 -- diff/-out/evalalpha/stats<==>+out/eval/stats --
 diff old new
 --- old
@@ -948,17 +871,17 @@ diff old new
 -Reused: 1260
 -Allocs: 60
 -Retain: 145
-+Leaks:  778
++Leaks:  782
 +Freed:  63
 +Reused: 63
-+Allocs: 778
++Allocs: 782
 +Retain: 0
  
 -Unifications: 832
 -Conjuncts:    2525
 -Disjuncts:    1404
-+Unifications: 498
-+Conjuncts:    2977
++Unifications: 502
++Conjuncts:    3031
 +Disjuncts:    196
 -- out/eval/stats --
 Leaks:  50
@@ -972,8 +895,6 @@ Conjuncts:    2525
 Disjuncts:    1404
 -- diff/explanation --
 B.a.children: now correctly marked as incomplete
--- diff/todo/p0 --
-siblingInsertion.t2: errors
 -- diff/todo/p2 --
 issue1881.#AllOutputs.retry: additional entry.
 Might be error in practice and okay.
diff --git a/cue/testdata/cycle/freeze.txtar b/cue/testdata/cycle/freeze.txtar
index 3997ee7e7..3f34ede6f 100644
--- a/cue/testdata/cycle/freeze.txtar
+++ b/cue/testdata/cycle/freeze.txtar
@@ -158,8 +158,6 @@ comprehension.t3.err.a: adding field xq not allowed as field set was already ref
     ./comprehension.cue:82:13
 comprehension.moreSpecific.err.a.x: adding field z not allowed as field set was already referenced:
     ./comprehension.cue:114:9
-issue3178.output: adding field Value not allowed as field set was already referenced:
-    ./issue3178.cue:9:23
 
 Result:
 (_|_){
@@ -295,15 +293,12 @@ Result:
       }
     }
   }
-  issue3178: (_|_){
-    // [eval] issue3178.output: adding field Value not allowed as field set was already referenced:
-    //     ./issue3178.cue:9:23
+  issue3178: (struct){
     input: (#list){
       0: (string){ "Value" }
     }
-    output: (_|_){
-      // [eval] issue3178.output: adding field Value not allowed as field set was already referenced:
-      //     ./issue3178.cue:9:23
+    output: (struct){
+      Value: (bool){ true }
     }
   }
 }
@@ -311,7 +306,7 @@ Result:
 diff old new
 --- old
 +++ new
-@@ -1,11 +1,12 @@
+@@ -1,11 +1,10 @@
  Errors:
 -comprehension.moreSpecific.err.a: field z not allowed by earlier comprehension or reference cycle
 -comprehension.t1.ok.p0.x: field z not allowed by earlier comprehension or reference cycle
@@ -326,12 +321,10 @@ diff old new
 +    ./comprehension.cue:82:13
 +comprehension.moreSpecific.err.a.x: adding field z not allowed as field set was already referenced:
 +    ./comprehension.cue:114:9
-+issue3178.output: adding field Value not allowed as field set was already referenced:
-+    ./issue3178.cue:9:23
  
  Result:
  (_|_){
-@@ -12,73 +13,65 @@
+@@ -12,73 +11,65 @@
    // [eval]
    comprehension: (_|_){
      // [eval]
@@ -455,7 +448,7 @@ diff old new
              }
            }
          }
-@@ -89,9 +82,9 @@
+@@ -89,9 +80,9 @@
        err: (_|_){
          // [eval]
          a: (_|_){
@@ -468,7 +461,7 @@ diff old new
          }
        }
      }
-@@ -99,16 +92,14 @@
+@@ -99,16 +90,14 @@
        // [eval]
        err: (_|_){
          // [eval]
@@ -491,7 +484,7 @@ diff old new
          }
        }
      }
-@@ -132,10 +123,10 @@
+@@ -132,10 +121,10 @@
        err: (_|_){
          // [eval]
          a: (_|_){
@@ -504,27 +497,6 @@ diff old new
            }
          }
        }
-@@ -151,12 +142,15 @@
-       }
-     }
-   }
--  issue3178: (struct){
-+  issue3178: (_|_){
-+    // [eval] issue3178.output: adding field Value not allowed as field set was already referenced:
-+    //     ./issue3178.cue:9:23
-     input: (#list){
-       0: (string){ "Value" }
-     }
--    output: (struct){
--      Value: (bool){ true }
-+    output: (_|_){
-+      // [eval] issue3178.output: adding field Value not allowed as field set was already referenced:
-+      //     ./issue3178.cue:9:23
-     }
-   }
- }
--- diff/todo/p3 --
-Error path location could improve.
 -- diff/explanation --
 v0.7 fixes bugs in v0.6:
 - t1 should be incomplete error, as it is fixable.
diff --git a/internal/core/adt/expr.go b/internal/core/adt/expr.go
index 09d8ea90e..97a58a1ca 100644
--- a/internal/core/adt/expr.go
+++ b/internal/core/adt/expr.go
@@ -2026,7 +2026,13 @@ func (c *OpContext) forSource(x Expr) *Vertex {
 
