Streamlined derivation of new Dialect objects

Author: alexander-beedie

Cargo.toml

@@ -42,6 +42,8 @@ std = []
 recursive-protection = ["std", "recursive"]
 # Enable JSON output in the `cli` example:
 json_example = ["serde_json", "serde"]
+# Enable derive macros for custom dialect creation
+derive-dialect = ["sqlparser_derive"]
 visitor = ["sqlparser_derive"]
 
 [dependencies]
@@ -61,6 +63,10 @@ simple_logger = "5.0"
 matches = "0.1"
 pretty_assertions = "1"
 
+[[test]]
+name = "sqlparser_derive_dialect"
+required-features = ["derive-dialect"]
+
 [package.metadata.docs.rs]
 # Document these features on docs.rs
-features = ["serde", "visitor"]
+features = ["serde", "visitor", "derive-dialect"]

derive/Cargo.toml

@@ -36,6 +36,6 @@ edition = "2021"
 proc-macro = true
 
 [dependencies]
-syn = { version = "2.0", default-features = false, features = ["printing", "parsing", "derive", "proc-macro"] }
+syn = { version = "2.0", default-features = false, features = ["full", "printing", "parsing", "derive", "proc-macro", "clone-impls"] }
 proc-macro2 = "1.0"
 quote = "1.0"

