cmd/compile/internal/noder: stub type section and adjust others

The type definition and object definition sections have nearly the same
structure - help illustrate that through consistent naming.

Change-Id: Ibed374fca4883a293a7fc16b36034e1acb38362a
Reviewed-on: https://go-review.googlesource.com/c/go/+/677378
Auto-Submit: Mark Freeman <mark@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/noder/doc.go

@@ -26,7 +26,7 @@ determines its index in the series.
                   SectionPosBase
                   SectionPkg
                   SectionName
-                  SectionType    // TODO(markfreeman) Define.
+                  SectionType
                   SectionObj
                   SectionObjExt  // TODO(markfreeman) Define.
                   SectionObjDict // TODO(markfreeman) Define.
@@ -137,6 +137,44 @@ Note, a PkgRef is *not* equivalent to Ref[Pkg] due to an extra marker.
                  Ref[Pkg]
                  .
 
+## Type Section
+The type section is a series of type definition elements.
+
+    SectionType = { TypeDef } .
+
+A type definition can be in one of several formats, which are identified
+by their TypeSpec code.
+
+    TypeDef     = RefTable
+                  [ Sync ]
+                  [ Sync ]
+                  Uint64            // denotes which TypeSpec to use
+                  TypeSpec
+                  .
+
+    TypeSpec    = TypeSpecBasic     // TODO(markfreeman): Define.
+                | TypeSpecNamed     // TODO(markfreeman): Define.
+                | TypeSpecPointer   // TODO(markfreeman): Define.
+                | TypeSpecSlice     // TODO(markfreeman): Define.
+                | TypeSpecArray     // TODO(markfreeman): Define.
+                | TypeSpecChan      // TODO(markfreeman): Define.
+                | TypeSpecMap       // TODO(markfreeman): Define.
+                | TypeSpecSignature // TODO(markfreeman): Define.
+                | TypeSpecStruct    // TODO(markfreeman): Define.
+                | TypeSpecInterface // TODO(markfreeman): Define.
+                | TypeSpecUnion     // TODO(markfreeman): Define.
+                | TypeSpecTypeParam // TODO(markfreeman): Define.
+                  .
+
+// TODO(markfreeman): Document the reader dictionary once we understand it more.
+To use a type elsewhere, a TypeUse is encoded.
+
+    TypeUse     = [ Sync ]
+                  Bool              // whether it is a derived type
+                  [ Uint64 ]        // if derived, an index into the reader dictionary
+                  [ Ref[TypeDef] ]  // else, a reference to the type
+                  .
+
 ## Object Sections
 Information about an object (e.g. variable, function, type name, etc.)
 is split into multiple elements in different sections. Those elements
@@ -160,22 +198,36 @@ for objects.
                   .
 
 ### Definition Section
-The definition section holds definitions for objects defined by the
-target package; it does not contain definitions for imported objects.
+The definition section holds definitions for objects defined by the target
+package; it does not contain definitions for imported objects.
 
     SectionObj = { ObjectDef } .
 
-Object definitions can be one of several formats. To determine the
-correct format, the name section must be referenced for the object's
-type.
+Object definitions can be in one of several formats. To determine the correct
+format, the name section must be referenced; it contains a code indicating
+the object's type.
 
-    ObjectDef = ObjectDefConst     // TODO(markfreeman) Define.
-              | ObjectDefFunc      // TODO(markfreeman) Define.
-              | ObjectDefAlias     // TODO(markfreeman) Define.
-              | ObjectDefNamedType // TODO(markfreeman) Define.
-              | ObjectDefVar       // TODO(markfreeman) Define.
+    ObjectDef = RefTable
+                [ Sync ]
+                ObjectSpec
                 .
 
+    ObjectSpec = ObjectSpecConst     // TODO(markfreeman) Define.
+               | ObjectSpecFunc      // TODO(markfreeman) Define.
+               | ObjectSpecAlias     // TODO(markfreeman) Define.
+               | ObjectSpecNamedType // TODO(markfreeman) Define.
+               | ObjectSpecVar       // TODO(markfreeman) Define.
+                 .
+
+To use an object definition elsewhere, an ObjectUse is encoded.
+
+    ObjectUse  = [ Sync ]
+                 [ Bool ]
+                 Ref[ObjectDef]
+                 Uint64              // the number of type arguments
+                 { TypeUse }         // references to the type arguments
+                 .
+
 # References
 A reference table precedes every element. Each entry in the table
 contains a (section, index) pair denoting the location of the
@@ -193,10 +245,15 @@ referenced element.
 Elements encode references to other elements as an index in the
 reference table — not the location of the referenced element directly.
 
-    // TODO(markfreeman): Rename to RefUse.
-    UseReloc = [ Sync ]
-               RelElemIdx
-               .
+    RefTableIdx   = Uint64 .
+
+To do this, the Ref[T] primitive is used as below; note that this is
+the same shape as provided by package pkgbits, just with new
+interpretation applied.
+
+    Ref[T]        = [ Sync ]
+                    RefTableIdx       // the Uint64
+                    .
 
 # Primitives
 Primitive encoding is handled separately by the pkgbits package. Check