feat(45679): support 'did you mean' diagnostics for string literal union

src/compiler/checker.ts

@@ -17740,6 +17740,13 @@ namespace ts {
                         message = Diagnostics.Type_0_is_not_assignable_to_type_1_with_exactOptionalPropertyTypes_Colon_true_Consider_adding_undefined_to_the_types_of_the_target_s_properties;
                     }
                     else {
+                        if (source.flags & TypeFlags.StringLiteral && target.flags & TypeFlags.Union) {
+                            const suggestedType = getSuggestedTypeForNonexistentStringLiteralType(source as StringLiteralType, target as UnionType);
+                            if (suggestedType) {
+                                reportError(Diagnostics.Type_0_is_not_assignable_to_type_1_Did_you_mean_2, generalizedSourceType, targetType, typeToString(suggestedType));
+                                return;
+                            }
+                        }
                         message = Diagnostics.Type_0_is_not_assignable_to_type_1;
                     }
                 }
@@ -28127,6 +28134,11 @@ namespace ts {
             return suggestion;
         }
 
+        function getSuggestedTypeForNonexistentStringLiteralType(source: StringLiteralType, target: UnionType): StringLiteralType | undefined {
+            const candidates = target.types.filter((type): type is StringLiteralType => !!(type.flags & TypeFlags.StringLiteral));
+            return getSpellingSuggestion(source.value, candidates, type => type.value);
+        }
+
         /**
          * Given a name and a list of symbols whose names are *not* equal to the name, return a spelling suggestion if there is one that is close enough.
          * Names less than length 3 only check for case-insensitive equality, not levenshtein distance.

src/compiler/diagnosticMessages.json

@@ -3284,6 +3284,10 @@
         "category": "Error",
         "code": 2819
     },
+    "Type '{0}' is not assignable to type '{1}'. Did you mean '{2}'?": {
+        "category": "Error",
+        "code": 2820
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

tests/baselines/reference/didYouMeanStringLiteral.errors.txt

@@ -0,0 +1,20 @@
+tests/cases/compiler/didYouMeanStringLiteral.ts(5,7): error TS2820: Type '"strong"' is not assignable to type 'T1'. Did you mean '"string"'?
+tests/cases/compiler/didYouMeanStringLiteral.ts(6,7): error TS2322: Type '"strong"' is not assignable to type '"number" | "boolean"'.
+tests/cases/compiler/didYouMeanStringLiteral.ts(7,7): error TS2820: Type '"strong"' is not assignable to type '"string" | "boolean"'. Did you mean '"string"'?
+
+
+==== tests/cases/compiler/didYouMeanStringLiteral.ts (3 errors) ====
+    type T1 = "string" | "number" | "boolean";
+    type T2 = T1 & ("number" | "boolean"); // "number" | "boolean"
+    type T3 = T1 & ("string" | "boolean"); // "string" | "boolean"
+
+    const t1: T1 = "strong";
+          ~~
+!!! error TS2820: Type '"strong"' is not assignable to type 'T1'. Did you mean '"string"'?
+    const t2: T2 = "strong";
+          ~~
+!!! error TS2322: Type '"strong"' is not assignable to type '"number" | "boolean"'.
+    const t3: T3 = "strong";
+          ~~
+!!! error TS2820: Type '"strong"' is not assignable to type '"string" | "boolean"'. Did you mean '"string"'?
+

tests/baselines/reference/didYouMeanStringLiteral.js

@@ -0,0 +1,14 @@
+//// [didYouMeanStringLiteral.ts]
+type T1 = "string" | "number" | "boolean";
+type T2 = T1 & ("number" | "boolean"); // "number" | "boolean"
+type T3 = T1 & ("string" | "boolean"); // "string" | "boolean"
+
+const t1: T1 = "strong";
+const t2: T2 = "strong";
+const t3: T3 = "strong";
+
+
+//// [didYouMeanStringLiteral.js]
+var t1 = "strong";
+var t2 = "strong";
+var t3 = "strong";

