Add macro to perform compile-time template processing

Sources/ScreamURITemplateCompilerPlugin/ExprSyntax+Literals.swift

@@ -24,4 +24,21 @@ extension ExprSyntax {
 
         return literalSegment.content.text
     }
+
+    func dictionaryLiteral() -> [String: String]? {
+        guard let elements = self.as(DictionaryExprSyntax.self)?.content.as(DictionaryElementListSyntax.self) else {
+            return nil
+        }
+
+        var result: [String: String] = [:]
+        for element in elements {
+            guard let key = element.key.stringLiteral(),
+                  let value = element.value.stringLiteral() else {
+                return nil
+            }
+            result[key] = value
+        }
+
+        return result
+    }
 }

Sources/ScreamURITemplateCompilerPlugin/URITemplateCompilerPlugin.swift

@@ -17,5 +17,8 @@ import SwiftSyntaxMacros
 
 @main
 struct URITemplateCompilerPlugin: CompilerPlugin {
-    var providingMacros: [Macro.Type] = [URITemplateMacro.self]
+    var providingMacros: [Macro.Type] = [
+        URITemplateMacro.self,
+        URLByExpandingURITemplateMacro.self,
+    ]
 }

Sources/ScreamURITemplateCompilerPlugin/URLByExpandingURITemplateMacro.swift

@@ -0,0 +1,72 @@
+//   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 Foundation
+import SwiftCompilerPlugin
+import SwiftDiagnostics
+import SwiftSyntax
+import SwiftSyntaxMacros
+
+import ScreamURITemplate
+
+public struct URLByExpandingURITemplateMacro: ExpressionMacro {
+    public static func expansion(
+        of node: some FreestandingMacroExpansionSyntax,
+        in _: some MacroExpansionContext) throws -> ExprSyntax {
+        guard let templateArgument = node.arguments.first?.expression,
+              let uriTemplateString = templateArgument.stringLiteral() else {
+            throw DiagnosticsError(diagnostics: [
+                Diagnostic(node: node,
+                           message: MacroExpansionErrorMessage("#URLByExpandingURITemplate requires a static string literal for the first argument")),
+            ])
+        }
+
+        guard let paramsArgument = node.arguments.last?.expression,
+              let params = paramsArgument.dictionaryLiteral() else {
+            throw DiagnosticsError(diagnostics: [
+                Diagnostic(node: node,
+                           message: MacroExpansionErrorMessage("#URLByExpandingURITemplate requires a Dictionary Literal of string literals for the second argument")),
+            ])
+        }
+
+        let template: URITemplate
+        do {
+            template = try URITemplate(string: uriTemplateString)
+        } catch {
+            throw DiagnosticsError(diagnostics: [
+                Diagnostic(node: templateArgument,
+                           message: MacroExpansionErrorMessage("Invalid URI template: \(error.reason) at \"\(uriTemplateString.suffix(from: error.position).prefix(50))\"")),
+            ])
+        }
+
+        let processedTemplate: String
+        do {
+            processedTemplate = try template.process(variables: params)
+        } catch {
+            throw DiagnosticsError(diagnostics: [
+                Diagnostic(node: node,
+                           message: MacroExpansionErrorMessage("Failed to process template: \(error.reason)")),
+            ])
+        }
+
+        guard URL(string: processedTemplate) != nil else {
+            throw DiagnosticsError(diagnostics: [
+                Diagnostic(node: node,
+                           message: MacroExpansionErrorMessage("Processed template does not form a valid URL\n\(processedTemplate)")),
+            ])
+        }
+
+        return "URL(string: \(processedTemplate.makeLiteralSyntax()))!"
+    }
+}

Sources/ScreamURITemplateExample/main.swift

@@ -31,3 +31,7 @@ print(url.absoluteString)
 
 let macroExpansion = #URITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}")
 print(macroExpansion)
+
+let urlExpansion = #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}",
+                                              with: ["owner": "SwiftScream", "repo": "URITemplate", "username": "alexdeem"])
+print(urlExpansion)

Sources/ScreamURITemplateMacros/Macros.swift

@@ -12,6 +12,7 @@
 //   See the License for the specific language governing permissions and
 //   limitations under the License.
 
+import Foundation
 import ScreamURITemplate
 
 /// Macro providing compile-time validation of a URITemplate represented by a string literal
@@ -24,3 +25,15 @@ import ScreamURITemplate
 /// - Returns: A `URITemplate` constructed from the string literal
 @freestanding(expression)
 public macro URITemplate(_ stringLiteral: StaticString) -> URITemplate = #externalMacro(module: "ScreamURITemplateCompilerPlugin", type: "URITemplateMacro")
+
+/// Macro providing compile-time validation and processing of a URITemplate and parameters entirely represented by string literals
+/// Example:
+/// ```swift
+/// let template = #URLByExpandingURITemplate("https://api.github.com/repos/{owner}", with: ["owner": "SwiftScream"])
+/// ```
+/// - Parameters:
+///   - : A string literal representing the URI Template
+///   - with: The parameters to use to process the template, represented by a dictionary literal where the keys and values are all string literals
+/// - Returns: A `URL` constructed from the result of processing the template with the parameters
+@freestanding(expression)
+public macro URLByExpandingURITemplate(_ stringLiteral: StaticString, with: KeyValuePairs<StaticString, StaticString>) -> URL = #externalMacro(module: "ScreamURITemplateCompilerPlugin", type: "URLByExpandingURITemplateMacro")