derive/src/dialect.rs

@@ -0,0 +1,310 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Implementation of the `derive_dialect!` macro for creating custom SQL dialects.
+
+use proc_macro2::TokenStream;
+use quote::{quote, quote_spanned};
+use std::collections::HashSet;
+use syn::{
+    braced,
+    parse::{Parse, ParseStream},
+    Error, File, FnArg, Ident, Item, LitBool, LitChar, Pat, ReturnType, Signature, Token,
+    TraitItem, Type,
+};
+
+/// Override value types supported by the macro
+pub(crate) enum Override {
+    Bool(LitBool),
+    Char(LitChar),
+    None,
+}
+
+/// Parsed input for the `derive_dialect!` macro
+pub(crate) struct DeriveDialectInput {
+    pub name: Ident,
+    pub base: Type,
+    pub preserve_type_id: bool,
+    pub overrides: Vec<(Ident, Override)>,
+}
+
+/// Information about a Dialect trait method
+struct DialectMethod {
+    name: Ident,
+    signature: Signature,
+}
+
+impl Parse for DeriveDialectInput {
+    fn parse(input: ParseStream) -> syn::Result<Self> {
+        let name: Ident = input.parse()?;
+        input.parse::<Token![,]>()?;
+        let base: Type = input.parse()?;
+
+        let mut preserve_type_id = false;
+        let mut overrides = Vec::new();
+
+        while input.peek(Token![,]) {
+            input.parse::<Token![,]>()?;
+            if input.is_empty() {
+                break;
+            }
+            if input.peek(Ident) {
+                let ident: Ident = input.parse()?;
+                match ident.to_string().as_str() {
+                    "preserve_type_id" => {
+                        input.parse::<Token![=]>()?;
+                        preserve_type_id = input.parse::<LitBool>()?.value();
+                    }
+                    "overrides" => {
+                        input.parse::<Token![=]>()?;
+                        let content;
+                        braced!(content in input);
+                        while !content.is_empty() {
+                            let key: Ident = content.parse()?;
+                            content.parse::<Token![=]>()?;
+                            let value = if content.peek(LitBool) {
+                                Override::Bool(content.parse()?)
+                            } else if content.peek(LitChar) {
+                                Override::Char(content.parse()?)
+                            } else if content.peek(Ident) {
+                                let ident: Ident = content.parse()?;
+                                if ident == "None" {
+                                    Override::None
+                                } else {
+                                    return Err(Error::new(
+                                        ident.span(),
+                                        format!("Expected `true`, `false`, a char, or `None`, found `{ident}`"),
+                                    ));
+                                }
+                            } else {
+                                return Err(
+                                    content.error("Expected `true`, `false`, a char, or `None`")
+                                );
+                            };
+                            overrides.push((key, value));
+                            if content.peek(Token![,]) {
+                                content.parse::<Token![,]>()?;
+                            }
+                        }
+                    }
+                    other => {
+                        return Err(Error::new(ident.span(), format!(
+                            "Unknown argument `{other}`. Expected `preserve_type_id` or `overrides`."
+                        )));
+                    }
+                }
+            }
+        }
+        Ok(DeriveDialectInput {
+            name,
+            base,
+            preserve_type_id,
+            overrides,
+        })
+    }
+}
+
+/// Entry point for the `derive_dialect!` procedural macro
+pub(crate) fn derive_dialect(input: DeriveDialectInput) -> proc_macro::TokenStream {
+    let err = |msg: String| {
+        Error::new(proc_macro2::Span::call_site(), msg)
+            .to_compile_error()
+            .into()
+    };
+
+    let source = match read_dialect_mod_file() {
+        Ok(s) => s,
+        Err(e) => return err(format!("Failed to read dialect/mod.rs: {e}")),
+    };
+    let file: File = match syn::parse_str(&source) {
+        Ok(f) => f,
+        Err(e) => return err(format!("Failed to parse source: {e}")),
+    };
+    let methods = match extract_dialect_methods(&file) {
+        Ok(m) => m,
+        Err(e) => return e.to_compile_error().into(),
+    };
+
+    // Validate overrides
+    let bool_names: HashSet<_> = methods
+        .iter()
+        .filter(|m| is_bool_method(&m.signature))
+        .map(|m| m.name.to_string())
+        .collect();
+    for (key, value) in &input.overrides {
+        let key_str = key.to_string();
+        let err = |msg| Error::new(key.span(), msg).to_compile_error().into();
+        match value {
+            Override::Bool(_) if !bool_names.contains(&key_str) => {
+                return err(format!("Unknown boolean method `{key_str}`"));
+            }
+            Override::Char(_) | Override::None if key_str != "identifier_quote_style" => {
+                return err(format!(
+                    "Char/None only valid for `identifier_quote_style`, not `{key_str}`"
+                ));
+            }
+            _ => {}
+        }
+    }
+    generate_derived_dialect(&input, &methods).into()
+}
+
+/// Generate the complete derived dialect implementation
+fn generate_derived_dialect(input: &DeriveDialectInput, methods: &[DialectMethod]) -> TokenStream {
+    let name = &input.name;
+    let base = &input.base;
+
+    // Helper to find an override by method name
+    let find_override = |method_name: &str| {
+        input
+            .overrides
+            .iter()
+            .find(|(k, _)| k == method_name)
+            .map(|(_, v)| v)
+    };
+
+    // Helper to generate delegation to base dialect
+    let delegate = |method: &DialectMethod| {
+        let sig = &method.signature;
+        let method_name = &method.name;
+        let params = extract_param_names(sig);
+        quote_spanned! { method_name.span() => #sig { self.dialect.#method_name(#(#params),*) } }
+    };
+
+    // Generate the struct
+    let struct_def = quote_spanned! { name.span() =>
+        #[derive(Debug)]
+        pub struct #name {
+            dialect: #base,
+        }
+        impl Default for #name {
+            fn default() -> Self {
+                Self { dialect: <#base>::default() }
+            }
+        }
+        impl #name {
+            pub fn new() -> Self { Self::default() }
+        }
+    };
+
+    // Generate TypeId method body
+    let type_id_body = if input.preserve_type_id {
+        quote! { Dialect::dialect(&self.dialect) }
+    } else {
+        quote! { ::core::any::TypeId::of::<#name>() }
+    };
+
+    // Generate method implementations
+    let method_impls = methods.iter().map(|method| {
+        let method_name = &method.name;
+        match find_override(&method_name.to_string()) {
+            Some(Override::Bool(value)) => {
+                quote_spanned! { method_name.span() => fn #method_name(&self) -> bool { #value } }
+            }
+            Some(Override::Char(c)) => {
+                quote_spanned! { method_name.span() =>
+                    fn identifier_quote_style(&self, _: &str) -> Option<char> { Some(#c) }
+                }
+            }
+            Some(Override::None) => {
+                quote_spanned! { method_name.span() =>
+                    fn identifier_quote_style(&self, _: &str) -> Option<char> { None }
+                }
+            }
+            None => delegate(method),
+        }
+    });
+
+    // Wrap impl in a const block with scoped imports so types resolve without qualification
+    quote! {
+        #struct_def
+        const _: () = {
+            use ::core::iter::Peekable;
+            use ::core::str::Chars;
+            use sqlparser::ast::{ColumnOption, Expr, GranteesType, Ident, ObjectNamePart, Statement};
+            use sqlparser::dialect::{Dialect, Precedence};
+            use sqlparser::keywords::Keyword;
+            use sqlparser::parser::{Parser, ParserError};
+
+            impl Dialect for #name {
+                fn dialect(&self) -> ::core::any::TypeId { #type_id_body }
+                #(#method_impls)*
+            }
+        };
+    }
+}
+
+/// Extract parameter names from a method signature (excluding self)
+fn extract_param_names(sig: &Signature) -> Vec<&Ident> {
+    sig.inputs
+        .iter()
+        .filter_map(|arg| match arg {
+            FnArg::Typed(pt) => match pt.pat.as_ref() {
+                Pat::Ident(pi) => Some(&pi.ident),
+                _ => None,
+            },
+            _ => None,
+        })
+        .collect()
+}
+
+/// Read the dialect/mod.rs file that contains the Dialect trait.
+fn read_dialect_mod_file() -> Result<String, String> {
+    let manifest_dir =
+        std::env::var("CARGO_MANIFEST_DIR").map_err(|_| "CARGO_MANIFEST_DIR not set")?;
+    let path = std::path::Path::new(&manifest_dir).join("src/dialect/mod.rs");
+    std::fs::read_to_string(&path).map_err(|e| format!("Failed to read {}: {e}", path.display()))
+}
+
+/// Extract all methods from the Dialect trait (excluding `dialect` for TypeId)
+fn extract_dialect_methods(file: &File) -> Result<Vec<DialectMethod>, Error> {
+    let dialect_trait = file
+        .items
+        .iter()
+        .find_map(|item| match item {
+            Item::Trait(t) if t.ident == "Dialect" => Some(t),
+            _ => None,
+        })
+        .ok_or_else(|| Error::new(proc_macro2::Span::call_site(), "Dialect trait not found"))?;
+
+    let mut methods: Vec<_> = dialect_trait
+        .items
+        .iter()
+        .filter_map(|item| match item {
+            TraitItem::Fn(m) if m.sig.ident != "dialect" => Some(DialectMethod {
+                name: m.sig.ident.clone(),
+                signature: m.sig.clone(),
+            }),
+            _ => None,
+        })
+        .collect();
+    methods.sort_by_key(|m| m.name.to_string());
+    Ok(methods)
+}
+
+/// Check if a method signature is `fn name(&self) -> bool`
+fn is_bool_method(sig: &Signature) -> bool {
+    sig.inputs.len() == 1
+        && matches!(
+            sig.inputs.first(),
+            Some(FnArg::Receiver(r)) if r.reference.is_some() && r.mutability.is_none()
+        )
+        && matches!(
+            &sig.output,
+            ReturnType::Type(_, ty) if matches!(ty.as_ref(), Type::Path(p) if p.path.is_ident("bool"))
+        )
+}