internal/core/compile: better error message for user-defined errors

Fixes #321

Change-Id: I0a04fd56a132a98ae3f143e91c4c185052cee4d7
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/7069
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>

cue/testdata/basicrewrite/000_errors.txtar

@@ -9,38 +9,38 @@ c: b.a == _|_
 d: _|_ != b.a
 e: _|_ == _|_
 -- out/def --
-a: _|_ // from source
-b: _|_ // from source
+a: _|_ // explicit error (_|_ literal) in source
+b: _|_ // explicit error (_|_ literal) in source
 c: true
 d: false
 e: true
 -- out/legacy-debug --
-<0>{a: _|_(from source), b: _|_(from source), c: true, d: false, e: true}
+<0>{a: _|_(explicit error (_|_ literal) in source), b: _|_(explicit error (_|_ literal) in source), c: true, d: false, e: true}
 -- out/compile --
 --- in.cue
 {
-  a: (_|_(from source) & _|_(from source))
-  b: (null & _|_(from source))
-  c: (〈0;b〉.a == _|_(from source))
-  d: (_|_(from source) != 〈0;b〉.a)
-  e: (_|_(from source) == _|_(from source))
+  a: (_|_(explicit error (_|_ literal) in source) & _|_(explicit error (_|_ literal) in source))
+  b: (null & _|_(explicit error (_|_ literal) in source))
+  c: (〈0;b〉.a == _|_(explicit error (_|_ literal) in source))
+  d: (_|_(explicit error (_|_ literal) in source) != 〈0;b〉.a)
+  e: (_|_(explicit error (_|_ literal) in source) == _|_(explicit error (_|_ literal) in source))
 }
 -- out/eval --
 Errors:
-from source:
+explicit error (_|_ literal) in source:
     ./in.cue:1:4
-from source:
+explicit error (_|_ literal) in source:
     ./in.cue:2:11
 
 Result:
 (_|_){
   // [user]
   a: (_|_){
-    // [user] from source:
+    // [user] explicit error (_|_ literal) in source:
     //     ./in.cue:1:4
   }
   b: (_|_){
-    // [user] from source:
+    // [user] explicit error (_|_ literal) in source:
     //     ./in.cue:2:11
   }
   c: (bool){ true }

cue/testdata/comprehensions/issue287.txtar

@@ -18,12 +18,12 @@ if #E["y"] != _|_ {
 -- out/compile --
 --- in.cue
 {
-  if (〈0;#E〉["x"] != _|_(from source)) {
+  if (〈0;#E〉["x"] != _|_(explicit error (_|_ literal) in source)) {
     #E: {
       y: true
     }
   }
-  if (〈0;#E〉["y"] != _|_(from source)) {
+  if (〈0;#E〉["y"] != _|_(explicit error (_|_ literal) in source)) {
     z: true
   }
   #E: {

cue/testdata/eval/errunifiy.txtar

@@ -9,15 +9,15 @@ b: "t"
 
 -- out/eval --
 Errors:
-from source:
+explicit error (_|_ literal) in source:
     ./in.cue:4:4
 
 Result:
 (_|_){
   // [user]
   a: (string){ "t" }
   b: (_|_){
-    // [user] from source:
+    // [user] explicit error (_|_ literal) in source:
     //     ./in.cue:4:4
   }
 }
@@ -26,6 +26,6 @@ Result:
 {
   a: or([])
   a: "t"
-  b: _|_(from source)
+  b: _|_(explicit error (_|_ literal) in source)
   b: "t"
 }

cue/testdata/fulleval/031_comparison_against_bottom.txtar

@@ -32,27 +32,27 @@ i: false
 -- out/compile --
 --- in.cue
 {
-  a: (_|_(from source) == _|_(from source))
+  a: (_|_(explicit error (_|_ literal) in source) == _|_(explicit error (_|_ literal) in source))
   b: ((〈0;err〉 == 1) & 2)
-  c: (〈0;err〉 == _|_(from source))
-  d: (〈0;err〉 != _|_(from source))
+  c: (〈0;err〉 == _|_(explicit error (_|_ literal) in source))
+  d: (〈0;err〉 != _|_(explicit error (_|_ literal) in source))
   e: ((〈0;err〉 != 1) & 3)
   f: (({
     a: 1
   } & {
     a: 2
-  }) == _|_(from source))
+  }) == _|_(explicit error (_|_ literal) in source))
   g: (({
     a: 1
   } & {
     b: 2
-  }) == _|_(from source))
-  h: (_|_(from source) == ({
+  }) == _|_(explicit error (_|_ literal) in source))
+  h: (_|_(explicit error (_|_ literal) in source) == ({
     a: 1
   } & {
     a: 2
   }))
-  i: (_|_(from source) == ({
+  i: (_|_(explicit error (_|_ literal) in source) == ({
     a: 1
   } & {
     b: 2

