Prometheus: Fix label value suggestion (#21294)

* Prometheus: Fix label value suggestion

- remove quotes from typeahead input to suggest correct label values
- fix acceptance of partial label values

* Disable mid-word suggestions

* Fix test

public/app/plugins/datasource/prometheus/language_provider.ts

@@ -88,7 +88,10 @@ export default class PromQlLanguageProvider extends LanguageProvider {
   cleanText(s: string) {
     const parts = s.split(PREFIX_DELIMITER_REGEX);
     const last = parts.pop();
-    return last.trimLeft().replace(/"$/, '');
+    return last
+      .trimLeft()
+      .replace(/"$/, '')
+      .replace(/^"/, '');
   }
 
   get syntax() {
@@ -297,8 +300,15 @@ export default class PromQlLanguageProvider extends LanguageProvider {
     labelKey,
     value,
   }: TypeaheadInput): Promise<TypeaheadOutput> => {
+    const suggestions: CompletionItemGroup[] = [];
     const line = value.anchorBlock.getText();
     const cursorOffset = value.selection.anchor.offset;
+    const nextChar = line[cursorOffset];
+    const isValueContext = wrapperClasses.includes('attr-value');
+    if (!nextChar.match(/["}]/)) {
+      // Don't suggest anything inside a value
+      return { suggestions };
+    }
 
     // Get normalized selector
     let selector;
@@ -313,7 +323,6 @@ export default class PromQlLanguageProvider extends LanguageProvider {
     const containsMetric = selector.includes('__name__=');
     const existingKeys = parsedSelector ? parsedSelector.labelKeys : [];
 
-    const suggestions: CompletionItemGroup[] = [];
     let labelValues;
     // Query labels for selector
     if (selector) {
@@ -326,7 +335,7 @@ export default class PromQlLanguageProvider extends LanguageProvider {
     }
 
     let context: string;
-    if ((text && text.match(/^!?=~?/)) || wrapperClasses.includes('attr-value')) {
+    if ((text && text.match(/^!?=~?/)) || isValueContext) {
       // Label values
       if (labelKey && labelValues[labelKey]) {
         context = 'context-label-values';