Add a container-level rename_all attribute to FromSql/ToSql.

It works both with composite types' fields and enum variants, although
arguably it will be the most useful for the latter as that's where
the naming conventions between Rust and a typical PostgreSQL schema differ.

Right now it supports the following casing styles:

* `"camelCase"`
* `"kebab-case"`
* `"lowercase"`
* `"PascalCase"`
* `"SCREAMING-KEBAB-CASE"`
* `"SCREAMING_SNAKE_CASE"`
* `"snake_case"`
* `"UPPERCASE"`

mimicking Serde.

postgres-derive-test/src/composites.rs

@@ -89,6 +89,48 @@ fn name_overrides() {
     );
 }
 
+#[test]
+fn rename_all_overrides() {
+    #[derive(FromSql, ToSql, Debug, PartialEq)]
+    #[postgres(name = "inventory_item", rename_all = "SCREAMING_SNAKE_CASE")]
+    struct InventoryItem {
+        name: String,
+        supplier_id: i32,
+        price: Option<f64>,
+    }
+
+    let mut conn = Client::connect("user=postgres host=localhost port=5433", NoTls).unwrap();
+    conn.batch_execute(
+        "CREATE TYPE pg_temp.inventory_item AS (
+            \"NAME\" TEXT,
+            \"SUPPLIER_ID\" INT,
+            \"PRICE\" DOUBLE PRECISION
+        );",
+    )
+    .unwrap();
+
+    let item = InventoryItem {
+        name: "foobar".to_owned(),
+        supplier_id: 100,
+        price: Some(15.50),
+    };
+
+    let item_null = InventoryItem {
+        name: "foobar".to_owned(),
+        supplier_id: 100,
+        price: None,
+    };
+
+    test_type(
+        &mut conn,
+        "inventory_item",
+        &[
+            (item, "ROW('foobar', 100, 15.50)"),
+            (item_null, "ROW('foobar', 100, NULL)"),
+        ],
+    );
+}
+
 #[test]
 fn wrong_name() {
     #[derive(FromSql, ToSql, Debug, PartialEq)]

postgres-derive-test/src/enums.rs

@@ -53,6 +53,35 @@ fn name_overrides() {
     );
 }
 
+#[test]
+fn rename_all_overrides() {
+    #[derive(Debug, ToSql, FromSql, PartialEq)]
+    #[postgres(name = "mood", rename_all = "snake_case")]
+    enum Mood {
+        Sad,
+        #[postgres(name = "okay")]
+        Ok,
+        Happy,
+    }
+
+    let mut conn = Client::connect("user=postgres host=localhost port=5433", NoTls).unwrap();
+    conn.execute(
+        "CREATE TYPE pg_temp.mood AS ENUM ('sad', 'okay', 'happy')",
+        &[],
+    )
+    .unwrap();
+
+    test_type(
+        &mut conn,
+        "mood",
+        &[
+            (Mood::Sad, "'sad'"),
+            (Mood::Ok, "'okay'"),
+            (Mood::Happy, "'happy'"),
+        ],
+    );
+}
+
 #[test]
 fn wrong_name() {
     #[derive(Debug, ToSql, FromSql, PartialEq)]

postgres-derive/Cargo.toml

@@ -12,6 +12,10 @@ proc-macro = true
 test = false
 
 [dependencies]
+convert_case = "0.6"
+itertools = "0.10"
 syn = "1.0"
 proc-macro2 = "1.0"
+strum = "0.24"
+strum_macros = "0.24"
 quote = "1.0"

postgres-derive/src/composites.rs

@@ -4,7 +4,7 @@ use syn::{
     TypeParamBound,
 };
 
