[dev.typeparams] cmd/compile/internal/noder: refactor irgen import handling

Rather than re-parsing and re-resolving the import path string, use
the PkgName object provided by types2 to determine what package path
it refers to.

Also, decompose importfile into smaller functions, so that we can
directly pass the already-resolved package path to the importer.

Finally, switch to simply using height as calculated by types2 rather
than redoing the calculations.

Change-Id: I3338f4e68387b2835b2e58d6df65d740d6a648cb
Reviewed-on: https://go-review.googlesource.com/c/go/+/323309
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
Trust: Dan Scales <danscales@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>

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

@@ -46,7 +46,12 @@ func (g *irgen) importDecl(p *noder, decl *syntax.ImportDecl) {
 
 	g.pragmaFlags(decl.Pragma, 0)
 
-	ipkg := importfile(decl)
+	// Get the imported package's path, as resolved already by types2
+	// and gcimporter. This is the same path as would be computed by
+	// parseImportPath.
+	path := pkgNameOf(g.info, decl).Imported().Path()
+
+	ipkg := readImportFile(g.target, path)
 	if ipkg == ir.Pkgs.Unsafe {
 		p.importedUnsafe = true
 	}
@@ -55,6 +60,14 @@ func (g *irgen) importDecl(p *noder, decl *syntax.ImportDecl) {
 	}
 }
 
+// pkgNameOf returns the PkgName associated with the given ImportDecl.
+func pkgNameOf(info *types2.Info, decl *syntax.ImportDecl) *types2.PkgName {
+	if name := decl.LocalPkgName; name != nil {
+		return info.Defs[name].(*types2.PkgName)
+	}
+	return info.Implicits[decl].(*types2.PkgName)
+}
+
 func (g *irgen) constDecl(out *ir.Nodes, decl *syntax.ConstDecl) {
 	g.pragmaFlags(decl.Pragma, 0)
 

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

@@ -175,36 +175,44 @@ func resolveImportPath(path string) (string, error) {
 	return path, nil
 }
 
-// TODO(mdempsky): Return an error instead.
 func importfile(decl *syntax.ImportDecl) *types.Pkg {
-	if decl.Path.Kind != syntax.StringLit {
-		base.Errorf("import path must be a string")
-		return nil
-	}
-
-	path, err := strconv.Unquote(decl.Path.Value)
-	if err != nil {
-		base.Errorf("import path must be a string")
-		return nil
-	}
-
-	if err := checkImportPath(path, false); err != nil {
-		base.Errorf("%s", err.Error())
-		return nil
-	}
-
-	path, err = resolveImportPath(path)
+	path, err := parseImportPath(decl.Path)
 	if err != nil {
 		base.Errorf("%s", err)
 		return nil
 	}
 
+	pkg := readImportFile(typecheck.Target, path)
+	if pkg != ir.Pkgs.Unsafe && pkg.Height >= myheight {
+		myheight = pkg.Height + 1
+	}
+	return pkg
+}
+
+func parseImportPath(pathLit *syntax.BasicLit) (string, error) {
+	if pathLit.Kind != syntax.StringLit {
+		return "", errors.New("import path must be a string")
+	}
+
+	path, err := strconv.Unquote(pathLit.Value)
+	if err != nil {
+		return "", errors.New("import path must be a string")
+	}
+
+	if err := checkImportPath(path, false); err != nil {
+		return "", err
+	}
+
+	return resolveImportPath(path)
+}
+
+func readImportFile(target *ir.Package, path string) *types.Pkg {
 	importpkg := types.NewPkg(path, "")
 	if importpkg.Direct {
 		return importpkg // already fully loaded
 	}
 	importpkg.Direct = true
-	typecheck.Target.Imports = append(typecheck.Target.Imports, importpkg)
+	target.Imports = append(target.Imports, importpkg)
 
 	if path == "unsafe" {
 		return importpkg // initialized with universe
@@ -324,10 +332,6 @@ func importfile(decl *syntax.ImportDecl) *types.Pkg {
 		base.Ctxt.AddImport(file[len(file)-len(path)-len(".a"):], fingerprint)
 	}
 
-	if importpkg.Height >= myheight {
-		myheight = importpkg.Height + 1
-	}
-
 	return importpkg
 }
 

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

@@ -98,6 +98,7 @@ type irgen struct {
 
 func (g *irgen) generate(noders []*noder) {
 	types.LocalPkg.Name = g.self.Name()
+	types.LocalPkg.Height = g.self.Height()
 	typecheck.TypecheckAllowed = true
 
 	// Prevent size calculations until we set the underlying type
@@ -132,8 +133,6 @@ Outer:
 			}
 		}
 	}
-	assert(myheight == g.self.Height())
-	types.LocalPkg.Height = myheight
 
 	// 2. Process all package-block type declarations. As with imports,
 	// we need to make sure all types are properly instantiated before