Improve SCIP symbols

In particular, the symbol generation before this change creates a lot
of symbols with the same name for different definitions. This change
makes progress on symbol uniqueness, but does not fix a couple cases
where it was unclear to me how to fix (see TODOs in `scip.rs`)

Behavior changes:

* `scip` command now reports symbol information omitted due to symbol
collisions. Iterating with this on a large codebase (Zed!) resulted in
the other improvements in this change.

* Generally fixes providing the path to nested definitions in
symbols. Instead of having special cases for a couple limited cases of
nesting, implements `Definition::enclosing_definition` and uses this
to walk definitions.

* Parameter variables are now treated like locals.

    - This fixes a bug where closure captures also received symbols
    scoped to the containing function.  To bring back parameter
    symbols I would want a way to filter these out, since they can
    cause symbol collisions.

    - Having symbols for them seems to be intentional in
    27e2eea54f, but no particular use is
    specified there. For the typical indexing purposes of SCIP I don't see
    why parameter symbols are useful or sensible, as function parameters
    are not referencable by anything but position. I can imagine they
    might be useful in representing diagnostics or something.

* Inherent impls are now represented as `impl#[SelfType]` - a type
named `impl` which takes a single type parameter.

* Trait impls are now represented as `impl#[SelfType][TraitType]` - a
type named `impl` which takes two type parameters.

* Associated types in traits and impls are now treated like types
instead of type parameters, and so are now suffixed with `#` instead
of wrapped with `[]`.  Treating them as type parameters seems to have
been intentional in 73d9c77f2a but it
doesn't make sense to me, so changing it.

* Static variables are now treated as terms instead of `Meta`, and so
receive `.` suffix instead of `:`.

* Attributes are now treated as `Meta` instead of `Macro`, and so
receive `:` suffix instead of `!`.

* `enclosing_symbol` is now provided for labels and generic params,
which are local symbols.

* Fixes a bug where presence of `'` causes a descriptor name to get
double wrapped in backticks, since both `fn new_descriptor` and
`scip::symbol::format_symbol` have logic for wrapping in
backticks. Solution is to simply delete the redundant logic.

* Deletes a couple tests in moniker.rs because the cases are
adequeately covered in scip.rs and the format for identifiers used in
moniker.rs is clunky with the new representation for trait impls

crates/ide-db/src/defs.rs

@@ -13,10 +13,10 @@ use either::Either;
 use hir::{
     Adt, AsAssocItem, AsExternAssocItem, AssocItem, AttributeTemplate, BuiltinAttr, BuiltinType,
     Const, Crate, DefWithBody, DeriveHelper, DocLinkDef, ExternAssocItem, ExternCrateDecl, Field,
-    Function, GenericParam, GenericSubstitution, HasVisibility, HirDisplay, Impl, InlineAsmOperand,
-    Label, Local, Macro, Module, ModuleDef, Name, PathResolution, Semantics, Static,
-    StaticLifetime, Struct, ToolModule, Trait, TraitAlias, TupleField, TypeAlias, Variant,
-    VariantDef, Visibility,
+    Function, GenericDef, GenericParam, GenericSubstitution, HasContainer, HasVisibility,
+    HirDisplay, Impl, InlineAsmOperand, ItemContainer, Label, Local, Macro, Module, ModuleDef,
+    Name, PathResolution, Semantics, Static, StaticLifetime, Struct, ToolModule, Trait, TraitAlias,
+    TupleField, TypeAlias, Variant, VariantDef, Visibility,
 };
 use span::Edition;
 use stdx::{format_to, impl_from};
@@ -98,8 +98,30 @@ impl Definition {
 
     pub fn enclosing_definition(&self, db: &RootDatabase) -> Option<Definition> {
         match self {
+            Definition::Macro(it) => Some(it.module(db).into()),
+            Definition::Module(it) => it.parent(db).map(Definition::Module),
+            Definition::Field(it) => Some(it.parent_def(db).into()),
+            Definition::Function(it) => it.container(db).try_into().ok(),
+            Definition::Adt(it) => Some(it.module(db).into()),
+            Definition::Const(it) => it.container(db).try_into().ok(),
+            Definition::Static(it) => it.container(db).try_into().ok(),
+            Definition::Trait(it) => it.container(db).try_into().ok(),
+            Definition::TraitAlias(it) => it.container(db).try_into().ok(),
+            Definition::TypeAlias(it) => it.container(db).try_into().ok(),
+            Definition::Variant(it) => Some(Adt::Enum(it.parent_enum(db)).into()),
+            Definition::SelfType(it) => Some(it.module(db).into()),
             Definition::Local(it) => it.parent(db).try_into().ok(),
-            _ => None,
+            Definition::GenericParam(it) => Some(it.parent().into()),
+            Definition::Label(it) => it.parent(db).try_into().ok(),
+            Definition::ExternCrateDecl(it) => it.container(db).try_into().ok(),
+            Definition::DeriveHelper(it) => Some(it.derive().module(db).into()),
+            Definition::InlineAsmOperand(it) => it.parent(db).try_into().ok(),
+            Definition::BuiltinAttr(_)
+            | Definition::BuiltinType(_)
+            | Definition::BuiltinLifetime(_)
+            | Definition::TupleField(_)
+            | Definition::ToolModule(_)
+            | Definition::InlineAsmRegOrRegClass(_) => None,
         }
     }
 
@@ -932,3 +954,29 @@ impl TryFrom<DefWithBody> for Definition {
         }
     }
 }
+
+impl TryFrom<ItemContainer> for Definition {
+    type Error = ();
+    fn try_from(container: ItemContainer) -> Result<Self, Self::Error> {
+        match container {
+            ItemContainer::Trait(it) => Ok(it.into()),
+            ItemContainer::Impl(it) => Ok(it.into()),
+            ItemContainer::Module(it) => Ok(it.into()),
+            ItemContainer::ExternBlock() | ItemContainer::Crate(_) => Err(()),
+        }
+    }
+}
+
+impl From<GenericDef> for Definition {
+    fn from(def: GenericDef) -> Self {
+        match def {
+            GenericDef::Function(it) => it.into(),
+            GenericDef::Adt(it) => it.into(),
+            GenericDef::Trait(it) => it.into(),
+            GenericDef::TraitAlias(it) => it.into(),
+            GenericDef::TypeAlias(it) => it.into(),
+            GenericDef::Impl(it) => it.into(),
+            GenericDef::Const(it) => it.into(),
+        }
+    }
+}