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rust: qemu_api_macros: make pattern matching more readable and efficient

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"let ... else" is useful when visiting syntax trees; it avoids multiple
levels of indentation and places the error close to the pattern.

While at it, use "ref" to avoid moving the syntax tree objects.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2025-05-02 11:42:48 +02:00
parent 51209c2aed
commit 465a4b80e2
1 changed files with 37 additions and 47 deletions
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84
rust/qemu-api-macros/src/lib.rs
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@ -16,50 +16,41 @@ fn get_fields<'a>(
input: &'a DeriveInput, input: &'a DeriveInput,
msg: &str, msg: &str,
) -> Result<&'a Punctuated<Field, Comma>, MacroError> { ) -> Result<&'a Punctuated<Field, Comma>, MacroError> {
if let Data::Struct(s) = &input.data { let Data::Struct(ref s) = &input.data else {
if let Fields::Named(fs) = &s.fields { return Err(MacroError::Message(
Ok(&fs.named)
} else {
Err(MacroError::Message(
format!("Named fields required for {}", msg),
input.ident.span(),
))
}
} else {
Err(MacroError::Message(
format!("Struct required for {}", msg), format!("Struct required for {}", msg),
input.ident.span(), input.ident.span(),
)) ));
} };
let Fields::Named(ref fs) = &s.fields else {
return Err(MacroError::Message(
format!("Named fields required for {}", msg),
input.ident.span(),
));
};
Ok(&fs.named)
} }
fn get_unnamed_field<'a>(input: &'a DeriveInput, msg: &str) -> Result<&'a Field, MacroError> { fn get_unnamed_field<'a>(input: &'a DeriveInput, msg: &str) -> Result<&'a Field, MacroError> {
if let Data::Struct(s) = &input.data { let Data::Struct(ref s) = &input.data else {
let unnamed = match &s.fields { return Err(MacroError::Message(
Fields::Unnamed(FieldsUnnamed {
unnamed: ref fields,
..
}) => fields,
_ => {
return Err(MacroError::Message(
format!("Tuple struct required for {}", msg),
s.fields.span(),
))
}
};
if unnamed.len() != 1 {
return Err(MacroError::Message(
format!("A single field is required for {}", msg),
s.fields.span(),
));
}
Ok(&unnamed[0])
} else {
Err(MacroError::Message(
format!("Struct required for {}", msg), format!("Struct required for {}", msg),
input.ident.span(), input.ident.span(),
)) ));
};
let Fields::Unnamed(FieldsUnnamed { ref unnamed, .. }) = &s.fields else {
return Err(MacroError::Message(
format!("Tuple struct required for {}", msg),
s.fields.span(),
));
};
if unnamed.len() != 1 {
return Err(MacroError::Message(
format!("A single field is required for {}", msg),
s.fields.span(),
));
} }
Ok(&unnamed[0])
} }
fn is_c_repr(input: &DeriveInput, msg: &str) -> Result<(), MacroError> { fn is_c_repr(input: &DeriveInput, msg: &str) -> Result<(), MacroError> {
@ -210,20 +201,19 @@ fn get_repr_uN(input: &DeriveInput, msg: &str) -> Result<Path, MacroError> {
} }
fn get_variants(input: &DeriveInput) -> Result<&Punctuated<Variant, Comma>, MacroError> { fn get_variants(input: &DeriveInput) -> Result<&Punctuated<Variant, Comma>, MacroError> {
if let Data::Enum(e) = &input.data { let Data::Enum(ref e) = &input.data else {
if let Some(v) = e.variants.iter().find(|v| v.fields != Fields::Unit) { return Err(MacroError::Message(
return Err(MacroError::Message(
"Cannot derive TryInto for enum with non-unit variants.".to_string(),
v.fields.span(),
));
}
Ok(&e.variants)
} else {
Err(MacroError::Message(
"Cannot derive TryInto for union or struct.".to_string(), "Cannot derive TryInto for union or struct.".to_string(),
input.ident.span(), input.ident.span(),
)) ));
};
if let Some(v) = e.variants.iter().find(|v| v.fields != Fields::Unit) {
return Err(MacroError::Message(
"Cannot derive TryInto for enum with non-unit variants.".to_string(),
v.fields.span(),
));
} }
Ok(&e.variants)
} }
#[rustfmt::skip::macros(quote)] #[rustfmt::skip::macros(quote)]