implement string context

fix-vm/src/instructions/arithmetic.rs

@@ -33,7 +33,13 @@ impl<'gc> crate::Vm<'gc> {
             return Step::Continue(());
         }
         if let (Some(ls), Some(rs)) = (ctx.get_string(lhs), ctx.get_string_or_path(rhs)) {
-            let ns = Gc::new(mc, crate::NixString::new(format!("{ls}{rs}")));
+            let merged = ctx
+                .get_string_context(lhs)
+                .merge(ctx.get_string_context(rhs));
+            let ns = Gc::new(
+                mc,
+                crate::NixString::with_context(format!("{ls}{rs}"), merged),
+            );
             self.push(Value::new_gc(ns));
             return Step::Continue(());
         }

fix-vm/src/instructions/misc.rs

@@ -1,6 +1,8 @@
 use std::path::PathBuf;
 
-use fix_abstract_vm::{AttrSet, NixString, Path, StrictValue, canon_path_str};
+use fix_abstract_vm::{
+    AttrSet, NixString, Path, StrictValue, StringContext, canon_path_str
+};
 use fix_builtins::BuiltinId;
 use fix_common::StringId;
 use fix_error::Error;
@@ -89,29 +91,45 @@ impl<'gc> crate::Vm<'gc> {
         &mut self,
         ctx: &mut impl VmRuntimeCtx,
         reader: &mut BytecodeReader<'_>,
-        _mc: &gc_arena::Mutation<'gc>,
+        mc: &gc_arena::Mutation<'gc>,
     ) -> Step {
         let count = reader.read_u16() as usize;
         let _force_string = reader.read_u8() != 0;
 
         let mut total_len = 0;
+        let mut has_any_context = false;
         for i in 0..count {
             let val = self.peek_forced(count - 1 - i);
             let s = ctx.get_string(val).expect("coerced");
             total_len += s.len();
+            if !ctx.get_string_context(val).is_empty() {
+                has_any_context = true;
+            }
         }
 
         let mut result = String::with_capacity(total_len);
+        let mut merged = StringContext::new();
         for i in 0..count {
             let val = self.peek_forced(count - 1 - i);
             let s = ctx.get_string(val).expect("coerced");
             result.push_str(s);
+            if has_any_context {
+                let ctx = ctx.get_string_context(val);
+                if !ctx.is_empty() {
+                    merged = merged.merge(ctx);
+                }
+            }
         }
 
         self.stack.truncate(self.stack.len() - count);
 
-        let sid = ctx.intern_string(result);
-        self.push(Value::new_inline(sid));
+        if merged.is_empty() {
+            let sid = ctx.intern_string(result);
+            self.push(Value::new_inline(sid));
+        } else {
+            let ns = gc_arena::Gc::new(mc, NixString::with_context(result, merged));
+            self.push(Value::new_gc(ns));
+        }
         Step::Continue(())
     }