Don’t treat keywords used as function names as keywords

Swift enables the use of keywords as function names, and we want those
to be treated as plain text (like other function names) rather than as
keywords. Some keywords require escaping using back-ticks, and this
patch accounts for both of those variations.

Sources/Splash/Grammar/SwiftGrammar.swift

@@ -221,6 +221,10 @@ private extension SwiftGrammar {
                         return false
                     }
                 }
+
+                guard !segment.tokens.previous.isAny(of: "func", "`") else {
+                    return false
+                }
             }
 
             return keywords.contains(segment.tokens.current)

Tests/SplashTests/Tests/DeclarationTests.swift

@@ -520,6 +520,50 @@ final class DeclarationTests: SyntaxHighlighterTestCase {
         ])
     }
 
+    func testFunctionDeclarationWithNonEscapedKeywordAsName() {
+        let components = highlighter.highlight("func get() -> Int { return 7 }")
+
+        XCTAssertEqual(components, [
+            .token("func", .keyword),
+            .whitespace(" "),
+            .plainText("get()"),
+            .whitespace(" "),
+            .plainText("->"),
+            .whitespace(" "),
+            .token("Int", .type),
+            .whitespace(" "),
+            .plainText("{"),
+            .whitespace(" "),
+            .token("return", .keyword),
+            .whitespace(" "),
+            .token("7", .number),
+            .whitespace(" "),
+            .plainText("}")
+        ])
+    }
+
+    func testFunctionDeclarationWithEscapedKeywordAsName() {
+        let components = highlighter.highlight("func `public`() -> Int { return 7 }")
+
+        XCTAssertEqual(components, [
+            .token("func", .keyword),
+            .whitespace(" "),
+            .plainText("`public`()"),
+            .whitespace(" "),
+            .plainText("->"),
+            .whitespace(" "),
+            .token("Int", .type),
+            .whitespace(" "),
+            .plainText("{"),
+            .whitespace(" "),
+            .token("return", .keyword),
+            .whitespace(" "),
+            .token("7", .number),
+            .whitespace(" "),
+            .plainText("}")
+        ])
+    }
+
     func testIndirectEnumDeclaration() {
         let components = highlighter.highlight("""
         indirect enum Content {
@@ -583,6 +627,8 @@ extension DeclarationTests {
             ("testSubscriptDeclaration", testSubscriptDeclaration),
             ("testDeferDeclaration", testDeferDeclaration),
             ("testFunctionDeclarationWithInOutParameter", testFunctionDeclarationWithInOutParameter),
+            ("testFunctionDeclarationWithNonEscapedKeywordAsName", testFunctionDeclarationWithNonEscapedKeywordAsName),
+            ("testFunctionDeclarationWithEscapedKeywordAsName", testFunctionDeclarationWithEscapedKeywordAsName),
             ("testIndirectEnumDeclaration", testIndirectEnumDeclaration)
         ]
     }