[NFC] Inject asSwiftSafeName as a dependency (apple#148)

[NFC] Inject asSwiftSafeName as a dependency

### Motivation

Arguably, we should have done this before, but here we go. In order to allow dynamically customizing the logic for converting OpenAPI to Swift identifiers (in support of staging SOAR-0001 gradually), we need to dependency-inject the `(String) -> String` function to all the places that need to do this conversion.

### Modifications

This PR doesn't change any behavior (NFC - no functional change), it just refactors the code to have a single funnel point through which all the conversion goes, which has access to the `Config` and can inspect feature flags.

Right now, the default behavior is still the same, but this PR creates room for adding the alternative logic from SOAR-0001.

### Result

NFC, prepares room for a subsequent PR.

Now it's possible to conditionalize the Swift name computing logic based on feature flags.

### Test Plan

All tests are passing, adapted as needed, created conveniences in tests for getting a default `Config`, but also made it possible to test the logic by explicitly passing the feature flag.


Reviewed by: simonjbeaumont

Builds:
     ✔︎ pull request validation (5.8) - Build finished. 
     ✔︎ pull request validation (5.9) - Build finished. 
     ✔︎ pull request validation (docc test) - Build finished. 
     ✔︎ pull request validation (integration test) - Build finished. 
     ✔︎ pull request validation (nightly) - Build finished. 
     ✔︎ pull request validation (soundness) - Build finished. 

apple#148

Author: czechboy0

Sources/_OpenAPIGeneratorCore/Extensions/String.swift

@@ -15,13 +15,6 @@ import Foundation
 
 extension String {
 
-    /// Returns a copy of the string modified to be a valid Swift identifier.
-    ///
-    /// For sanitization rules, see ``String/sanitizedForSwiftCode``.
-    var asSwiftSafeName: String {
-        sanitizedForSwiftCode
-    }
-
     /// Returns a copy of the string with the first letter uppercased.
     var uppercasingFirstLetter: String {
         transformingFirstLetter { $0.uppercased() }
@@ -33,12 +26,6 @@ extension String {
     }
 }
 
-fileprivate extension Character {
-
-    /// A Boolean value that indicates whether the character is an underscore.
-    var isUnderscore: Bool { self == "_" }
-}
-
 fileprivate extension String {
 
     /// Returns a copy of the string with the first letter modified by
@@ -53,171 +40,4 @@ fileprivate extension String {
             with: transformation(self[firstLetterIndex])
         )
     }
-
-    /// Returns a string sanitized to be usable as a Swift identifier.
-    ///
-    /// For example, the string `$nake` would be returned as `_nake`, because
-    /// the dollar sign is not a valid character in a Swift identifier.
-    ///
-    /// In addition to replacing illegal characters with an underscores, also
-    /// ensures that the identifier starts with a letter and not a number.
-    var sanitizedForSwiftCode: String {
-        guard !isEmpty else {
-            return "_empty"
-        }
-
-        // Only allow [a-zA-Z][a-zA-Z0-9_]*
-        // This is bad, is there something like percent encoding functionality but for general "allowed chars only"?
-
-        let firstCharSet: CharacterSet = .letters
-        let numbers: CharacterSet = .decimalDigits
-        let otherCharSet: CharacterSet = .alphanumerics.union(.init(charactersIn: "_"))
-
-        var sanitizedScalars: [Unicode.Scalar] = []
-        for (index, scalar) in unicodeScalars.enumerated() {
-            let allowedSet = index == 0 ? firstCharSet : otherCharSet
-            let outScalar: Unicode.Scalar
-            if allowedSet.contains(scalar) {
-                outScalar = scalar
-            } else if index == 0 && numbers.contains(scalar) {
-                sanitizedScalars.append("_")
-                outScalar = scalar
-            } else {
-                outScalar = "_"
-            }
-            sanitizedScalars.append(outScalar)
-        }
-
-        let validString = String(UnicodeScalarView(sanitizedScalars))
-
-        guard Self.keywords.contains(validString) else {
-            return validString
-        }
-        return "_\(validString)"
-    }
-
-    /// A list of Swift keywords.
-    ///
-    /// Copied from SwiftSyntax/TokenKind.swift
-    private static let keywords: Set<String> = [
-        "associatedtype",
-        "class",
-        "deinit",
-        "enum",
-        "extension",
-        "func",
-        "import",
-        "init",
-        "inout",
-        "let",
-        "operator",
-        "precedencegroup",
-        "protocol",
-        "struct",
-        "subscript",
-        "typealias",
-        "var",
-        "fileprivate",
-        "internal",
-        "private",
-        "public",
-        "static",
-        "defer",
-        "if",
-        "guard",
-        "do",
-        "repeat",
-        "else",
-        "for",
-        "in",
-        "while",
-        "return",
-        "break",
-        "continue",
-        "fallthrough",
-        "switch",
-        "case",
-        "default",
-        "where",
-        "catch",
-        "throw",
-        "as",
-        "Any",
-        "false",
-        "is",
-        "nil",
-        "rethrows",
-        "super",
-        "self",
-        "Self",
-        "true",
-        "try",
-        "throws",
-        "__FILE__",
-        "__LINE__",
-        "__COLUMN__",
-        "__FUNCTION__",
-        "__DSO_HANDLE__",
-        "_",
-        "(",
-        ")",
-        "{",
-        "}",
-        "[",
-        "]",
-        "<",
-        ">",
-        ".",
-        ".",
-        ",",
-        "...",
-        ":",
-        ";",
-        "=",
-        "@",
-        "#",
-        "&",
-        "->",
-        "`",
-        "\\",
-        "!",
-        "?",
-        "?",
-        "\"",
-        "\'",
-        "\"\"\"",
-        "#keyPath",
-        "#line",
-        "#selector",
-        "#file",
-        "#fileID",
-        "#filePath",
-        "#column",
-        "#function",
-        "#dsohandle",
-        "#assert",
-        "#sourceLocation",
-        "#warning",
-        "#error",
-        "#if",
-        "#else",
-        "#elseif",
-        "#endif",
-        "#available",
-        "#unavailable",
-        "#fileLiteral",
-        "#imageLiteral",
-        "#colorLiteral",
-        ")",
-        "yield",
-        "String",
-        "Error",
-        "Int",
-        "Bool",
-        "Array",
-        "Type",
-        "type",
-        "Protocol",
-        "await",
-    ]
 }

Sources/_OpenAPIGeneratorCore/FeatureFlags.swift

@@ -33,6 +33,12 @@ public enum FeatureFlag: String, Hashable, Equatable, Codable, CaseIterable {
     /// - https://github.com/apple/swift-openapi-generator/issues/6
     /// - https://github.com/apple/swift-openapi-generator/issues/7
     case multipleContentTypes
+
+    /// SOAR-0001 Improved OpenAPI -> Swift name mapping
+    ///
+    /// Tracking issues:
+    /// - https://github.com/apple/swift-openapi-generator/pull/95
+    case proposal0001
 }
 
 /// A set of enabled feature flags.

Sources/_OpenAPIGeneratorCore/Translator/ClientTranslator/ClientTranslator.swift

@@ -43,7 +43,11 @@ struct ClientFileTranslator: FileTranslator {
 
         let clientMethodDecls =
             try OperationDescription
-            .all(from: doc.paths, in: components)
+            .all(
+                from: doc.paths,
+                in: components,
+                asSwiftSafeName: swiftSafeName
+            )
             .map(translateClientMethod(_:))
 
         let clientStructPropertyDecl: Declaration = .commentable(