tests/baselines/reference/didYouMeanStringLiteral.symbols

@@ -0,0 +1,24 @@
+=== tests/cases/compiler/didYouMeanStringLiteral.ts ===
+type T1 = "string" | "number" | "boolean";
+>T1 : Symbol(T1, Decl(didYouMeanStringLiteral.ts, 0, 0))
+
+type T2 = T1 & ("number" | "boolean"); // "number" | "boolean"
+>T2 : Symbol(T2, Decl(didYouMeanStringLiteral.ts, 0, 42))
+>T1 : Symbol(T1, Decl(didYouMeanStringLiteral.ts, 0, 0))
+
+type T3 = T1 & ("string" | "boolean"); // "string" | "boolean"
+>T3 : Symbol(T3, Decl(didYouMeanStringLiteral.ts, 1, 38))
+>T1 : Symbol(T1, Decl(didYouMeanStringLiteral.ts, 0, 0))
+
+const t1: T1 = "strong";
+>t1 : Symbol(t1, Decl(didYouMeanStringLiteral.ts, 4, 5))
+>T1 : Symbol(T1, Decl(didYouMeanStringLiteral.ts, 0, 0))
+
+const t2: T2 = "strong";
+>t2 : Symbol(t2, Decl(didYouMeanStringLiteral.ts, 5, 5))
+>T2 : Symbol(T2, Decl(didYouMeanStringLiteral.ts, 0, 42))
+
+const t3: T3 = "strong";
+>t3 : Symbol(t3, Decl(didYouMeanStringLiteral.ts, 6, 5))
+>T3 : Symbol(T3, Decl(didYouMeanStringLiteral.ts, 1, 38))
+

tests/baselines/reference/didYouMeanStringLiteral.types

@@ -0,0 +1,22 @@
+=== tests/cases/compiler/didYouMeanStringLiteral.ts ===
+type T1 = "string" | "number" | "boolean";
+>T1 : T1
+
+type T2 = T1 & ("number" | "boolean"); // "number" | "boolean"
+>T2 : "number" | "boolean"
+
+type T3 = T1 & ("string" | "boolean"); // "string" | "boolean"
+>T3 : "string" | "boolean"
+
+const t1: T1 = "strong";
+>t1 : T1
+>"strong" : "strong"
+
+const t2: T2 = "strong";
+>t2 : "number" | "boolean"
+>"strong" : "strong"
+
+const t3: T3 = "strong";
+>t3 : "string" | "boolean"
+>"strong" : "strong"
+

tests/baselines/reference/errorsForCallAndAssignmentAreSimilar.errors.txt

@@ -1,5 +1,5 @@
-tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts(11,11): error TS2322: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'.
-tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts(16,11): error TS2322: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'.
+tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts(11,11): error TS2820: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'. Did you mean '"hddvd"'?
+tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts(16,11): error TS2820: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'. Did you mean '"hddvd"'?
 
 
 ==== tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts (2 errors) ====
@@ -15,15 +15,15 @@ tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts(16,11): error TS232
             { kind: "bluray", },
             { kind: "hdpvd", }
               ~~~~
-!!! error TS2322: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'.
+!!! error TS2820: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'. Did you mean '"hddvd"'?
 !!! related TS6500 tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts:3:13: The expected type comes from property 'kind' which is declared here on type 'Disc'
         ]);
 
         const ds: Disc[] = [
             { kind: "bluray", },
             { kind: "hdpvd", }
               ~~~~
-!!! error TS2322: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'.
+!!! error TS2820: Type '"hdpvd"' is not assignable to type '"hddvd" | "bluray"'. Did you mean '"hddvd"'?
 !!! related TS6500 tests/cases/compiler/errorsForCallAndAssignmentAreSimilar.ts:3:13: The expected type comes from property 'kind' which is declared here on type 'Disc'
         ];
     }

tests/cases/compiler/didYouMeanStringLiteral.ts

@@ -0,0 +1,7 @@
+type T1 = "string" | "number" | "boolean";
+type T2 = T1 & ("number" | "boolean"); // "number" | "boolean"
+type T3 = T1 & ("string" | "boolean"); // "string" | "boolean"
+
+const t1: T1 = "strong";
+const t2: T2 = "strong";
+const t3: T3 = "strong";