Report multiple overload errors

src/compiler/core.ts

@@ -600,24 +600,18 @@ namespace ts {
      *
      * @param array The array to flatten.
      */
-    export function flatten<T>(array: ReadonlyArray<T | ReadonlyArray<T> | undefined>): T[];
-    export function flatten<T>(array: ReadonlyArray<T | ReadonlyArray<T> | undefined> | undefined): T[] | undefined;
-    export function flatten<T>(array: ReadonlyArray<T | ReadonlyArray<T> | undefined> | undefined): T[] | undefined {
-        let result: T[] | undefined;
-        if (array) {
-            result = [];
-            for (const v of array) {
-                if (v) {
-                    if (isArray(v)) {
-                        addRange(result, v);
-                    }
-                    else {
-                        result.push(v);
-                    }
+    export function flatten<T>(array: T[][] | ReadonlyArray<T | ReadonlyArray<T> | undefined>): T[] {
+        const result = [];
+        for (const v of array) {
+            if (v) {
+                if (isArray(v)) {
+                    addRange(result, v);
+                }
+                else {
+                    result.push(v);
                 }
             }
         }
-
         return result;
     }
 

src/compiler/diagnosticMessages.json

@@ -2677,6 +2677,22 @@
         "category": "Error",
         "code": 2768
     },
+    "No overload matches this call.": {
+        "category": "Error",
+        "code": 2769
+    },
+    "The last overload gave the following error.": {
+        "category": "Error",
+        "code": 2770
+    },
+    "The last overload is declared here.": {
+        "category": "Error",
+        "code": 2771
+    },
+    "Overload {0} of {1}, '{2}', gave the following error.": {
+        "category": "Error",
+        "code": 2772
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

src/compiler/program.ts

@@ -502,30 +502,29 @@ namespace ts {
         return output;
     }
 
-    export function flattenDiagnosticMessageText(messageText: string | DiagnosticMessageChain | undefined, newLine: string): string {
-        if (isString(messageText)) {
-            return messageText;
+    export function flattenDiagnosticMessageText(diag: string | DiagnosticMessageChain | undefined, newLine: string, indent = 0): string {
+        if (isString(diag)) {
+            return diag;
         }
-        else {
-            let diagnosticChain = messageText;
-            let result = "";
-
-            let indent = 0;
-            while (diagnosticChain) {
-                if (indent) {
-                    result += newLine;
+        else if (diag === undefined) {
+            return "";
+        }
+        let result = "";
+        if (indent) {
+            result += newLine;
 
-                    for (let i = 0; i < indent; i++) {
-                        result += "  ";
-                    }
-                }
-                result += diagnosticChain.messageText;
-                indent++;
-                diagnosticChain = diagnosticChain.next;
+            for (let i = 0; i < indent; i++) {
+                result += "  ";
+            }
+        }
+        result += diag.messageText;
+        indent++;
+        if (diag.next) {
+            for (const kid of diag.next) {
+                result += flattenDiagnosticMessageText(kid, newLine, indent);
             }
-
-            return result;
         }
+        return result;
     }
 
     /* @internal */

src/compiler/types.ts

@@ -4577,7 +4577,7 @@ namespace ts {
         messageText: string;
         category: DiagnosticCategory;
         code: number;
-        next?: DiagnosticMessageChain;
+        next?: DiagnosticMessageChain[];
     }
 
     export interface Diagnostic extends DiagnosticRelatedInformation {

src/compiler/utilities.ts

@@ -7125,8 +7125,8 @@ namespace ts {
         };
     }
 
-    export function chainDiagnosticMessages(details: DiagnosticMessageChain | undefined, message: DiagnosticMessage, ...args: (string | number | undefined)[]): DiagnosticMessageChain;
-    export function chainDiagnosticMessages(details: DiagnosticMessageChain | undefined, message: DiagnosticMessage): DiagnosticMessageChain {
+    export function chainDiagnosticMessages(details: DiagnosticMessageChain | DiagnosticMessageChain[] | undefined, message: DiagnosticMessage, ...args: (string | number | undefined)[]): DiagnosticMessageChain;
+    export function chainDiagnosticMessages(details: DiagnosticMessageChain | DiagnosticMessageChain[] | undefined, message: DiagnosticMessage): DiagnosticMessageChain {
         let text = getLocaleSpecificMessage(message);
 
         if (arguments.length > 2) {
@@ -7138,18 +7138,17 @@ namespace ts {
             category: message.category,
             code: message.code,
 
