[dev.typeparams] cmd/compile/internal/types2: report unused packages in source order

1) Rather than map-iterate through all file scopes and collect unused
   packages, collect all imports in the Checker.imports list so that
   errors are reported in source order.

2) From cmd/compile, borrow the idea of a "dotImportRefs" map to map
   dot-imported objects to the package they were dot-imported through
   (we call the map "dotImportMap").

3) From cmd/compile, borrow the "pkgnotused" function
   (called Checker.errorUnusedPkg in this code) and clean up
   unused package error reporting.

4) Adjust unused package error message to match compiler message exactly.

5) Enable one more excluded test case in test/run.go.

Change-Id: I4e4e55512a6043a7fd54f576c7441e3dd4077d6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/287072
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

src/cmd/compile/internal/types2/check.go

@@ -74,6 +74,12 @@ type importKey struct {
 	path, dir string
 }
 
+// A dotImportKey describes a dot-imported object in the given scope.
+type dotImportKey struct {
+	scope *Scope
+	obj   Object
+}
+
 // A Checker maintains the state of the type checker.
 // It must be created with NewChecker.
 type Checker struct {
@@ -92,8 +98,9 @@ type Checker struct {
 	// information collected during type-checking of a set of package files
 	// (initialized by Files, valid only for the duration of check.Files;
 	// maps and lists are allocated on demand)
-	files            []*syntax.File                     // package files
+	files        []*syntax.File            // list of package files
-	unusedDotImports map[*Scope]map[*Package]syntax.Pos // positions of unused dot-imported packages for each file scope
+	imports      []*PkgName                // list of imported packages
+	dotImportMap map[dotImportKey]*PkgName // maps dot-imported objects to the package they were dot-imported through
 
 	firstErr error                    // first error encountered
 	methods  map[*TypeName][]*Func    // maps package scope type names to associated non-blank (non-interface) methods
@@ -110,22 +117,6 @@ type Checker struct {
 	indent int // indentation for tracing
 }
 
-// addUnusedImport adds the position of a dot-imported package
-// pkg to the map of dot imports for the given file scope.
-func (check *Checker) addUnusedDotImport(scope *Scope, pkg *Package, pos syntax.Pos) {
-	mm := check.unusedDotImports
-	if mm == nil {
-		mm = make(map[*Scope]map[*Package]syntax.Pos)
-		check.unusedDotImports = mm
-	}
-	m := mm[scope]
-	if m == nil {
-		m = make(map[*Package]syntax.Pos)
-		mm[scope] = m
-	}
-	m[pkg] = pos
-}
-
 // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
 func (check *Checker) addDeclDep(to Object) {
 	from := check.decl
@@ -209,7 +200,8 @@ func NewChecker(conf *Config, pkg *Package, info *Info) *Checker {
 func (check *Checker) initFiles(files []*syntax.File) {
 	// start with a clean slate (check.Files may be called multiple times)
 	check.files = nil
-	check.unusedDotImports = nil
+	check.imports = nil
+	check.dotImportMap = nil
 
 	check.firstErr = nil
 	check.methods = nil
@@ -291,6 +283,9 @@ func (check *Checker) checkFiles(files []*syntax.File) (err error) {
 		print("== unusedImports ==")
 		check.unusedImports()
 	}
+	// no longer needed - release memory
+	check.imports = nil
+	check.dotImportMap = nil
 
 	print("== recordUntyped ==")
 	check.recordUntyped()
@@ -301,6 +296,9 @@ func (check *Checker) checkFiles(files []*syntax.File) (err error) {
 	}
 
 	check.pkg.complete = true
+
+	// TODO(gri) There's more memory we should release at this point.
+
 	return
 }
 

src/cmd/compile/internal/types2/resolver.go

@@ -273,21 +273,26 @@ func (check *Checker) collectObjects() {
 					}
 				}
 
-				obj := NewPkgName(s.Pos(), pkg, name, imp)
+				pkgName := NewPkgName(s.Pos(), pkg, name, imp)
 				if s.LocalPkgName != nil {
 					// in a dot-import, the dot represents the package
-					check.recordDef(s.LocalPkgName, obj)
+					check.recordDef(s.LocalPkgName, pkgName)
 				} else {
-					check.recordImplicit(s, obj)
+					check.recordImplicit(s, pkgName)
 				}
 
 				if path == "C" {
 					// match cmd/compile (not prescribed by spec)
-					obj.used = true
+					pkgName.used = true
 				}
 
 				// add import to file scope
+				check.imports = append(check.imports, pkgName)
 				if name == "." {
+					// dot-import
+					if check.dotImportMap == nil {
+						check.dotImportMap = make(map[dotImportKey]*PkgName)
+					}
 					// merge imported scope with file scope
 					for _, obj := range imp.scope.elems {
 						// A package scope may contain non-exported objects,
@@ -301,16 +306,15 @@ func (check *Checker) collectObjects() {
 							if alt := fileScope.Insert(obj); alt != nil {
 								check.errorf(s.LocalPkgName, "%s redeclared in this block", obj.Name())
 								check.reportAltDecl(alt)
+							} else {
+								check.dotImportMap[dotImportKey{fileScope, obj}] = pkgName
 							}
 						}
 					}
-					// add position to set of dot-import positions for this file
-					// (this is only needed for "imported but not used" errors)
-					check.addUnusedDotImport(fileScope, imp, s.Pos())
 				} else {
 					// declare imported package object in file scope
 					// (no need to provide s.LocalPkgName since we called check.recordDef earlier)
-					check.declare(fileScope, nil, obj, nopos)
+					check.declare(fileScope, nil, pkgName, nopos)
 				}
 
 			case *syntax.ConstDecl:
@@ -673,52 +677,39 @@ func (check *Checker) unusedImports() {
 	// any of its exported identifiers. To import a package solely for its side-effects
 	// (initialization), use the blank identifier as explicit package name."
 
