[PATCH proxmox v2] schema: api_string_type: impl FromStr to avoid allocating in error path

[Gabriel Goller <g.goller@proxmox.com>]

The existing from_string takes ownership of a String, meaning callers
with a &str had to heap-allocate first and discard the allocation on
validation failure. The new FromStr implementation validates the &str
against the schema's check_constraints before calling to_string(), so no
allocation happens on the error path.

Suggested-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
---

Changelog:
v2:
 - implemented FromStr trait instead of simple from_str method

 proxmox-schema/src/api_type_macros.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/proxmox-schema/src/api_type_macros.rs b/proxmox-schema/src/api_type_macros.rs
index f3740d14fd35..4f2e54d4e63e 100644
--- a/proxmox-schema/src/api_type_macros.rs
+++ b/proxmox-schema/src/api_type_macros.rs
@@ -21,6 +21,7 @@
 /// * `Display` as a pass-through to `String`'s `Display`
 /// * `Deref`
 /// * `DerefMut`
+/// * `FromStr`
 /// * `AsRef<str>`
 /// * `TryFrom<String>`
 /// * `fn into_string(self) -> String`
@@ -68,6 +69,19 @@ macro_rules! api_string_type {
             }
         }
 
+        impl ::std::str::FromStr for $name {
+            type Err = ::anyhow::Error;
+
+            fn from_str(inner: &str) -> Result<Self, Self::Err> {
+                use $crate::ApiType;
+                match &Self::API_SCHEMA {
+                    $crate::Schema::String(s) => s.check_constraints(inner)?,
+                    _ => unreachable!(),
+                }
+                Ok(Self(inner.to_string()))
+            }
+        }
+
         impl $name {
             /// Get the contained string.
             pub fn into_string(self) -> String {
-- 
2.47.3