add related error span for default exports

Author: Kingwl

src/compiler/binder.ts

@@ -410,7 +410,11 @@ namespace ts {
                         forEach(symbol.declarations, declaration => {
                             file.bindDiagnostics.push(createDiagnosticForNode(getNameOfDeclaration(declaration) || declaration, message, getDisplayName(declaration)));
                         });
-                        file.bindDiagnostics.push(createDiagnosticForNode(getNameOfDeclaration(node) || node, message, getDisplayName(node)));
+                        const declarationName = getNameOfDeclaration(node) || node;
+                        const diag = createDiagnosticForNode(declarationName, message, getDisplayName(node))
+                        file.bindDiagnostics.push(
+                            isDefaultExport ? addRelatedInfo( diag, createDiagnosticForNode(declarationName, Diagnostics.This_export_conflicts_with_the_first)) : diag
+                        );
 
                         symbol = createSymbol(SymbolFlags.None, name);
                     }

src/compiler/checker.ts

@@ -708,14 +708,6 @@ namespace ts {
             }
         }
 
-        function addRelatedInfo(diagnostic: Diagnostic, ...relatedInformation: DiagnosticRelatedInformation[]) {
-            if (!diagnostic.relatedInformation) {
-                diagnostic.relatedInformation = [];
-            }
-            diagnostic.relatedInformation.push(...relatedInformation);
-            return diagnostic;
-        }
-
         function error(location: Node | undefined, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): Diagnostic {
             const diagnostic = location
                 ? createDiagnosticForNode(location, message, arg0, arg1, arg2, arg3)

src/compiler/diagnosticMessages.json

@@ -2401,6 +2401,10 @@
         "category": "Error",
         "code": 2728
     },
+    "This export conflicts with the first.": {
+        "category": "Error",
+        "code": 2729
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

src/compiler/utilities.ts

@@ -8106,4 +8106,12 @@ namespace ts {
 
         return findBestPatternMatch(patterns, _ => _, candidate);
     }
+
+    export function addRelatedInfo<T extends Diagnostic>(diagnostic: T, ...relatedInformation: DiagnosticRelatedInformation[]): T {
+        if (!diagnostic.relatedInformation) {
+            diagnostic.relatedInformation = [];
+        }
+        diagnostic.relatedInformation.push(...relatedInformation);
+        return diagnostic;
+    }
 }