Merge #238

238: Improve error messages when serde_as is used wrongly or misleadingly r=jonasbb a=jonasbb Co-authored-by: Jonas Bushart <jonas@bushart.org>
jonasbb · Jan 5, 2021 · 977bdd4 · 977bdd4
2 parents b7a09f5 + c911f26
commit 977bdd4
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Showing 4 changed files with 36 additions and 1 deletion.
diff --git a/serde_with_macros/Cargo.toml b/serde_with_macros/Cargo.toml
@@ -21,7 +21,7 @@ proc-macro = true
 maintenance = {status = "actively-developed"}
 
 [dependencies]
-darling = "0.11.0"
+darling = "0.12.0"
 proc-macro2 = "1.0.1"
 quote = "1.0.0"
 

diff --git a/serde_with_macros/src/lib.rs b/serde_with_macros/src/lib.rs
@@ -499,6 +499,7 @@ fn serde_as_add_attr_to_field(
     let serde_as_options = SerdeAsOptions::from_field(field)?;
     let serde_with_options = SerdeWithOptions::from_field(field)?;
 
+    // TODO allow multiple attributes
     // Find index of serde_as attribute
     let serde_as_idx = field.attrs.iter().enumerate().find_map(|(idx, attr)| {
         if attr.path.is_ident("serde_as") {
@@ -515,6 +516,10 @@ fn serde_as_add_attr_to_field(
     // serde_as Attribute
     field.attrs.remove(serde_as_idx);
 
+    if !serde_as_options.has_any_set() {
+        return Err(DarlingError::custom("An empty `serde_as` attribute on a field has no effect. You are missing an `as`, `serialize_as`, or `deserialize_as` parameter."));
+    }
+
     // Check if there are any conflicting attributes
     if serde_as_options.has_any_set() && serde_with_options.has_any_set() {
         return Err(DarlingError::custom("Cannot combine `serde_as` with serde's `with`, `deserialize_with`, or `serialize_with`."));

diff --git a/serde_with_macros/tests/compile-fail/serde_as.rs b/serde_with_macros/tests/compile-fail/serde_as.rs
@@ -60,4 +60,16 @@ struct ConflictingAsAnnotations {
     two_unkowns: u32,
 }
 
+/// Test error message for malformed attributes
+#[serde_as]
+#[derive(Serialize)]
+struct MalformedAttributes {
+    #[serde_as(serialize_as = "123", deserialize_as = DisplayFromStr)]
+    missing_quotes: u32,
+    #[serde_as]
+    no_entries: u32,
+    #[serde_as()]
+    no_entries_brackets: u32,
+}
+
 fn main() {}
diff --git a/serde_with_macros/tests/compile-fail/serde_as.stderr b/serde_with_macros/tests/compile-fail/serde_as.stderr
@@ -87,3 +87,21 @@ error: Unknown field: `unknw2`
    |
 59 |     #[serde_as(unknwn1 = "Hello", unknw2 = "World")]
    |                                   ^^^^^^
+
+error: Unable to parse attribute: expected literal
+  --> $DIR/serde_as.rs:67:55
+   |
+67 |     #[serde_as(serialize_as = "123", deserialize_as = DisplayFromStr)]
+   |                                                       ^^^^^^^^^^^^^^
+
+error: An empty `serde_as` attribute on a field has no effect. You are missing an `as`, `serialize_as`, or `deserialize_as` parameter.
+  --> $DIR/serde_as.rs:70:5
+   |
+70 |     no_entries: u32,
+   |     ^^^^^^^^^^
+
+error: An empty `serde_as` attribute on a field has no effect. You are missing an `as`, `serialize_as`, or `deserialize_as` parameter.
+  --> $DIR/serde_as.rs:72:5
+   |
+72 |     no_entries_brackets: u32,
+   |     ^^^^^^^^^^^^^^^^^^^