[compiler] Move capitalize to compiler

.chronus/changes/capitalize-util-2025-4-1-15-35-12.md

@@ -0,0 +1,9 @@
+---
+changeKind: feature
+packages:
+  - "@typespec/compiler"
+  - "@typespec/openapi3"
+  - "@typespec/protobuf"
+---
+
+Add "capitalize" string helper to compiler

packages/compiler/package.json

@@ -59,6 +59,9 @@
     },
     "./internals/prettier-formatter": {
       "import": "./dist/src/internals/prettier-formatter.js"
+    },
+    "./casing": {
+      "import": "./dist/src/casing/index.js"
     }
   },
   "browser": {

packages/compiler/src/casing/index.ts

@@ -0,0 +1,6 @@
+/**
+ * Simple utility function to capitalize a string.
+ */
+export function capitalize<S extends string>(s: S): Capitalize<S> {
+  return (s.charAt(0).toUpperCase() + s.slice(1)) as Capitalize<S>;
+}

packages/compiler/src/typekit/utils/get-plausible-name.ts

@@ -1,3 +1,4 @@
+import { capitalize } from "../../casing/index.js";
 import { isTemplateInstance } from "../../core/type-utils.js";
 import { Enum, Interface, Model, Scalar, Union } from "../../core/types.js";
 
@@ -14,9 +15,9 @@ export function getPlausibleName(type: Model | Union | Enum | Scalar | Interface
         if (a.entityKind === "Type") {
           switch (a.kind) {
             case "Scalar":
-              // Box<scalar> is not a scalar so capital case naming convention applies
               const name = getPlausibleName(a);
-              return name.charAt(0).toUpperCase() + name.slice(1);
+              // Box<scalar> is not a scalar so capital case naming convention applies
+              return capitalize(name);
             case "Model":
             case "Interface":
             case "Enum":

packages/compiler/test/casing.test.ts

@@ -0,0 +1,16 @@
+import { describe, expect, it } from "vitest";
+import { capitalize } from "../src/casing/index.js";
+
+describe("capitalize", () => {
+  it("should capitalize the first letter of a string", () => {
+    expect(capitalize("hello world")).toEqual("Hello world");
+  });
+
+  it("should return an empty string when input is empty", () => {
+    expect(capitalize("")).toEqual("");
+  });
+
+  it("should handle single-character strings", () => {
+    expect(capitalize("a")).toEqual("A");
+  });
+});

packages/openapi3/src/schema-emitter.ts

@@ -53,6 +53,7 @@ import {
   isSecret,
   resolveEncodedName,
 } from "@typespec/compiler";
+import { capitalize } from "@typespec/compiler/casing";
 import { $ } from "@typespec/compiler/typekit";
 import { MetadataInfo, Visibility, getVisibilitySuffix } from "@typespec/http";
 import {
@@ -860,10 +861,3 @@ export const Builders = {
     return builder;
   },
 } as const;
-
-/**
- * Simple utility function to capitalize a string.
- */
-function capitalize<S extends string>(s: S) {
-  return (s.slice(0, 1).toUpperCase() + s.slice(1)) as Capitalize<S>;
-}

packages/protobuf/src/transform/index.ts

@@ -27,6 +27,7 @@ import {
   Union,
 } from "@typespec/compiler";
 import { SyntaxKind } from "@typespec/compiler/ast";
+import { capitalize } from "@typespec/compiler/casing";
 import {
   map,
   matchType,
@@ -1005,13 +1006,6 @@ function isArray(t: Type) {
   return t.kind === "Model" && t.name === "Array" && t.namespace?.name === "TypeSpec";
 }
 
-/**
- * Simple utility function to capitalize a string.
- */
-function capitalize<S extends string>(s: S) {
-  return (s.slice(0, 1).toUpperCase() + s.slice(1)) as Capitalize<S>;
-}
-
 /**
  * Gets the syntactic return type target for an operation.
  *