Tests/ScreamURITemplateTests/URLByExpandingURITemplateMacroTests.swift

@@ -0,0 +1,167 @@
+//   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.
+
+#if canImport(ScreamURITemplateCompilerPlugin)
+    import ScreamURITemplateCompilerPlugin
+
+    import SwiftSyntaxMacros
+    import SwiftSyntaxMacrosTestSupport
+
+    import XCTest
+
+    class URLByExpandingURITemplateMacroTests: XCTestCase {
+        let testMacros: [String: Macro.Type] = [
+            "URLByExpandingURITemplate": URLByExpandingURITemplateMacro.self,
+        ]
+
+        func testValid() throws {
+            assertMacroExpansion(
+                #"""
+                #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}", [
+                    "owner": "SwiftScream",
+                    "repo": "URITemplate",
+                    "username": "alexdeem",
+                ])
+                """#,
+                expandedSource:
+                #"""
+                URL(string: "https://api.github.com/repos/SwiftScream/URITemplate/collaborators/alexdeem")!
+                """#,
+                diagnostics: [],
+                macros: testMacros)
+        }
+
+        func testInvalidTemplate() throws {
+            assertMacroExpansion(
+                #"""
+                #URLByExpandingURITemplate("https://api.github.com/repos/{}/{repo}/collaborators/{username}", [
+                    "owner": "SwiftScream",
+                    "repo": "URITemplate",
+                    "username": "alexdeem",
+                ])
+                """#,
+                expandedSource:
+                #"""
+                #URLByExpandingURITemplate("https://api.github.com/repos/{}/{repo}/collaborators/{username}", [
+                    "owner": "SwiftScream",
+                    "repo": "URITemplate",
+                    "username": "alexdeem",
+                ])
+                """#,
+                diagnostics: [
+                    DiagnosticSpec(message: "Invalid URI template: Empty Variable Name at \"}/{repo}/collaborators/{username}\"", line: 1, column: 28),
+                ],
+                macros: testMacros)
+        }
+
+        func testInvalidURL() throws {
+            assertMacroExpansion(
+                #"""
+                #URLByExpandingURITemplate("{nope}", ["nope": ""])
+                """#,
+                expandedSource:
+                #"""
+                #URLByExpandingURITemplate("{nope}", ["nope": ""])
+                """#,
+                diagnostics: [
+                    DiagnosticSpec(message: "Processed template does not form a valid URL\n", line: 1, column: 1),
+                ],
+                macros: testMacros)
+        }
+
+        func testMisusedTemplate() throws {
+            assertMacroExpansion(
+                #"""
+                let s: StaticString = "https://api.github.com/repos/{owner}"
+                #URLByExpandingURITemplate(s, [
+                    "owner": "SwiftScream",
+                ])
+                """#,
+                expandedSource:
+                #"""
+                let s: StaticString = "https://api.github.com/repos/{owner}"
+                #URLByExpandingURITemplate(s, [
+                    "owner": "SwiftScream",
+                ])
+                """#,
+                diagnostics: [
+                    DiagnosticSpec(message: "#URLByExpandingURITemplate requires a static string literal for the first argument", line: 2, column: 1),
+                ],
+                macros: testMacros)
+        }
+
+        func testMisusedParams() throws {
+            assertMacroExpansion(
+                #"""
+                let params: KeyValue<StaticString, StaticString> = ["owner": "SwiftScream"]
+                #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}", params)
+                """#,
+                expandedSource:
+                #"""
+                let params: KeyValue<StaticString, StaticString> = ["owner": "SwiftScream"]
+                #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}", params)
+                """#,
+                diagnostics: [
+                    DiagnosticSpec(message: "#URLByExpandingURITemplate requires a Dictionary Literal of string literals for the second argument", line: 2, column: 1),
+                ],
+                macros: testMacros)
+        }
+
+        func testMisusedParamKey() throws {
+            assertMacroExpansion(
+                #"""
+                #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}", [
+                    "owner": "SwiftScream",
+                    123: "URITemplate",
+                    "username": "alexdeem",
+                ])
+                """#,
+                expandedSource:
+                #"""
+                #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}", [
+                    "owner": "SwiftScream",
+                    123: "URITemplate",
+                    "username": "alexdeem",
+                ])
+                """#,
+                diagnostics: [
+                    DiagnosticSpec(message: "#URLByExpandingURITemplate requires a Dictionary Literal of string literals for the second argument", line: 1, column: 1),
+                ],
+                macros: testMacros)
+        }
+
+        func testMisusedParamValue() throws {
+            assertMacroExpansion(
+                #"""
+                #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}", [
+                    "owner": "SwiftScream",
+                    "repo": 12345,
+                    "username": "alexdeem",
+                ])
+                """#,
+                expandedSource:
+                #"""
+                #URLByExpandingURITemplate("https://api.github.com/repos/{owner}/{repo}/collaborators/{username}", [
+                    "owner": "SwiftScream",
+                    "repo": 12345,
+                    "username": "alexdeem",
+                ])
+                """#,
+                diagnostics: [
+                    DiagnosticSpec(message: "#URLByExpandingURITemplate requires a Dictionary Literal of string literals for the second argument", line: 1, column: 1),
+                ],
+                macros: testMacros)
+        }
+    }
+#endif