➖ Integrate "SmartDefault" as "AutoDefault" macro

helpers/pagetop-macros/src/smart_default/default_attr.rs

@@ -0,0 +1,89 @@
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::{parse::Error, MetaNameValue};
+
+use crate::smart_default::util::find_only;
+
+#[derive(Debug, Clone, Copy)]
+pub enum ConversionStrategy {
+    NoConversion,
+    Into,
+}
+
+pub struct DefaultAttr {
+    pub code: Option<TokenStream>,
+    conversion_strategy: Option<ConversionStrategy>,
+}
+
+impl DefaultAttr {
+    pub fn find_in_attributes(attrs: &[syn::Attribute]) -> Result<Option<Self>, Error> {
+        if let Some(default_attr) =
+            find_only(attrs.iter(), |attr| Ok(attr.path().is_ident("default")))?
+        {
+            match &default_attr.meta {
+                syn::Meta::Path(_) => Ok(Some(Self {
+                    code: None,
+                    conversion_strategy: None,
+                })),
+                syn::Meta::List(meta) => {
+                    // If the meta contains exactly (_code = "...") take the string literal as the
+                    // expression
+                    if let Ok(ParseCodeHack(code_hack)) = syn::parse(meta.tokens.clone().into()) {
+                        Ok(Some(Self {
+                            code: Some(code_hack),
+                            conversion_strategy: Some(ConversionStrategy::NoConversion),
+                        }))
+                    } else {
+                        Ok(Some(Self {
+                            code: Some(meta.tokens.clone()),
+                            conversion_strategy: None,
+                        }))
+                    }
+                }
+                syn::Meta::NameValue(MetaNameValue { value, .. }) => Ok(Some(Self {
+                    code: Some(value.into_token_stream()),
+                    conversion_strategy: None,
+                })),
+            }
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn conversion_strategy(&self) -> ConversionStrategy {
+        if let Some(conversion_strategy) = self.conversion_strategy {
+            // Conversion strategy already set
+            return conversion_strategy;
+        }
+        let code = if let Some(code) = &self.code {
+            code
+        } else {
+            // #[default] - so no conversion (`Default::default()` already has the correct type)
+            return ConversionStrategy::NoConversion;
+        };
+        match syn::parse::<syn::Lit>(code.clone().into()) {
+            Ok(syn::Lit::Str(_)) | Ok(syn::Lit::ByteStr(_)) => {
+                // A string literal - so we need a conversion in case we need to make it a `String`
+                return ConversionStrategy::Into;
+            }
+            _ => {}
+        }
+        // Not handled by one of the rules, so we don't convert it to avoid causing trouble
+        ConversionStrategy::NoConversion
+    }
+}
+
+struct ParseCodeHack(TokenStream);
+
+impl syn::parse::Parse for ParseCodeHack {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        let ident: syn::Ident = input.parse()?;
+        if ident != "_code" {
+            return Err(Error::new(ident.span(), "Expected `_code`"));
+        }
+        input.parse::<syn::token::Eq>()?;
+        let code: syn::LitStr = input.parse()?;
+        let code: TokenStream = code.parse()?;
+        Ok(ParseCodeHack(code))
+    }
+}