Make string literals owned wherever Rust receives a String [patch]

[matt-edmondson]

Fixes #154

What was wrong

#120 added String::from("…"), but only for the return-statement and typed-local paths. Every other place an owned String receives a string literal still wrote a bare &str, and rustc rejected it with E0308: mismatched types (expected String, found &str):

pub const DEFAULT: String = "d";
Self { name: "Anon", nickname: "none" }
return Person { name: "x", nickname: "y" };
self.name = "y";
return (if c { "a" } else { "b" });
pub const NAMES: &[String] = &[ "a", "b" ];

Change (all in RustGenerator)

• Struct literals: each named field is written through WriteValue using the field's declared type. That covers a constructor's initialisers, a field's declared starting value (which the constructor fills in), and a ConstructionExpression naming the struct. The struct is constructedType for Self, or for its own name inside its impl; otherwise it is looked up in the document with the existing DeclaredTypes(GenerationRoot).
• Assignment to self.<field>: GenerateAssignmentStatement writes the value using the field's declared type. Only plain = changes; String += "lit" already compiles.
• Conditionals: WriteValue now recurses into both branches of a ConditionalExpression when the target type is an owned String.
• Consts and statics: SpellStorageType spells a string as &'static str, and an array of them as &[&'static str]. String::from is not a const fn, so a constant can never hold a String built from a literal. The lifetime is written out because elision in associated consts is being phased out.

Output for the issue's repro now:

pub const DEFAULT: &'static str = "d";
Self { name: String::from("Anon"), nickname: String::from("none") }
return Person { name: String::from("x"), nickname: String::from("y") };
self.name = String::from("y");
return (if c { String::from("a") } else { String::from("b") });
pub const NAMES: &[&'static str] = &[ "a", "b" ];

Tests

• New RustGeneratedSourceCompilesTests.StringLiteralsFillingStringFieldsAndConstants_Compile. It covers the issue's repro plus a struct literal built outside the type's own impl, a field's declared starting value, a module-level const and static, and a string table. It compiles them with rustc --edition 2021.
• Before the change it failed with 13 E0308 errors. After the change it passes.
• Full Coder.Test suite: 1265 passed, 0 failed. dotnet format --verify-no-changes on the touched files reports only the CHARSET/IMPORTS findings that main already has.

Known limits

• A string constant is now &'static str. Code that reads such a constant where a String is expected (for example return Self::DEFAULT; from a function returning String) still needs a conversion. That is the same kind of bug in another position, but it is not one of the five this issue lists.
• A string constant whose initialiser is a call (not a literal) is also spelled &'static str. No reported case needs anything else, and String::from couldn't appear there anyway.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NW9fJSB9VKsuPv7M2UmznC

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

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