ir::asg::Object::Empty: Remove variant

This variant is unnecessary, as it was used only by the indexer to represent
the absence of a node, for which was can simply use `None` in the containing
`Option`.

* tamer/Cargo.toml: Add `lazy_static`.
* tamer/Cargo.lock: Update.
* tamer/src/ir/asg/base.rs (with_capacity): Use `None` in place of
    `Some(Object::Empty)`.
* tamer/src/ir/asg/object.rs: Adjust state machine graphic.
  (Empty): Remove variant.
  (Missing): Remove reference to variance.
* tamer/src/lib.rs: Import `lazy_static` for test builds.
* tamer/obj/xmle/writer/writer.rs (Section::iter): Remove `Object::Empty`
    from documentation.
  (test::): Remove references to `Object::Missing`.  `lazy_static!` used
    here.
* tamer/obj/xmle/writer/xmle.rs (test::write_section_catch_missing): Replace
    reference to `Object::Missing`.

tamer/Cargo.lock

@@ -243,6 +243,7 @@ dependencies = [
  "fixedbitset 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "fxhash 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "getopts 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "petgraph 0.4.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "predicates 1.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "quick-xml 0.17.0 (registry+https://github.com/rust-lang/crates.io-index)",

tamer/Cargo.toml

@@ -35,4 +35,5 @@ petgraph = ">= 0.4.13"
 quick-xml = ">= 0.17.0"
 getopts = "0.2"
 exitcode = "1.1.2"
+lazy_static = ">= 1.4.0"
 

tamer/src/ir/asg/base.rs

@@ -81,7 +81,7 @@ where
         let mut index = Vec::with_capacity(objects);
 
         // Exhaust the first index to be used as a placeholder.
-        let empty_node = graph.add_node(Some(Object::Empty));
+        let empty_node = graph.add_node(None);
         index.push(empty_node);
 
         Self {

tamer/src/ir/asg/object.rs

@@ -31,19 +31,11 @@ use crate::sym::Symbol;
 /// These types represent object states:
 ///
 /// ```text
-///       ,-> (Missing) -------.
-///      /         \            \
-///     /           v            v
-/// ((Empty)) -> (Extern) -> ((Ident)) -> ((IdentFragment)).
+/// (Missing) -> (Extern) -> ((Ident)) -> ((IdentFragment)).
 ///     \                        ^               /
 ///      \                      / \             /
 ///       `--------------------`   `-----------'
 /// ```
-///
-/// The [`Empty`][Object::Empty] state is never directly accessable
-///   through [`Asg`][super::Asg]'s public API,
-///     as it represents the _absence_ of an object at that node within the
-///     ASG.
 #[derive(Debug, PartialEq)]
 pub enum Object<'i> {
     /// An identifier is expected to be defined but is not yet available.
@@ -53,8 +45,6 @@ pub enum Object<'i> {
     /// By defining an object as missing,
     ///   this allows the graph to be built incrementally as objects are
     ///   discovered.
-    ///
-    /// Note that this is different than [`Empty`][Object::Empty].
     Missing(&'i Symbol<'i>),
 
     /// A resolved identifier.
@@ -79,13 +69,6 @@ pub enum Object<'i> {
     ///   [linker][crate::ld] to put them into the correct order for the
     ///   final executable.
     IdentFragment(&'i Symbol<'i>, IdentKind, Source<'i>, FragmentText),
-
-    /// The empty node (default value for indexer).
-    ///
-    /// This is not a valid state accessible via [`Asg`][super::Asg].
-    ///
-    /// Note that this is different than [`Missing`][Object::Missing].
-    Empty,
 }
 
 /// Compiled fragment for identifier.

tamer/src/ir/asg/section.rs

@@ -83,9 +83,11 @@ impl<'a, 'i> Section<'a, 'i> {
     ///
     /// ```
     /// use tamer::ir::asg::{Object, Section};
+    /// use tamer::sym::{DefaultInterner, Interner};
     ///
+    /// let interner = DefaultInterner::new();
     /// let mut section = Section::new();
-    /// let obj = Object::Empty;
+    /// let obj = Object::Missing(interner.intern("ident"));
     /// let expect = vec![&obj, &obj, &obj];
     ///
     /// section.push_head(&obj);
@@ -166,6 +168,12 @@ impl<'a, 'i> Sections<'a, 'i> {
 #[cfg(test)]
 mod test {
     use super::*;
+    use crate::sym::{Symbol, SymbolIndex};
+
+    lazy_static! {
+        static ref SYM: Symbol<'static> =
+            Symbol::new_dummy(SymbolIndex::from_u32(1), "sym");
+    }
 
     #[test]
     fn section_empty() {
@@ -179,7 +187,7 @@ mod test {
     #[test]
     fn section_head() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
 
         assert!(section.head.is_empty());
 
@@ -191,7 +199,7 @@ mod test {
     #[test]
     fn section_body() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
 
         assert!(section.body.is_empty());
 
@@ -204,7 +212,7 @@ mod test {
     #[test]
     fn section_tail() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
 
         assert!(section.tail.is_empty());
 
@@ -216,7 +224,7 @@ mod test {
     #[test]
     fn section_len() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
 
         assert_eq!(0, section.len());
         section.push_head(&obj);
@@ -230,7 +238,7 @@ mod test {
     #[test]
     fn section_is_empty_head() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
 
         assert!(section.is_empty());
         section.push_head(&obj);
@@ -240,7 +248,7 @@ mod test {
     #[test]
     fn section_is_empty_body() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
 
         assert!(section.is_empty());
         section.push_body(&obj);
@@ -250,7 +258,7 @@ mod test {
     #[test]
     fn section_is_empty_tail() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
 
         assert!(section.is_empty());
         section.push_tail(&obj);
@@ -260,7 +268,7 @@ mod test {
     #[test]
     fn section_iterator() {
         let mut section = Section::new();
-        let obj = Object::Empty;
+        let obj = Object::Missing(&SYM);
         let expect = vec![&obj, &obj, &obj];
 
         section.push_head(&obj);

tamer/src/lib.rs

@@ -25,5 +25,9 @@ pub mod ld;
 pub mod obj;
 pub mod sym;
 
+#[cfg(test)]
+#[macro_use]
+extern crate lazy_static;
+
 #[cfg(test)]
 pub mod test;

tamer/src/obj/xmle/writer/xmle.rs

@@ -546,7 +546,8 @@ mod test {
             panic!("callback should not have been called");
         }));
 
-        let obj = Object::Empty;
+        let sym = Symbol::new_dummy(SymbolIndex::from_u32(1), "sym");
+        let obj = Object::Missing(&sym);
 
         let mut section = Section::new();
         section.push_body(&obj);