 	node, ok := v.(*Vertex)
 	if ok && c.isDevVersion() {
-		node.unify(c, state.conditions(), yield)
+		// We do not request to "yield" here, but rather rely on the
+		// call-by-need behavior in combination with the freezing mechanism.
+		// TODO: this seems a bit fragile. At some point we need to make this
+		// more robust by moving to a pure call-by-need mechanism, for instance.
+		// TODO: using attemptOnly here will remove the cyclic reference error
+		// of comprehension.t1.ok (which also errors in V2),
+		node.unify(c, state.conditions(), finalize)
 	}
 
 	v, ok = c.getDefault(v)
@@ -2064,7 +2070,7 @@ func (c *OpContext) forSource(x Expr) *Vertex {
 		}
 
 	default:
-		if kind := v.Kind(); kind&StructKind != 0 {
+		if kind := v.Kind(); kind&(StructKind|ListKind) != 0 {
 			c.addErrf(IncompleteError, pos(x),
 				"cannot range over %s (incomplete type %s)", x, kind)
 			return emptyNode
@@ -2076,6 +2082,17 @@ func (c *OpContext) forSource(x Expr) *Vertex {
 			return emptyNode
 		}
 	}
+	if c.isDevVersion() {
+		kind := v.Kind()
+		// At this point it is possible that the Vertex represents an incomplete
+		// struct or list, which is the case if it may be struct or list, but
+		// is also at least some other type, such as is the case with top.
+		if kind&(StructKind|ListKind) != 0 && kind != StructKind && kind != ListKind {
+			c.addErrf(IncompleteError, pos(x),
+				"cannot range over %s (incomplete type %s)", x, kind)
+			return emptyNode
+		}
+	}
 
