feat: add list instance emails endpoint and use Select in AddUser

Add a new GET /users/list_instance_emails endpoint that returns all
instance user emails (from the password table). This endpoint is only
available on non-cloud instances.

In the frontend AddUser component, when the instance emails are
available (non-cloud), replace the email text input with a Select
component that allows both selecting from existing instance users and
typing custom emails.

Closes #7902

Co-authored-by: windmill-internal-app[bot] <windmill-internal-app[bot]@users.noreply.github.com>

backend/.sqlx/query-21e9a9fc33dcdb66a2c8e95b1359ca1b3e04b4ecf155757abf5798834ebfd0ce.json

@@ -0,0 +1,20 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "SELECT email FROM password ORDER BY email",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "email",
+        "type_info": "Varchar"
+      }
+    ],
+    "parameters": {
+      "Left": []
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "21e9a9fc33dcdb66a2c8e95b1359ca1b3e04b4ecf155757abf5798834ebfd0ce"
+}

backend/windmill-api-users/src/users.rs

@@ -86,6 +86,10 @@ pub fn global_service() -> Router {
         .route("/decline_invite", post(decline_invite))
         .route("/accept_invite", post(accept_invite))
         .route("/list_as_super_admin", get(list_users_as_super_admin))
+        .route(
+            "/list_instance_emails",
+            get(list_instance_emails),
+        )
         .route("/set_login_type/:user", post(set_login_type))
         .route("/update/:user", post(update_user))
         .route("/delete/:user", delete(delete_user))
@@ -420,6 +424,21 @@ async fn list_users_as_super_admin(
     Ok(Json(rows))
 }
 
+async fn list_instance_emails(
+    _authed: ApiAuthed,
+    Extension(db): Extension<DB>,
+) -> JsonResult<Vec<String>> {
+    if *CLOUD_HOSTED {
+        return Err(Error::BadRequest(
+            "This endpoint is not available on cloud hosted instances".to_string(),
+        ));
+    }
+    let rows = sqlx::query_scalar!("SELECT email FROM password ORDER BY email")
+        .fetch_all(&db)
+        .await?;
+    Ok(Json(rows))
+}
+
 #[derive(Serialize, Deserialize)]
 struct Progress {
     progress: u64,

backend/windmill-api/openapi.yaml

@@ -2306,6 +2306,22 @@ paths:
                 items:
                   $ref: "#/components/schemas/GlobalUserInfo"
 
+  /users/list_instance_emails:
+    get:
+      summary: list all instance user emails (only on non-cloud instances)
+      operationId: listInstanceEmails
+      tags:
+        - user
+      responses:
+        "200":
+          description: list of instance user emails
+          content:
+            application/json:
+              schema:
+                type: array
+                items:
+                  type: string
+
   /w/{workspace}/workspaces/list_pending_invites:
     get:
       summary: list pending invites for a workspace

frontend/src/lib/components/AddUser.svelte

@@ -10,6 +10,7 @@
 	import ToggleButtonGroup from './common/toggleButton-v2/ToggleButtonGroup.svelte'
 	import ToggleButton from './common/toggleButton-v2/ToggleButton.svelte'
 	import { UserPlus } from 'lucide-svelte'
+	import Select from './select/Select.svelte'
 
 	const dispatch = createEventDispatcher()
 
@@ -31,6 +32,19 @@
 	}
 	getAutomateUsernameCreationSetting()
 
+	let instanceEmails: { label: string; value: string }[] | undefined = $state(undefined)
+
+	async function loadInstanceEmails() {
+		if (isCloudHosted()) return
+		try {
+			const emails = await UserService.listInstanceEmails()
+			instanceEmails = emails.map((e) => ({ label: e, value: e }))
+		} catch {
+			instanceEmails = undefined
+		}
+	}
+	loadInstanceEmails()
+
 	async function addUser() {
 		await WorkspaceService.addUser({
 			workspace: $workspaceStore!,
@@ -84,7 +98,25 @@
 			<span class="text-sm mb-2 leading-6 font-semibold">Add a new user</span>
 
 			<span class="text-xs mb-1 leading-6">Email</span>
-			<input type="email mb-1" onkeyup={handleKeyUp} placeholder="email" bind:value={email} />
+			{#if instanceEmails}
+				<Select
+					items={instanceEmails}
+					bind:value={email}
+					placeholder="Select or type an email"
+					createText="Use custom email:"
+					onCreateItem={(v) => {
+						email = v
+					}}
+					disablePortal={true}
+				/>
+			{:else}
+				<input
+					type="email"
+					onkeyup={handleKeyUp}
+					placeholder="email"
+					bind:value={email}
+				/>
+			{/if}
 
 			{#if !automateUsernameCreation}
 				<span class="text-xs mb-1 pt-2 leading-6">Username</span>