-use crate::overrides::Overrides;
+use crate::{field_variant_overrides::FieldVariantOverrides, struct_overrides::StructOverrides};
 
 pub struct Field {
     pub name: String,
@@ -13,17 +13,20 @@ pub struct Field {
 }
 
 impl Field {
-    pub fn parse(raw: &syn::Field) -> Result<Field, Error> {
-        let overrides = Overrides::extract(&raw.attrs)?;
+    pub fn parse(struct_overrides: &StructOverrides, raw: &syn::Field) -> Result<Field, Error> {
+        use convert_case::Casing;
+
+        let mut overrides = FieldVariantOverrides::extract(&raw.attrs)?;
 
         let ident = raw.ident.as_ref().unwrap().clone();
         Ok(Field {
-            name: overrides.name.unwrap_or_else(|| {
+            name: overrides.name.take().unwrap_or_else(|| {
                 let name = ident.to_string();
-                match name.strip_prefix("r#") {
-                    Some(name) => name.to_string(),
-                    None => name,
-                }
+                let name = name.strip_prefix("r#").map(String::from).unwrap_or(name);
+                struct_overrides
+                    .rename_all
+                    .map(|case| name.to_case(case))
+                    .unwrap_or(name)
             }),
             ident,
             type_: raw.ty.clone(),

postgres-derive/src/enums.rs

@@ -1,14 +1,16 @@
 use syn::{Error, Fields, Ident};
 
-use crate::overrides::Overrides;
+use crate::{field_variant_overrides::FieldVariantOverrides, struct_overrides::StructOverrides};
 
 pub struct Variant {
     pub ident: Ident,
     pub name: String,
 }
 
 impl Variant {
-    pub fn parse(raw: &syn::Variant) -> Result<Variant, Error> {
+    pub fn parse(struct_overrides: &StructOverrides, raw: &syn::Variant) -> Result<Variant, Error> {
+        use convert_case::Casing;
+
         match raw.fields {
             Fields::Unit => {}
             _ => {
@@ -19,10 +21,17 @@ impl Variant {
             }
         }
 
-        let overrides = Overrides::extract(&raw.attrs)?;
+        let mut overrides = FieldVariantOverrides::extract(&raw.attrs)?;
         Ok(Variant {
             ident: raw.ident.clone(),
-            name: overrides.name.unwrap_or_else(|| raw.ident.to_string()),
+            name: overrides.name.take().unwrap_or_else(|| {
+                let name = raw.ident.to_string();
+                let name = name.strip_prefix("r#").map(String::from).unwrap_or(name);
+                struct_overrides
+                    .rename_all
+                    .map(|case| name.to_case(case))
+                    .unwrap_or(name)
+            }),
         })
     }
 }

postgres-derive/src/field_variant_overrides.rs

@@ -0,0 +1,49 @@
+use syn::{Attribute, Error, Lit, Meta, NestedMeta};
+
+#[derive(Default)]
+pub struct FieldVariantOverrides {
+    pub name: Option<String>,
+}
+
+impl FieldVariantOverrides {
+    pub fn extract(attrs: &[Attribute]) -> Result<FieldVariantOverrides, Error> {
+        let mut overrides: FieldVariantOverrides = Default::default();
+
+        for attr in attrs {
+            let attr = attr.parse_meta()?;
+
+            if !attr.path().is_ident("postgres") {
+                continue;
+            }
+
+            let list = match attr {
+                Meta::List(ref list) => list,
+                bad => return Err(Error::new_spanned(bad, "expected a #[postgres(...)]")),
+            };
+
+            for item in &list.nested {
+                match item {
+                    NestedMeta::Meta(Meta::NameValue(meta)) => {
+                        if meta.path.is_ident("name") {
+                            let value = match &meta.lit {
+                                Lit::Str(s) => s.value(),
+                                bad => {
+                                    return Err(Error::new_spanned(
+                                        bad,
+                                        "expected a string literal",
+                                    ))
+                                }
+                            };
+                            overrides.name = Some(value);
+                        } else {
+                            return Err(Error::new_spanned(&meta.path, "unknown override"));
+                        }
+                    }
+                    bad => return Err(Error::new_spanned(bad, "unknown attribute")),
+                }
+            }
+        }
+
+        Ok(overrides)
+    }
+}