-            next: details
+            next: details === undefined || Array.isArray(details) ? details : [details]
         };
     }
 
-    export function concatenateDiagnosticMessageChains(headChain: DiagnosticMessageChain, tailChain: DiagnosticMessageChain): DiagnosticMessageChain {
+    export function concatenateDiagnosticMessageChains(headChain: DiagnosticMessageChain, tailChain: DiagnosticMessageChain): void {
         let lastChain = headChain;
         while (lastChain.next) {
-            lastChain = lastChain.next;
+            lastChain = lastChain.next[0];
         }
 
-        lastChain.next = tailChain;
-        return headChain;
+        lastChain.next = [tailChain];
     }
 
     function getDiagnosticFilePath(diagnostic: Diagnostic): string | undefined {
@@ -7185,29 +7184,42 @@ namespace ts {
     }
 
     function compareMessageText(t1: string | DiagnosticMessageChain, t2: string | DiagnosticMessageChain): Comparison {
-        let text1: string | DiagnosticMessageChain | undefined = t1;
-        let text2: string | DiagnosticMessageChain | undefined = t2;
-        while (text1 && text2) {
-            // We still have both chains.
-            const string1 = isString(text1) ? text1 : text1.messageText;
-            const string2 = isString(text2) ? text2 : text2.messageText;
-
-            const res = compareStringsCaseSensitive(string1, string2);
+        if (typeof t1 === "string" && typeof t2 === "string") {
+            return compareStringsCaseSensitive(t1, t2);
+        }
+        else if (typeof t1 === "string") {
+            return Comparison.LessThan;
+        }
+        else if (typeof t2 === "string") {
+            return Comparison.GreaterThan;
+        }
+        let res = compareStringsCaseSensitive(t1.messageText, t2.messageText);
+        if (res) {
+            return res;
+        }
+        if (!t1.next && !t2.next) {
+            return Comparison.EqualTo;
+        }
+        if (!t1.next) {
+            return Comparison.LessThan;
+        }
+        if (!t2.next) {
+            return Comparison.GreaterThan;
+        }
+        const len = Math.min(t1.next.length, t2.next.length);
+        for (let i = 0; i < len; i++) {
+            res = compareMessageText(t1.next[i], t2.next[i]);
             if (res) {
                 return res;
             }
-
-            text1 = isString(text1) ? undefined : text1.next;
-            text2 = isString(text2) ? undefined : text2.next;
         }
-
-        if (!text1 && !text2) {
-            // if the chains are done, then these messages are the same.
-            return Comparison.EqualTo;
+        if (t1.next.length < t2.next.length) {
+            return Comparison.LessThan;
         }
-
-        // We still have one chain remaining.  The shorter chain should come first.
-        return text1 ? Comparison.GreaterThan : Comparison.LessThan;
+        else if (t1.next.length > t2.next.length) {
+            return Comparison.GreaterThan;
+        }
+        return Comparison.EqualTo;
     }
 
     export function getEmitScriptTarget(compilerOptions: CompilerOptions) {
@@ -8105,7 +8117,7 @@ namespace ts {
             visitDirectory(basePath, combinePaths(currentDirectory, basePath), depth);
         }
 
