🚸 Improve error message for wrong database/user

CHANGELOG.md

@@ -2,13 +2,33 @@
 
 ## Unreleased
 
-- Use `postgres` as the default user in case the `PGUSER` env variable is not
-  set.
-- Add support for `varchar` and `bpchar` types.
+- Squirrel now uses `"postgres"` as the default user in case the `PGUSER`
+  environment variable is not set.
+  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))
+
+- Added support for the `varchar` and `bpchar` types, mapped to Gleam `String`s.
+  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))
+
+- Improved the error message in case Squirrel cannot connect to the Postgres
+  server with the given database and username.
+  Instead of a not-really-helpful `Cannot receive message: Closed` the error now
+  properly explains what went wrong and hot to solve the issue:
+
+  ```
+  Error: Cannot connect
+
+  I couldn't connect to database `database` with user `postgres`.
+
+  Hint: You can change the default user and database by setting the `PGUSER` and
+  `PGDATABASE` environment variables.
+  ```
+
+  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))
 
 ## v1.0.1 - 2024-08-09
 
-- Fix a bug with the code generation of `Option` types.
+- Fixed a bug with the code generation of `Option` types.
+  ([Giacomo Cavalieri](https://github.com/giacomocavalieri))
 
 ## v1.0.0 - 2024-08-09
 

src/squirrel/internal/database/postgres.gleam

@@ -28,9 +28,9 @@ import gleam/string
 import squirrel/internal/database/postgres_protocol as pg
 import squirrel/internal/error.{
   type Error, type Pointer, type ValueIdentifierError, ByteIndex,
-  CannotParseQuery, PgCannotAuthenticate, PgCannotDecodeReceivedMessage,
-  PgCannotDescribeQuery, PgCannotReceiveMessage, PgCannotSendMessage, Pointer,
-  QueryHasInvalidColumn, QueryHasUnsupportedType,
+  CannotParseQuery, PgCannotAuthenticate, PgCannotConnectUserDatabase,
+  PgCannotDecodeReceivedMessage, PgCannotDescribeQuery, PgCannotReceiveMessage,
+  PgCannotSendMessage, Pointer, QueryHasInvalidColumn, QueryHasUnsupportedType,
 }
 import squirrel/internal/eval_extra
 import squirrel/internal/gleam
@@ -254,7 +254,17 @@ fn authenticate(connection: ConnectionOptions) -> Db(Nil) {
     _ -> unexpected_message(PgCannotAuthenticate, "AuthenticationOk", msg)
   })
 
-  use _ <- eval.try(wait_until_ready())
+  use _ <- eval.try(
+    wait_until_ready()
+    // In case there's a receive error while waiting for the server to be ready
+    // we want to display a more helpful error message because the problem here
+    // must be with an invalid username/database combination.
+    |> eval.replace_error(PgCannotConnectUserDatabase(
+      user: connection.user,
+      database: connection.database,
+    )),
+  )
+
   eval.return(Nil)
 }
 

src/squirrel/internal/error.gleam

@@ -10,9 +10,12 @@ import simplifile
 
 pub type Error {
   // --- POSTGRES RELATED ERRORS -----------------------------------------------
+  /// When the server immediately closes the connection right after we try to
+  /// connect using the given username and database.
+  ///
+  PgCannotConnectUserDatabase(user: String, database: String)
+
   /// When authentication workflow goes wrong.
-  /// TODO)) For now I only support no authentication so people might report
-  /// this issue.
   ///
   PgCannotAuthenticate(expected: String, got: String)
 
@@ -127,6 +130,31 @@ pub fn to_doc(error: Error) -> Document {
   // that is actually printed and we do not have to make any effort to add and
   // print new errors.
   let printable_error = case error {
+    PgCannotConnectUserDatabase(user: user, database: database) ->
+      printable_error("Cannot connect")
+      |> add_paragraph(
+        "I couldn't connect to database "
+        <> style_inline_code(database)
+        <> " with user "
+        <> style_inline_code(user)
+        <> ".",
+      )
+      |> hint(
+        "You can change the default user and database by setting the "
+        <> style_inline_code("PGUSER")
+        <> " and "
+        <> style_inline_code("PGDATABASE")
+        <> " environment variables.",
+      )
+
+    PgCannotAuthenticate(expected: expected, got: got) ->
+      printable_error("Cannot authenticate")
+      |> add_paragraph(
+        "I ran into an unexpected problem while trying to authenticate with the
+Postgres server. This is most definitely a bug!",
+      )
+      |> report_bug("Expected: " <> expected <> ", Got: " <> got)
+
     PgCannotSendMessage(reason: reason) ->
       printable_error("Cannot send message")
       |> add_paragraph(
@@ -151,6 +179,18 @@ database server.",
       )
       |> report_bug(reason)
 
+    PgCannotDescribeQuery(
+      file: file,
+      query_name: query_name,
+      expected: expected,
+      got: got,
+    ) ->
+      printable_error("Cannot inspect query")
+      |> add_paragraph("I ran into an unexpected problem while trying to figure
+out the types of query " <> style_inline_code(query_name) <> "
+defined in " <> style_file(file) <> ". This is most definitely a bug!")
+      |> report_bug("Expected: " <> expected <> ", Got: " <> got)
+
     CannotReadFile(file: file, reason: reason) ->
       printable_error("Cannot read file")
       |> add_paragraph(
@@ -274,26 +314,6 @@ contain lowercase letters, numbers and underscores.",
         starting_line: starting_line,
       )
       |> maybe_hint(hint)
-
-    PgCannotAuthenticate(expected: expected, got: got) ->
-      printable_error("Cannot authenticate")
-      |> add_paragraph(
-        "I ran into an unexpected problem while trying to authenticate with the
-Postgres server. This is most definitely a bug!",
-      )
-      |> report_bug("Expected: " <> expected <> ", Got: " <> got)
-
-    PgCannotDescribeQuery(
-      file: file,
-      query_name: query_name,
-      expected: expected,
-      got: got,
-    ) ->
-      printable_error("Cannot inspect query")
-      |> add_paragraph("I ran into an unexpected problem while trying to figure
-out the types of query " <> style_inline_code(query_name) <> "
-defined in " <> style_file(file) <> ". This is most definitely a bug!")
-      |> report_bug("Expected: " <> expected <> ", Got: " <> got)
   }
 
   printable_error_to_doc(printable_error)