fix prefix generation and test cases

src/compiler/compile/index.ts

@@ -26,7 +26,8 @@ const valid_options = [
 	'css',
 	'loopGuardTimeout',
 	'preserveComments',
-	'preserveWhitespace'
+	'preserveWhitespace',
+	'prefix',
 ];
 
 function validate_options(options: CompileOptions, warnings: Warning[]) {

src/compiler/compile/utils/get_prefix.ts

@@ -2,7 +2,7 @@ export default function get_prefix(str?: string): string {
     const standard_prefix = 'svelte-';
     if (!str
         || typeof str !== 'string') return standard_prefix;
-    str = str.replace(/^[^_-a-z]+|[^_-a-z0-9]/gi, '');
+    str = str.replace(/^[^_\-a-z]+|[^_\-a-z0-9]/gi, '');
     return str.length
         ? str
         : standard_prefix;

test/css/samples/custom-prefix-has-only-disallowed-characters/expected.css

@@ -1 +1 @@
-div.svelte-xyz{color:blue}
+div.svelte-1tjtw78{color:blue}

test/css/samples/custom-prefix-has-special-character/expected.css

@@ -1 +1 @@
-div.me-xyz{color:blue}
+div.me-1tjtw78{color:blue}

test/css/samples/custom-prefix-has-whitespace/expected.css

@@ -1 +1 @@
-div.me-xyz{color:blue}
+div.me-1tjtw78{color:blue}

test/css/samples/custom-prefix-no-string/expected.css

@@ -1 +1 @@
-div.svelte-xyz{color:blue}
+div.svelte-1tjtw78{color:blue}

test/css/samples/custom-prefix-starts-with-number/expected.css

@@ -1 +1 @@
-div.me-xyz{color:blue}
+div.me-1tjtw78{color:blue}

test/css/samples/custom-prefix-starts-with-whitespace/expected.css

@@ -1 +1 @@
-div.me-xyz{color:blue}
+div.me-1tjtw78{color:blue}

test/css/samples/custom-prefix/expected.css

@@ -1 +1 @@
-div.me-xyz{color:blue}
+div.me-1tjtw78{color:blue}