-        return flatten<string>(results);
+        return flatten(results);
 
         function visitDirectory(path: string, absolutePath: string, depth: number | undefined) {
             const canonicalPath = toCanonical(realpath(absolutePath));

src/harness/fourslash.ts

@@ -1497,13 +1497,7 @@ Actual: ${stringify(fullActual)}`);
                     const diagnostics = ts.getPreEmitDiagnostics(this.languageService.getProgram()!); // TODO: GH#18217
                     for (const diagnostic of diagnostics) {
                         if (!ts.isString(diagnostic.messageText)) {
-                            let chainedMessage: ts.DiagnosticMessageChain | undefined = diagnostic.messageText;
-                            let indentation = " ";
-                            while (chainedMessage) {
-                                resultString += indentation + chainedMessage.messageText + Harness.IO.newLine();
-                                chainedMessage = chainedMessage.next;
-                                indentation = indentation + " ";
-                            }
+                            resultString += this.flattenChainedMessage(diagnostic.messageText);
                         }
                         else {
                             resultString += "  " + diagnostic.messageText + Harness.IO.newLine();
@@ -1521,6 +1515,17 @@ Actual: ${stringify(fullActual)}`);
             Harness.Baseline.runBaseline(ts.Debug.assertDefined(this.testData.globalOptions[MetadataOptionNames.baselineFile]), resultString);
         }
 
+        private flattenChainedMessage(diag: ts.DiagnosticMessageChain, indent = " ") {
+            let result = "";
+            result += indent + diag.messageText + Harness.IO.newLine();
+            if (diag.next) {
+                for (const kid of diag.next) {
+                    result += this.flattenChainedMessage(kid, indent + " ");
+                }
+            }
+            return result;
+        }
+
         public baselineQuickInfo() {
             const baselineFile = this.getBaselineFileName();
             Harness.Baseline.runBaseline(

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2457,7 +2457,7 @@ declare namespace ts {
         messageText: string;
         category: DiagnosticCategory;
         code: number;
-        next?: DiagnosticMessageChain;
+        next?: DiagnosticMessageChain[];
     }
     interface Diagnostic extends DiagnosticRelatedInformation {
         /** May store more in future. For now, this will simply be `true` to indicate when a diagnostic is an unused-identifier diagnostic. */
@@ -4277,7 +4277,7 @@ declare namespace ts {
     function formatDiagnostics(diagnostics: ReadonlyArray<Diagnostic>, host: FormatDiagnosticsHost): string;
     function formatDiagnostic(diagnostic: Diagnostic, host: FormatDiagnosticsHost): string;
     function formatDiagnosticsWithColorAndContext(diagnostics: ReadonlyArray<Diagnostic>, host: FormatDiagnosticsHost): string;
-    function flattenDiagnosticMessageText(messageText: string | DiagnosticMessageChain | undefined, newLine: string): string;
+    function flattenDiagnosticMessageText(diag: string | DiagnosticMessageChain | undefined, newLine: string, indent?: number): string;
     function getConfigFileParsingDiagnostics(configFileParseResult: ParsedCommandLine): ReadonlyArray<Diagnostic>;
     /**
      * Create a new 'Program' instance. A Program is an immutable collection of 'SourceFile's and a 'CompilerOptions'

tests/baselines/reference/api/typescript.d.ts

@@ -2457,7 +2457,7 @@ declare namespace ts {
         messageText: string;
         category: DiagnosticCategory;
         code: number;
-        next?: DiagnosticMessageChain;
+        next?: DiagnosticMessageChain[];
     }
     interface Diagnostic extends DiagnosticRelatedInformation {
         /** May store more in future. For now, this will simply be `true` to indicate when a diagnostic is an unused-identifier diagnostic. */
@@ -4277,7 +4277,7 @@ declare namespace ts {
     function formatDiagnostics(diagnostics: ReadonlyArray<Diagnostic>, host: FormatDiagnosticsHost): string;
     function formatDiagnostic(diagnostic: Diagnostic, host: FormatDiagnosticsHost): string;
     function formatDiagnosticsWithColorAndContext(diagnostics: ReadonlyArray<Diagnostic>, host: FormatDiagnosticsHost): string;
-    function flattenDiagnosticMessageText(messageText: string | DiagnosticMessageChain | undefined, newLine: string): string;
+    function flattenDiagnosticMessageText(diag: string | DiagnosticMessageChain | undefined, newLine: string, indent?: number): string;
     function getConfigFileParsingDiagnostics(configFileParseResult: ParsedCommandLine): ReadonlyArray<Diagnostic>;
     /**
      * Create a new 'Program' instance. A Program is an immutable collection of 'SourceFile's and a 'CompilerOptions'