-	// check use of regular imported packages
+	for _, obj := range check.imports {
-	for _, scope := range check.pkg.scope.children /* file scopes */ {
+		if !obj.used && obj.name != "_" {
-		for _, obj := range scope.elems {
+			check.errorUnusedPkg(obj)
-			if obj, ok := obj.(*PkgName); ok {
+		}
-				// Unused "blank imports" are automatically ignored
+	}
-				// since _ identifiers are not entered into scopes.
+}
-				if !obj.used {
+
+func (check *Checker) errorUnusedPkg(obj *PkgName) {
+	// If the package was imported with a name other than the final
+	// import path element, show it explicitly in the error message.
+	// Note that this handles both renamed imports and imports of
+	// packages containing unconventional package declarations.
+	// Note that this uses / always, even on Windows, because Go import
+	// paths always use forward slashes.
 	path := obj.imported.path
-					base := pkgName(path)
+	elem := path
-					if obj.name == base {
+	if i := strings.LastIndex(elem, "/"); i >= 0 {
+		elem = elem[i+1:]
+	}
+	if obj.name == "" || obj.name == "." || obj.name == elem {
 		if check.conf.CompilerErrorMessages {
-							check.softErrorf(obj.pos, "%q imported and not used", path)
+			check.softErrorf(obj, "imported and not used: %q", path)
 		} else {
-							check.softErrorf(obj.pos, "%q imported but not used", path)
+			check.softErrorf(obj, "%q imported but not used", path)
 		}
 	} else {
 		if check.conf.CompilerErrorMessages {
-							check.softErrorf(obj.pos, "%q imported and not used as %s", path, obj.name)
+			check.softErrorf(obj, "imported and not used: %q as %s", path, obj.name)
 		} else {
-							check.softErrorf(obj.pos, "%q imported but not used as %s", path, obj.name)
+			check.softErrorf(obj, "%q imported but not used as %s", path, obj.name)
 		}
 	}
 }
-			}
-		}
-	}
-
-	// check use of dot-imported packages
-	for _, unusedDotImports := range check.unusedDotImports {
-		for pkg, pos := range unusedDotImports {
-			if check.conf.CompilerErrorMessages {
-				check.softErrorf(pos, "%q imported and not used", pkg.path)
-			} else {
-				check.softErrorf(pos, "%q imported but not used", pkg.path)
-			}
-		}
-	}
-}
-
-// pkgName returns the package name (last element) of an import path.
-func pkgName(path string) string {
-	if i := strings.LastIndex(path, "/"); i >= 0 {
-		path = path[i+1:]
-	}
-	return path
-}
 
 // dir makes a good-faith attempt to return the directory
 // portion of path. If path is empty, the result is ".".

src/cmd/compile/internal/types2/testdata/importdecl0/importdecl0b.src

@@ -8,7 +8,7 @@ import "math"
 import m "math"
 
 import . "testing" // declares T in file scope
-import . /* ERROR "imported but not used" */ "unsafe"
+import . /* ERROR .unsafe. imported but not used */ "unsafe"
 import . "fmt"     // declares Println in file scope
 
 import (

src/cmd/compile/internal/types2/testdata/importdecl1/importdecl1b.src

@@ -4,7 +4,7 @@
 
 package importdecl1
 
-import . /* ERROR "imported but not used" */ "unsafe"
+import . /* ERROR .unsafe. imported but not used */ "unsafe"
 
 type B interface {
 	A

src/cmd/compile/internal/types2/typexpr.go

@@ -56,12 +56,12 @@ func (check *Checker) ident(x *operand, e *syntax.Name, def *Named, wantType boo
 	}
 	assert(typ != nil)
 
-	// The object may be dot-imported: If so, remove its package from
+	// The object may have been dot-imported.
-	// the map of unused dot imports for the respective file scope.
+	// If so, mark the respective package as used.
 	// (This code is only needed for dot-imports. Without them,
 	// we only have to mark variables, see *Var case below).
-	if pkg := obj.Pkg(); pkg != check.pkg && pkg != nil {
+	if pkgName := check.dotImportMap[dotImportKey{scope, obj}]; pkgName != nil {
-		delete(check.unusedDotImports[scope], pkg)
+		pkgName.used = true
 	}
 
 	switch obj := obj.(type) {

test/run.go

@@ -1956,7 +1956,6 @@ var excluded = map[string]bool{
 	"fixedbugs/issue18331.go":  true, // missing error about misuse of //go:noescape (irgen needs code from noder)
 	"fixedbugs/issue18393.go":  true, // types2 not run after syntax errors
 	"fixedbugs/issue19012.go":  true, // multiple errors on same line
-	"fixedbugs/issue20298.go":  true, // types2 non-deterministically reports unused imports
 	"fixedbugs/issue20233.go":  true, // types2 reports two instead of one error (pref: compiler)
 	"fixedbugs/issue20245.go":  true, // types2 reports two instead of one error (pref: compiler)
 	"fixedbugs/issue20250.go":  true, // correct diagnostics, but different lines (probably irgen's fault)