internal/core/adt: handle yields in Resolve

In some cases, Resolve will invoke a "yield".
As this is not within usual evaluation, this
must be explicitly handled. We simply
convert it to an error.

Fixes #3972

Signed-off-by: Marcel van Lohuizen <[email protected]>
Change-Id: I460038a84ea7b8f4ce0e96ca91eccbe44e05a631
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1217127
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Daniel Martí <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

Author: mpvl

cue/testdata/builtins/export.txtar

@@ -33,63 +33,6 @@ Disjuncts:    12
 
 CloseIDElems: 0
 NumCloseIDs: 2
--- out/evalalpha --
-Errors:
-issue3972.output.out1: error in call to encoding/yaml.Marshal: BUG: non-stringifiable *adt.scheduler:
-    ./in.cue:19:16
-
-Result:
-(_|_){
-  // [eval]
-  issue3972: (_|_){
-    // [eval]
-    output: (_|_){
-      // [eval]
-      out0: (string){ "static" }
-      out1: (_|_){
-        // [eval] issue3972.output.out1: error in call to encoding/yaml.Marshal: BUG: non-stringifiable *adt.scheduler:
-        //     ./in.cue:19:16
-      }
-    }
-    input: (struct){
-      inputStatic: (string){ "static" }
-    }
-    derived: (struct){
-      derivedStatic: (string){ "static" }
-    }
-    _out1: (#list){
-      0: (string){ "derivedStatic" }
-    }
-  }
-}
--- diff/-out/evalalpha<==>+out/eval --
-diff old new
---- old
-+++ new
-@@ -1,8 +1,19 @@
--(struct){
--  issue3972: (struct){
--    output: (struct){
-+Errors:
-+issue3972.output.out1: error in call to encoding/yaml.Marshal: BUG: non-stringifiable *adt.scheduler:
-+    ./in.cue:19:16
-+
-+Result:
-+(_|_){
-+  // [eval]
-+  issue3972: (_|_){
-+    // [eval]
-+    output: (_|_){
-+      // [eval]
-       out0: (string){ "static" }
--      out1: (string){ "- derivedStatic\n" }
-+      out1: (_|_){
-+        // [eval] issue3972.output.out1: error in call to encoding/yaml.Marshal: BUG: non-stringifiable *adt.scheduler:
-+        //     ./in.cue:19:16
-+      }
-     }
-     input: (struct){
-       inputStatic: (string){ "static" }
 -- out/eval --
 (struct){
   issue3972: (struct){

internal/core/adt/context.go

@@ -418,7 +418,17 @@ func (c *OpContext) PopArcAndLabel(saved *Vertex) {
 //
 // Should only be used to insert Conjuncts. TODO: perhaps only return Conjuncts
 // and error.
-func (c *OpContext) Resolve(x Conjunct, r Resolver) (*Vertex, *Bottom) {
+func (c *OpContext) Resolve(x Conjunct, r Resolver) (v *Vertex, b *Bottom) {
+	defer func() {
+		x := recover()
+		switch x.(type) {
+		case nil:
+		case *scheduler:
+			b = c.NewErrf("unresolved value %s", r)
+		default:
+			panic(x)
+		}
+	}()
 	return c.resolveState(x, r, final(finalized, allKnown))
 }