cue/types_test.go

@@ -269,8 +269,8 @@ func TestInt(t *testing.T) {
 		notInt: true,
 	}, {
 		value:  "_|_",
-		err:    "from source",
-		errU:   "from source",
+		err:    "explicit error (_|_ literal) in source",
+		errU:   "explicit error (_|_ literal) in source",
 		notInt: true,
 	}}
 	for _, tc := range testCases {
@@ -485,7 +485,7 @@ func TestError(t *testing.T) {
 		err   string
 	}{{
 		value: `_|_`,
-		err:   "from source",
+		err:   "explicit error (_|_ literal) in source",
 	}, {
 		value: `"Hello world!"`,
 	}, {
@@ -506,7 +506,7 @@ func TestNull(t *testing.T) {
 		err   string
 	}{{
 		value: `v: _|_`,
-		err:   "from source",
+		err:   "explicit error (_|_ literal) in source",
 	}, {
 		value: `v: "str"`,
 		err:   "cannot use value \"str\" (type string) as null",
@@ -531,7 +531,7 @@ func TestBool(t *testing.T) {
 		err   string
 	}{{
 		value: `_|_`,
-		err:   "from source",
+		err:   "explicit error (_|_ literal) in source",
 	}, {
 		value: `"str"`,
 		err:   "cannot use value \"str\" (type string) as bool",
@@ -563,7 +563,7 @@ func TestList(t *testing.T) {
 		err   string
 	}{{
 		value: `_|_`,
-		err:   "from source",
+		err:   "explicit error (_|_ literal) in source",
 	}, {
 		value: `"str"`,
 		err:   "cannot use value \"str\" (type string) as list",
@@ -614,7 +614,7 @@ func TestFields(t *testing.T) {
 		res:   "{reg:4,}",
 	}, {
 		value: `_|_`,
-		err:   "from source",
+		err:   "explicit error (_|_ literal) in source",
 	}, {
 		value: `"str"`,
 		err:   "cannot use value \"str\" (type string) as struct",
@@ -1324,7 +1324,7 @@ func TestDecode(t *testing.T) {
 		err   string
 	}{{
 		value: `_|_`,
-		err:   "from source",
+		err:   "explicit error (_|_ literal) in source",
 	}, {
 		value: `"str"`,
 		dst:   new(string),
@@ -1607,11 +1607,11 @@ func TestValueLookup(t *testing.T) {
 	}{{
 		config: "_|_",
 		path:   strList(""),
-		str:    "from source",
+		str:    "explicit error (_|_ literal) in source",
 	}, {
 		config: "_|_",
 		path:   strList("a"),
-		str:    "from source",
+		str:    "explicit error (_|_ literal) in source",
 	}, {
 		config: config,
 		path:   strList(),
@@ -2107,7 +2107,7 @@ func TestMarshalJSON(t *testing.T) {
 		json:  `null`,
 	}, {
 		value: `_|_`,
-		err:   "from source",
+		err:   "explicit error (_|_ literal) in source",
 	}, {
 		value: `(a.b)
 		a: {}`,
@@ -2272,7 +2272,7 @@ func TestWalk(t *testing.T) {
 		out:   `null`,
 	}, {
 		value: `_|_`,
-		out:   "_|_(from source)",
+		out:   "_|_(explicit error (_|_ literal) in source)",
 	}, {
 		value: `(a.b)
 			a: {}`,

internal/core/compile/compile.go

@@ -778,7 +778,7 @@ func (c *compiler) expr(expr ast.Expr) adt.Expr {
 		return &adt.Bottom{
 			Src:  n,
 			Code: adt.UserError,
-			Err:  errors.Newf(n.Pos(), "from source"),
+			Err:  errors.Newf(n.Pos(), "explicit error (_|_ literal) in source"),
 		}
 
 	case *ast.BadExpr: