internal/core/eval: centralize type checking

This aims to make error checking more correct, easier
to manage and improve error messages.

Change-Id: I00bfd0742bb90549679eaa63894c30b1092a228d
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/6702
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

cue/testdata/basicrewrite/001_regexp.txtar

@@ -62,7 +62,7 @@ e3: _|_ // conflicting values !="a" and <5 (mismatched types string and number)
 }
 -- out/eval --
 Errors:
-e3: invalid value <5 (mismatched types number and string)
+e3: conflicting values !="a" and <5 (mismatched types string and number)
 b3: invalid value "foo" (out of bound =~"[a-z]{4}"):
     ./in.cue:10:5
 e1: cannot use 1 (type int) as type (string|bytes):
@@ -95,6 +95,6 @@ Result:
     //     ./in.cue:19:5
   }
   e3: (_|_){
-    // [eval] e3: invalid value <5 (mismatched types number and string)
+    // [eval] e3: conflicting values !="a" and <5 (mismatched types string and number)
   }
 }

cue/testdata/basicrewrite/006_basic_type.txtar

@@ -34,7 +34,7 @@ f: true
 }
 -- out/eval --
 Errors:
-d: invalid value float (mismatched types float and int)
+d: conflicting values int and float (mismatched types int and float)
 
 Result:
 (_|_){
@@ -43,7 +43,7 @@ Result:
   b: (int){ 1 }
   c: (float){ 1.0 }
   d: (_|_){
-    // [eval] d: invalid value float (mismatched types float and int)
+    // [eval] d: conflicting values int and float (mismatched types int and float)
   }
   e: (string){ "4" }
   f: (bool){ true }

cue/testdata/basicrewrite/010_lists.txtar

@@ -76,7 +76,7 @@ e5: [1, 2, 4, _|_, // invalid value 8 (out of bound <=5)
 }
 -- out/eval --
 Errors:
-e: conflicting types list and int
+e: conflicting values 4 and [] (mismatched types int and list)
 e2: invalid list index d (type string):
     ./in.cue:5:12
 e3: invalid negative index -1:
@@ -101,7 +101,7 @@ Result:
     2: (int){ 3 }
   }
   e: (_|_){
-    // [eval] e: conflicting types list and int
+    // [eval] e: conflicting values 4 and [] (mismatched types int and list)
   }
   e2: (_|_){
     // [eval] e2: invalid list index d (type string):

cue/testdata/basicrewrite/013_obj_unify.txtar

@@ -75,7 +75,7 @@ e: _|_ // conflicting values 1 and {a: 3} (mismatched types int and struct)
 }
 -- out/eval --
 Errors:
-e: conflicting values struct and int
+e: conflicting values 1 and {a:3} (mismatched types int and struct)
 
 Result:
 (_|_){
@@ -97,7 +97,7 @@ Result:
     b: (int){ 2 }
   }
   e: (_|_){
-    // [eval] e: conflicting values struct and int
+    // [eval] e: conflicting values 1 and {a:3} (mismatched types int and struct)
     a: (int){ 3 }
   }
 }

cue/testdata/basicrewrite/015_types.txtar

@@ -39,13 +39,13 @@ m:  _|_ // invalid operation -false (- bool)
 }
 -- out/eval --
 Errors:
-e: invalid value string (mismatched types string and int)
-e2: invalid value string (mismatched types string and int)
+e: conflicting values int and string (mismatched types int and string)
+e2: conflicting values 1 and string (mismatched types int and string)
 b: value can never become concrete:
     ./in.cue:7:5
-p: invalid operation ++true (+ bool):
+p: invalid operation +true (+ bool):
     ./in.cue:8:5
-m: invalid operation --false (- bool):
+m: invalid operation -false (- bool):
     ./in.cue:9:5
 
 Result:
@@ -56,21 +56,21 @@ Result:
   s: (string){ string }
   t: (string){ "s" }
   e: (_|_){
-    // [eval] e: invalid value string (mismatched types string and int)
+    // [eval] e: conflicting values int and string (mismatched types int and string)
   }
   e2: (_|_){
-    // [eval] e2: invalid value string (mismatched types string and int)
+    // [eval] e2: conflicting values 1 and string (mismatched types int and string)
   }
   b: (_|_){
     // [eval] b: value can never become concrete:
     //     ./in.cue:7:5
   }
   p: (_|_){
-    // [eval] p: invalid operation ++true (+ bool):
+    // [eval] p: invalid operation +true (+ bool):
     //     ./in.cue:8:5
   }
   m: (_|_){
-    // [eval] m: invalid operation --false (- bool):
+    // [eval] m: invalid operation -false (- bool):
     //     ./in.cue:9:5
   }
 }

cue/testdata/cycle/structural.txtar

@@ -220,7 +220,7 @@ Errors:
 a1.f.0: structural cycle
 a3.f.g: structural cycle
 b4.x.y.0: structural cycle
-b6.b.a.0: conflicting types list and int
+b6.b.a.0: conflicting values 1 and [1] (mismatched types int and list)
 b6.b.a.0.0: structural cycle
 b6.x.a.0: structural cycle
 b7.a.0: structural cycle
@@ -234,16 +234,18 @@ e1.a.c: structural cycle
 e1.b.c: structural cycle
 e2.a.c: structural cycle
 e2.b.c: structural cycle
-e3.a: conflicting types list and struct
-e3.a.0: conflicting types list and struct
+e3.a: conflicting values [a] and {c:a} (mismatched types list and struct)
+e3.a.0: conflicting values [a] and {c:a} (mismatched types list and struct)
 e3.a.0: structural cycle
-e3.a.c: conflicting types list and struct
+e3.a.c: conflicting values [a] and {c:a} (mismatched types list and struct)
 e3.a.c: structural cycle
-e3.b: conflicting types list and struct
-e3.b.0: conflicting types list and struct
+e3.b: conflicting values [b] and {c:b} (mismatched types list and struct)
+e3.b.0: conflicting values [b] and {c:b} (mismatched types list and struct)
 e3.b.0: structural cycle
-e3.b.c: conflicting types list and struct
+e3.b.c: conflicting values [b] and {c:b} (mismatched types list and struct)
 e3.b.c: structural cycle
+e4.a.0: conflicting values [{c:1}] and {} (mismatched types list and struct)
+e4.b.0: conflicting values [{c:1}] and {} (mismatched types list and struct)
 z1.z.f.h.h: structural cycle
 z1.z.g.h: structural cycle
 b4.x.y.0: structural cycle:
@@ -362,7 +364,7 @@ Result:
       a: (_|_){
         // [eval]
         0: (_|_){
-          // [eval] b6.b.a.0: conflicting types list and int
+          // [eval] b6.b.a.0: conflicting values 1 and [1] (mismatched types int and list)
           0: (_|_){
             // [structural cycle] b6.b.a.0.0: structural cycle
           }
@@ -570,17 +572,17 @@ Result:
   e3: (_|_){
     // [eval]
     a: (_|_){
-      // [eval] e3.a: conflicting types list and struct
+      // [eval] e3.a: conflicting values [a] and {c:a} (mismatched types list and struct)
       c: (_|_){
-        // [eval] e3.a.c: conflicting types list and struct
+        // [eval] e3.a.c: conflicting values [a] and {c:a} (mismatched types list and struct)
         // e3.a.c: structural cycle
         c: (_|_){// 〈1;a〉
         }
         0: (_|_){// 〈0;a〉
         }
       }
       0: (_|_){
-        // [eval] e3.a.0: conflicting types list and struct
+        // [eval] e3.a.0: conflicting values [a] and {c:a} (mismatched types list and struct)
         // e3.a.0: structural cycle
         c: (_|_){// 〈1;a〉
         }
@@ -589,17 +591,17 @@ Result:
       }
     }
     b: (_|_){
-      // [eval] e3.b: conflicting types list and struct
+      // [eval] e3.b: conflicting values [b] and {c:b} (mismatched types list and struct)
       c: (_|_){
-        // [eval] e3.b.c: conflicting types list and struct
+        // [eval] e3.b.c: conflicting values [b] and {c:b} (mismatched types list and struct)
         // e3.b.c: structural cycle
         c: (_|_){// 〈1;b〉
         }
         0: (_|_){// 〈0;b〉
         }
       }
       0: (_|_){
-        // [eval] e3.b.0: conflicting types list and struct
+        // [eval] e3.b.0: conflicting values [b] and {c:b} (mismatched types list and struct)
         // e3.b.0: structural cycle
         c: (_|_){// 〈1;b〉
         }
@@ -608,16 +610,21 @@ Result:
       }
     }
   }
-  e4: (struct){
-    a: (#list){
-      0: (#list){
+  e4: (_|_){
+    // [eval]
+    a: (_|_){
+      // [eval]
+      0: (_|_){
+        // [eval] e4.a.0: conflicting values [{c:1}] and {} (mismatched types list and struct)
         0: (struct){
           c: (int){ 1 }
         }
       }
     }
-    b: (#list){
-      0: (#list){
+    b: (_|_){
+      // [eval]
+      0: (_|_){
+        // [eval] e4.b.0: conflicting values [{c:1}] and {} (mismatched types list and struct)
         0: (struct){
           c: (int){ 1 }
         }