Add a macro helper to get string literal value

Sources/ScreamURITemplateCompilerPlugin/ExprSyntax+Literals.swift

@@ -0,0 +1,27 @@
+//   Copyright 2018-2024 Alex Deem
+//
+//   Licensed under the Apache License, Version 2.0 (the "License");
+//   you may not use this file except in compliance with the License.
+//   You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+//   Unless required by applicable law or agreed to in writing, software
+//   distributed under the License is distributed on an "AS IS" BASIS,
+//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//   See the License for the specific language governing permissions and
+//   limitations under the License.
+
+import SwiftSyntax
+
+extension ExprSyntax {
+    func stringLiteral() -> String? {
+        guard let segments = self.as(StringLiteralExprSyntax.self)?.segments,
+              segments.count == 1,
+              case let .stringSegment(literalSegment)? = segments.first else {
+            return nil
+        }
+
+        return literalSegment.content.text
+    }
+}

Sources/ScreamURITemplateCompilerPlugin/URITemplateMacro.swift

@@ -24,22 +24,19 @@ public struct URITemplateMacro: ExpressionMacro {
         of node: some FreestandingMacroExpansionSyntax,
         in _: some MacroExpansionContext) throws -> ExprSyntax {
         guard let argument = node.arguments.first?.expression,
-              let segments = argument.as(StringLiteralExprSyntax.self)?.segments,
-              segments.count == 1,
-              case let .stringSegment(literalSegment)? = segments.first
+              let uriTemplateString = argument.stringLiteral()
         else {
             throw DiagnosticsError(diagnostics: [
                 Diagnostic(node: node,
                            message: MacroExpansionErrorMessage("#URITemplate requires a static string literal")),
             ])
         }
 
-        let uriTemplateString = literalSegment.content.text
         do {
             _ = try URITemplate(string: uriTemplateString)
         } catch {
             throw DiagnosticsError(diagnostics: [
-                Diagnostic(node: literalSegment,
+                Diagnostic(node: argument,
                            message: MacroExpansionErrorMessage("Invalid URI template: \(error.reason) at \"\(uriTemplateString.suffix(from: error.position).prefix(50))\"")),
             ])
         }

Tests/ScreamURITemplateTests/MacroTests.swift

@@ -48,7 +48,7 @@
                 #URITemplate("https://api.github.com/repos/{}/{repo}")
                 """#,
                 diagnostics: [
-                    DiagnosticSpec(message: "Invalid URI template: Empty Variable Name at \"}/{repo}\"", line: 1, column: 15),
+                    DiagnosticSpec(message: "Invalid URI template: Empty Variable Name at \"}/{repo}\"", line: 1, column: 14),
                 ],
                 macros: testMacros)
         }