postgres-derive/src/fromsql.rs

@@ -12,10 +12,10 @@ use crate::accepts;
 use crate::composites::Field;
 use crate::composites::{append_generic_bound, new_derive_path};
 use crate::enums::Variant;
-use crate::overrides::Overrides;
+use crate::struct_overrides::StructOverrides;
 
 pub fn expand_derive_fromsql(input: DeriveInput) -> Result<TokenStream, Error> {
-    let overrides = Overrides::extract(&input.attrs)?;
+    let mut overrides = StructOverrides::extract(&input.attrs)?;
 
     if overrides.name.is_some() && overrides.transparent {
         return Err(Error::new_spanned(
@@ -24,7 +24,10 @@ pub fn expand_derive_fromsql(input: DeriveInput) -> Result<TokenStream, Error> {
         ));
     }
 
-    let name = overrides.name.unwrap_or_else(|| input.ident.to_string());
+    let name = overrides
+        .name
+        .take()
+        .unwrap_or_else(|| input.ident.to_string());
 
     let (accepts_body, to_sql_body) = if overrides.transparent {
         match input.data {
@@ -51,7 +54,7 @@ pub fn expand_derive_fromsql(input: DeriveInput) -> Result<TokenStream, Error> {
             let variants = data
                 .variants
                 .iter()
-                .map(Variant::parse)
+                .map(|variant| Variant::parse(&overrides, variant))
                 .collect::<Result<Vec<_>, _>>()?;
             (
                 accepts::enum_body(&name, &variants),
@@ -75,7 +78,7 @@ pub fn expand_derive_fromsql(input: DeriveInput) -> Result<TokenStream, Error> {
             let fields = fields
                 .named
                 .iter()
-                .map(Field::parse)
+                .map(|field| Field::parse(&overrides, field))
                 .collect::<Result<Vec<_>, _>>()?;
             (
                 accepts::composite_body(&name, "FromSql", &fields),

postgres-derive/src/lib.rs

@@ -9,8 +9,10 @@ use syn::parse_macro_input;
 mod accepts;
 mod composites;
 mod enums;
+mod field_variant_overrides;
 mod fromsql;
-mod overrides;
+mod rename_rule;
+mod struct_overrides;
 mod tosql;
 
 #[proc_macro_derive(ToSql, attributes(postgres))]

postgres-derive/src/rename_rule.rs

@@ -0,0 +1,36 @@
+use strum_macros::{Display, EnumIter, EnumString};
+
+#[derive(Clone, Copy, Display, EnumIter, EnumString)]
+pub enum RenameRule {
+    #[strum(serialize = "camelCase")]
+    Camel,
+    #[strum(serialize = "kebab-case")]
+    Kebab,
+    #[strum(serialize = "lowercase")]
+    Lower,
+    #[strum(serialize = "PascalCase")]
+    Pascal,
+    #[strum(serialize = "SCREAMING-KEBAB-CASE")]
+    ScreamingKebab,
+    #[strum(serialize = "SCREAMING_SNAKE_CASE")]
+    ScreamingSnake,
+    #[strum(serialize = "snake_case")]
+    Snake,
+    #[strum(serialize = "UPPERCASE")]
+    Upper,
+}
+
+impl From<RenameRule> for convert_case::Case {
+    fn from(rule: RenameRule) -> Self {
+        match rule {
+            RenameRule::Camel => Self::Camel,
+            RenameRule::Kebab => Self::Kebab,
+            RenameRule::Lower => Self::Lower,
+            RenameRule::Pascal => Self::Pascal,
+            RenameRule::ScreamingKebab => Self::UpperKebab,
+            RenameRule::ScreamingSnake => Self::UpperSnake,
+            RenameRule::Snake => Self::Snake,
+            RenameRule::Upper => Self::Upper,
+        }
+    }
+}