Templating: Optionally save interpolated expressions when replacing variables in a string (#65411)

* Testing a refactor

* update

* Update interface, test interoplations map

* Refactoring

* Add more explicit comment about new behavior

* Update packages/grafana-runtime/src/services/templateSrv.ts

Co-authored-by: Torkel Ödegaard <torkel@grafana.com>

---------

Co-authored-by: Torkel Ödegaard <torkel@grafana.com>

packages/grafana-runtime/src/services/templateSrv.ts

@@ -1,5 +1,23 @@
 import { ScopedVars, TimeRange, TypedVariableModel } from '@grafana/data';
 
+/**
+ * Can be used to gain more information about an interpolation operation
+ */
+export interface VariableInterpolation {
+  /** The full matched expression including, example: ${varName.field:regex} */
+  match: string;
+  /** In the expression ${varName.field:regex} variableName is varName */
+  variableName: string;
+  /** In the expression ${varName.fields[0].name:regex} the fieldPath is fields[0].name */
+  fieldPath?: string;
+  /** In the expression ${varName:regex} the regex part is the format */
+  format?: string;
+  /** The formatted value of the variable expresion. Will equal match when variable not found or scopedVar was undefined or null **/
+  value: string;
+  // When value === match this will be true, meaning the variable was not found
+  found?: boolean;
+}
+
 /**
  * Via the TemplateSrv consumers get access to all the available template variables
  * that can be used within the current active dashboard.
@@ -15,8 +33,19 @@ export interface TemplateSrv {
 
   /**
    * Replace the values within the target string.  See also {@link InterpolateFunction}
+   *
+   * Note: interpolations array is being mutated by replace function by adding information about variables that
+   * have been interpolated during replacement. Variables that were specified in the target but not found in
+   * the list of available variables are also added to the array. See {@link VariableInterpolation} for more details.
+   *
+   * @param {VariableInterpolation[]} interpolations an optional map that is updated with interpolated variables
    */
-  replace(target?: string, scopedVars?: ScopedVars, format?: string | Function): string;
+  replace(
+    target?: string,
+    scopedVars?: ScopedVars,
+    format?: string | Function,
+    interpolations?: VariableInterpolation[]
+  ): string;
 
   /**
    * Checks if a target contains template variables.