Use 'approximation' instead of 'approximate'.

src/services/services.ts

@@ -1587,7 +1587,9 @@ namespace ts {
                     kind: ScriptElementKind.unknown,
                     kindModifiers: ScriptElementKindModifier.none,
                     textSpan: createTextSpanFromNode(nodeForQuickInfo, sourceFile),
-                    displayParts: typeChecker.runWithCancellationToken(cancellationToken, typeChecker => typeToDisplayParts(typeChecker, type, getContainerNode(nodeForQuickInfo))),
+                    displayParts: prefixWithApproximation(
+                        typeChecker.runWithCancellationToken(cancellationToken, typeChecker => typeToDisplayParts(typeChecker, type, getContainerNode(nodeForQuickInfo)))
+                    ),
                     documentation: type.symbol ? type.symbol.getDocumentationComment(typeChecker) : undefined,
                     tags: type.symbol ? type.symbol.getJsDocTags() : undefined
                 };
@@ -1600,7 +1602,7 @@ namespace ts {
                 kind: symbolKind,
                 kindModifiers: SymbolDisplay.getSymbolModifiers(symbol),
                 textSpan: createTextSpanFromNode(nodeForQuickInfo, sourceFile),
-                displayParts,
+                displayParts: prefixWithApproximation(displayParts),
                 documentation,
                 tags,
             };
@@ -1630,6 +1632,13 @@ namespace ts {
             }
         }
 
+        function prefixWithApproximation(displayParts: SymbolDisplayPart[]): SymbolDisplayPart[] {
+            if (languageServiceMode === LanguageServiceMode.Semantic) {
+                return displayParts;
+            }
+            return [textPart("(approximation)"), spacePart(), ...displayParts];
+        }
+
         /// Goto definition
         function getDefinitionAtPosition(fileName: string, position: number): readonly DefinitionInfo[] | undefined {
             synchronizeHostData();

src/testRunner/unittests/tsserver/partialSemanticServer.ts

@@ -30,6 +30,22 @@ import { something } from "something";
             return { host, session, file1, file2, file3, something, configFile };
         }
 
+        it("adds '(approximation)' to the description of quick info", () => {
+            const file: File = {
+                path: `${tscWatch.projectRoot}/foo.ts`,
+                content: "export const foo = 100;"
+            };
+            const host = createServerHost([file]);
+            const session = createSession(host, { serverMode: LanguageServiceMode.PartialSemantic, useSingleInferredProject: true });
+            openFilesForSession([file], session);
+            const response = session.executeCommandSeq<protocol.QuickInfoRequest>({
+                command: protocol.CommandTypes.Quickinfo,
+                arguments: protocolFileLocationFromSubstring(file, "foo"),
+            }).response as protocol.QuickInfoResponseBody;
+
+            assert(stringContainsAt(response.displayString, "(approximation)", 0));
+        });
+
         it("open files are added to inferred project even if config file is present and semantic operations succeed", () => {
             const { host, session, file1, file2 } = setup();
             const service = session.getProjectService();