 	return node
 }
diff --git a/internal/core/export/testdata/main/adt.txtar b/internal/core/export/testdata/main/adt.txtar
index 941e4c6d7..3832c035f 100644
--- a/internal/core/export/testdata/main/adt.txtar
+++ b/internal/core/export/testdata/main/adt.txtar
@@ -253,6 +253,107 @@ errorListDef: {
 }
 -- diff/doc/explanation --
 Reordering.
+-- out/doc-v3 --
+[]
+[p1]
+[d1]
+[d1 foobar]
+[bar]
+[d2]
+[d2 foobar]
+[d2 foobar name]
+[d2 foobar foo]
+[a]
+- Issue #1910
+
+[comp]
+[comp bar]
+[bytes]
+[c1]
+[s1]
+[l1]
+[l1 0]
+[l2]
+[l3]
+[l4]
+[l4 0]
+[l4 1]
+[l5]
+[l5 #foo]
+[l5 0]
+[l5 1]
+[#foo]
+[l6]
+[l6 #foo]
+[l6 0]
+[l6 1]
+[n1]
+[n10]
+[t]
+- t is true
+
+[e1]
+[e2]
+[e3]
+[e4]
+[e5]
+[e6]
+[e7]
+[e8]
+[m1]
+[m1 foo]
+- foo is an optional field
+
+[m1 bar]
+- bar is a field
+
+[m1 baz]
+- baz is a required field.
+
+[x]
+[y1]
+[y1 src]
+[y1 src 0]
+[y1 src 1]
+[y1 src 2]
+[y1 x]
+[y1 x 0]
+[y1 x 1]
+[y1 x 2]
+[y1 foo0]
+[y1 foo1]
+[y1 foo2]
+[y1 bar1]
+[y1 bar2]
+[preserveKeyFieldInComprehension]
+[errorStructDef]
+[errorStructDef a]
+[errorStructDef b]
+[errorStructDef #Def]
+[errorList]
+[errorList 0]
+[errorList 1]
+[errorListDef]
+[errorListDef #Def]
+[errorListDef 0]
+[errorListDef 1]
+-- diff/-out/doc-v3<==>+out/doc --
+diff old new
+--- old
++++ new
+@@ -65,10 +65,10 @@
+ [y1 x 1]
+ [y1 x 2]
+ [y1 foo0]
+-[y1 bar1]
+-[y1 bar2]
+ [y1 foo1]
+ [y1 foo2]
++[y1 bar1]
++[y1 bar2]
+ [preserveKeyFieldInComprehension]
+ [errorStructDef]
+ [errorStructDef a]
 -- out/doc --
 []
 [p1]
@@ -339,6 +440,123 @@ Reordering.
 [errorListDef 1]
 -- diff/value/todo/p3 --
 Error message change.
+-- out/value-v3 --
+== Simplified
+_|_ // e3: index out of range [2] with length 2
+== Raw
+_|_ // e3: index out of range [2] with length 2
+== Final
+_|_ // e3: index out of range [2] with length 2
+== All
+{
+	@foo(bar)
+	p1: {}
+	d1: {
+		foobar: int
+	}
+	bar: "bar"
+	d2: {
+		foobar: {
+			name: "xx"
+			foo:  "xx"
+		}
+	}
+
+	// Issue #1910
+	a: _
+	comp: {
+		for k, v in [0]
+		let w = v {
+			"\(a)": w
+			"bar":  w
+		}
+	}
+	bytes: '\xeb \x1a\xf5\xaa\xf0\xd6\x06)'
+	c1:    true
+	s1: """
+		multi
+		bar
+		line
+		"""
+	l1: [3, ...int]
+	l2: [...int]
+	l3: []
+	l4: [1, 2]
+	l5: {
+		#foo: int
+		[1, 3]
+	}
+	#foo: int
+	l6: {
+		#foo: int
+		[1, 3]
+	}
+	n1:  1.0
+	n10: 10
+
+	// t is true
+	t:   true
+	e1:  <1.0
+	e2:  >1.0 & <10
+	e3:  _|_ // e3: index out of range [2] with length 2
+	e4:  _|_ // e4: index 3 out of range
+	e5:  _|_ // e3: index out of range [2] with length 2
+	e6:  false
+	e7:  true
+	e8?: true
+	m1: {
+		// foo is an optional field
+		foo?: 3
+
+		// bar is a field
+		bar: 4
+
+		// baz is a required field.
+		baz!: 5
+	}
+	y1: {
+		src: [1, 2, 3]
+		foo0: 1
+		foo1: 2
+		foo2: 3
+		bar1: 2
+		x: [1, 2, 3]
+		bar2: 3
+	}
+	preserveKeyFieldInComprehension: 1
+	errorStructDef: {
+		a:    1
+		b:    _|_ // errorStructDef.b: conflicting values 2 and 1
+		#Def: 1
+	}
+	errorList: [1, _|_]
+	x: int
+	errorListDef: {
+		#Def: 1
+		[1, _|_]
+	}
+}
+== Eval
+_|_ // e3: index out of range [2] with length 2
+-- diff/-out/value-v3<==>+out/value --
+diff old new
+--- old
++++ new
+@@ -74,11 +74,11 @@
+ 	y1: {
+ 		src: [1, 2, 3]
+ 		foo0: 1
+-		bar1: 2
+-		bar2: 3
+ 		foo1: 2
+-		x: [1, 2, 3]
+ 		foo2: 3
++		bar1: 2
++		x: [1, 2, 3]
++		bar2: 3
+ 	}
+ 	preserveKeyFieldInComprehension: 1
+ 	errorStructDef: {
 -- out/value --
 == Simplified
 _|_ // e3: index out of range [2] with length 2