go/packages: opt: ignore function bodies in non-initial packages

This saves 35% of wall time in a command such as

 $ gopackages -mode=syntax golang.org/x/tools/go/packages/gopackages fmt

that would otherwise typecheck every function in each package that
depends on fmt. It also applies in -mode=types when source was loaded
as a fall back for missing export data due to an error in a lower package.

Also, remove Config.TypeChecker field now that not a single of its
subfields is passed through go/packages to the type checker.
(The Sizes function is logically a result, not an input, of loading,
though we have yet to implement it properly.)

Change-Id: I472d21b34fc5e2832f7353e82992a67a06e4e4cc
Reviewed-on: https://go-review.googlesource.com/129497
Reviewed-by: Ian Cottrell <iancottrell@google.com>

cmd/ssadump/main.go

@@ -86,7 +86,7 @@ func doMain() error {
 	case "386", "arm":
 		wordSize = 4
 	}
-	cfg.TypeChecker.Sizes = &types.StdSizes{
+	sizes := &types.StdSizes{
 		MaxAlign: 8,
 		WordSize: wordSize,
 	}
@@ -164,7 +164,7 @@ func doMain() error {
 		// Run first main package.
 		for _, main := range ssautil.MainPackages(pkgs) {
 			fmt.Fprintf(os.Stderr, "Running: %s\n", main.Pkg.Path())
-			os.Exit(interp.Interpret(main, interpMode, cfg.TypeChecker.Sizes, main.Pkg.Path(), args))
+			os.Exit(interp.Interpret(main, interpMode, sizes, main.Pkg.Path(), args))
 		}
 		return fmt.Errorf("no main package")
 	}

go/packages/packages.go

@@ -124,22 +124,6 @@ type Config struct {
 	// In build systems with explicit names for tests,
 	// setting Tests may have no effect.
 	Tests bool
-
-	// TypeChecker provides additional configuration for type-checking syntax trees.
-	//
-	// It is used for all packages in LoadAllSyntax mode,
-	// and for the packages matching the patterns, but not their dependencies,
-	// in LoadSyntax mode.
-	//
-	// The TypeChecker.Error function is ignored:
-	// errors are reported using the Error function defined above.
-	//
-	// The TypeChecker.Importer function is ignored:
-	// the loader defines an appropriate importer.
-	//
-	// TODO(rsc): TypeChecker.Sizes should use the same sizes as the main build.
-	// Derive them from the runtime?
-	TypeChecker types.Config
 }
 
 // driver is the type for functions that query the build system for the
@@ -364,7 +348,8 @@ type loaderPackage struct {
 	importErrors map[string]error // maps each bad import to its error
 	loadOnce     sync.Once
 	color        uint8 // for cycle detection
-	mark, needsrc bool  // used when Mode >= LoadTypes
+	needsrc      bool  // load from source (Mode >= LoadTypes)
+	initial      bool  // package was matched by a pattern
 }
 
 // loader holds the working state of a single call to load.
@@ -435,6 +420,7 @@ func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
 		ld.pkgs[lpkg.ID] = lpkg
 		if isRoot[lpkg.ID] {
 			initial = append(initial, lpkg)
+			lpkg.initial = true
 		}
 	}
 
@@ -604,9 +590,7 @@ func (ld *loader) loadPackage(lpkg *loaderPackage) {
 		Selections: make(map[*ast.SelectorExpr]*types.Selection),
 	}
 
-	// Copy the prototype types.Config as it must vary across Packages.
+	importer := importerFunc(func(path string) (*types.Package, error) {
-	tc := ld.TypeChecker // copy
-	tc.Importer = importerFunc(func(path string) (*types.Package, error) {
 		if path == "unsafe" {
 			return types.Unsafe, nil
 		}
@@ -630,10 +614,22 @@ func (ld *loader) loadPackage(lpkg *loaderPackage) {
 		log.Fatalf("internal error: nil Pkg importing %q from %q", path, lpkg)
 		panic("unreachable")
 	})
-	tc.Error = appendError
 
 	// type-check
-	types.NewChecker(&tc, ld.Fset, lpkg.Types, lpkg.TypesInfo).Files(lpkg.Syntax)
+	tc := &types.Config{
+		Importer: importer,
+
+		// Type-check bodies of functions only in non-initial packages.
+		// Example: for import graph A->B->C and initial packages {A,C},
+		// we can ignore function bodies in B.
+		IgnoreFuncBodies: ld.Mode < LoadAllSyntax && !lpkg.initial,
+
+		Error: appendError,
+
+		// TODO(adonovan): derive Sizes from the underlying
+		// build system.
+	}
+	types.NewChecker(tc, ld.Fset, lpkg.Types, lpkg.TypesInfo).Files(lpkg.Syntax)
 
 	lpkg.importErrors = nil // no longer needed