Provide TokenSyntax nodes for the import path in BuildConfiguration.canImport()

The compiler produces diagnostics for `canImport` checks, which requires
more source location information than was previously provided via
`BuildConfiguration.canImport`. Add in TokenSyntax nodes for each of
the elements in the import path so that the compiler has the syntax node
information it needs.

Author: DougGregor

Sources/SwiftIfConfig/BuildConfiguration.swift

@@ -9,6 +9,7 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
+import SwiftSyntax
 
 /// Describes the ordering of a sequence of bytes that make up a word of
 /// storage for a particular architecture.
@@ -114,15 +115,15 @@ public protocol BuildConfiguration {
   /// information, which will translate into the `version` argument.
   ///
   /// - Parameters:
-  ///   - importPath: A nonempty sequence of identifiers describing the
-  ///     imported module, which was written in source as a dotted sequence,
-  ///     e.g., `UIKit.UIViewController` will be passed in as the import path
-  ///     array `["UIKit", "UIViewController"]`.
+  ///   - importPath: A nonempty sequence of (token, identifier) pairs
+  ///     describing the imported module, which was written in source as a
+  ///     dotted sequence, e.g., `UIKit.UIViewController` will be passed in as
+  ///     the import path array `[(token, "UIKit"), (token, "UIViewController")]`.
   ///   - version: The version restriction on the imported module. For the
   ///     normal `canImport(<import-path>)` syntax, this will always be
   ///     `CanImportVersion.unversioned`.
   /// - Returns: Whether the module can be imported.
-  func canImport(importPath: [String], version: CanImportVersion) throws -> Bool
+  func canImport(importPath: [(TokenSyntax, String)], version: CanImportVersion) throws -> Bool
 
   /// Determine whether the given name is the active target OS (e.g., Linux, iOS).
   ///

Sources/SwiftIfConfig/IfConfigEvaluation.swift

@@ -443,7 +443,7 @@ func evaluateIfConfig(
       }
 
       // Extract the import path.
-      let importPath: [String]
+      let importPath: [(TokenSyntax, String)]
       do {
         importPath = try extractImportPath(firstArg.expression)
       } catch {
@@ -502,7 +502,7 @@ func evaluateIfConfig(
       return checkConfiguration(at: call) {
         (
           active: try configuration.canImport(
-            importPath: importPath.map { String($0) },
+            importPath: importPath,
             version: version
           ),
           syntaxErrorsAllowed: fn.syntaxErrorsAllowed
@@ -540,22 +540,22 @@ extension SyntaxProtocol {
 }
 
 /// Given an expression with the expected form A.B.C, extract the import path
-/// ["A", "B", "C"] from it. Throws an error if the expression doesn't match
-/// this form.
-private func extractImportPath(_ expression: some ExprSyntaxProtocol) throws -> [String] {
+/// ["A", "B", "C"] from it with the token syntax nodes for each name.
+/// Throws an error if the expression doesn't match this form.
+private func extractImportPath(_ expression: some ExprSyntaxProtocol) throws -> [(TokenSyntax, String)] {
   // Member access.
   if let memberAccess = expression.as(MemberAccessExprSyntax.self),
     let base = memberAccess.base,
     let memberName = memberAccess.declName.simpleIdentifier?.name
   {
-    return try extractImportPath(base) + [memberName]
+    return try extractImportPath(base) + [(memberAccess.declName.baseName, memberName)]
   }
 
   // Declaration reference.
   if let declRef = expression.as(DeclReferenceExprSyntax.self),
     let name = declRef.simpleIdentifier?.name
   {
-    return [name]
+    return [(declRef.baseName, name)]
   }
 
   throw IfConfigDiagnostic.expectedModuleName(syntax: ExprSyntax(expression))
@@ -794,7 +794,7 @@ private struct CanImportSuppressingBuildConfiguration<Other: BuildConfiguration>
     return try other.hasAttribute(name: name)
   }
 
-  func canImport(importPath: [String], version: CanImportVersion) throws -> Bool {
+  func canImport(importPath: [(TokenSyntax, String)], version: CanImportVersion) throws -> Bool {
     return false
   }