Issue a diagnostic when the node builder performs truncation despite the NoTruncation flag being set (#40477)

src/compiler/checker.ts

@@ -4311,6 +4311,9 @@ namespace ts {
                     approximateLength: 0
                 };
                 const resultingNode = cb(context);
+                if (context.truncating && context.flags & NodeBuilderFlags.NoTruncation) {
+                    context.tracker?.reportTruncationError?.();
+                }
                 return context.encounteredError ? undefined : resultingNode;
             }
 

src/compiler/diagnosticMessages.json

@@ -4920,6 +4920,10 @@
         "category": "Error",
         "code": 7055
     },
+    "The inferred type of this node exceeds the maximum length the compiler will serialize. An explicit type annotation is needed.": {
+        "category": "Error",
+        "code": 7056
+    },
 
     "You cannot rename this element.": {
         "category": "Error",

src/compiler/transformers/declarations.ts

@@ -73,6 +73,7 @@ namespace ts {
             reportCyclicStructureError,
             reportPrivateInBaseOfClassExpression,
             reportLikelyUnsafeImportRequiredError,
+            reportTruncationError,
             moduleResolverHost: host,
             trackReferencedAmbientModule,
             trackExternalModuleSymbolOfImportTypeNode,
@@ -197,6 +198,12 @@ namespace ts {
             }
         }
 
+        function reportTruncationError() {
+            if (errorNameNode) {
+                context.addDiagnostic(createDiagnosticForNode(errorNameNode, Diagnostics.The_inferred_type_of_this_node_exceeds_the_maximum_length_the_compiler_will_serialize_An_explicit_type_annotation_is_needed));
+            }
+        }
+
         function reportNonlocalAugmentation(containingFile: SourceFile, parentSymbol: Symbol, symbol: Symbol) {
             const primaryDeclaration = find(parentSymbol.declarations, d => getSourceFileOfNode(d) === containingFile)!;
             const augmentingDeclarations = filter(symbol.declarations, d => getSourceFileOfNode(d) !== containingFile);

src/compiler/types.ts

@@ -7867,6 +7867,7 @@ namespace ts {
         reportInaccessibleUniqueSymbolError?(): void;
         reportCyclicStructureError?(): void;
         reportLikelyUnsafeImportRequiredError?(specifier: string): void;
+        reportTruncationError?(): void;
         moduleResolverHost?: ModuleSpecifierResolutionHost & { getCommonSourceDirectory(): string };
         trackReferencedAmbientModule?(decl: ModuleDeclaration, symbol: Symbol): void;
         trackExternalModuleSymbolOfImportTypeNode?(symbol: Symbol): void;

tests/baselines/reference/hugeDeclarationOutputGetsTruncatedWithError.errors.txt

@@ -0,0 +1,11 @@
+tests/cases/compiler/hugeDeclarationOutputGetsTruncatedWithError.ts(5,14): error TS7056: The inferred type of this node exceeds the maximum length the compiler will serialize. An explicit type annotation is needed.
+
+
+==== tests/cases/compiler/hugeDeclarationOutputGetsTruncatedWithError.ts (1 errors) ====
+    type props = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z";
+    
+    type manyprops = `${props}${props}`;
+    
+    export const c = null as any as {[K in manyprops]: {[K2 in manyprops]: `${K}.${K2}`}};
+                 ~
+!!! error TS7056: The inferred type of this node exceeds the maximum length the compiler will serialize. An explicit type annotation is needed.

tests/baselines/reference/hugeDeclarationOutputGetsTruncatedWithError.js

@@ -0,0 +1,12 @@
+//// [hugeDeclarationOutputGetsTruncatedWithError.ts]
+type props = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z";
+
+type manyprops = `${props}${props}`;
+
+export const c = null as any as {[K in manyprops]: {[K2 in manyprops]: `${K}.${K2}`}};
+
+//// [hugeDeclarationOutputGetsTruncatedWithError.js]
+"use strict";
+exports.__esModule = true;
+exports.c = void 0;
+exports.c = null;

tests/baselines/reference/hugeDeclarationOutputGetsTruncatedWithError.symbols

@@ -0,0 +1,18 @@
+=== tests/cases/compiler/hugeDeclarationOutputGetsTruncatedWithError.ts ===
+type props = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z";
+>props : Symbol(props, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 0, 0))
+
+type manyprops = `${props}${props}`;
+>manyprops : Symbol(manyprops, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 0, 167))
+>props : Symbol(props, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 0, 0))
+>props : Symbol(props, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 0, 0))
+
+export const c = null as any as {[K in manyprops]: {[K2 in manyprops]: `${K}.${K2}`}};
+>c : Symbol(c, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 4, 12))
+>K : Symbol(K, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 4, 34))
+>manyprops : Symbol(manyprops, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 0, 167))
+>K2 : Symbol(K2, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 4, 53))
+>manyprops : Symbol(manyprops, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 0, 167))
+>K : Symbol(K, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 4, 34))
+>K2 : Symbol(K2, Decl(hugeDeclarationOutputGetsTruncatedWithError.ts, 4, 53))
+

tests/cases/compiler/hugeDeclarationOutputGetsTruncatedWithError.ts

@@ -0,0 +1,6 @@
+// @declaration: true
+type props = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z";
+
+type manyprops = `${props}${props}`;
+
+export const c = null as any as {[K in manyprops]: {[K2 in manyprops]: `${K}.${K2}`}};