separate and rename prefillObjectMaps

The name and docs on that func were wildly out of date,
since it no longer has anything to do with reflection at all.

We only use the linkerVariableStrings map with -literals,
so we can avoid the call entirely if the flag isn't set.

main.go

@@ -922,8 +922,10 @@ func transformCompile(args []string) ([]string, error) {
 
 	// These maps are not kept in pkgCache, since they are only needed to obfuscate curPkg.
 	tf.fieldToStruct = computeFieldToStruct(tf.info)
-	if err := tf.prefillObjectMaps(files); err != nil {
-		return nil, err
+	if flagLiterals {
+		if tf.linkerVariableStrings, err = computeLinkerVariableStrings(tf.pkg, files); err != nil {
+			return nil, err
+		}
 	}
 
 	flags = alterTrimpath(flags)
@@ -1445,12 +1447,11 @@ func loadPkgCache(pkg *types.Package, files []*ast.File, info *types.Info) error
 //go:generate go run golang.org/x/tools/cmd/bundle@v0.5.0 -o cmdgo_quoted.go -prefix cmdgoQuoted cmd/internal/quoted
 //go:generate sed -i /go:generate/d cmdgo_quoted.go
 
-// prefillObjectMaps collects objects which should not be obfuscated,
-// such as those used as arguments to reflect.TypeOf or reflect.ValueOf.
-// Since we obfuscate one package at a time, we only detect those if the type
-// definition and the reflect usage are both in the same package.
-func (tf *transformer) prefillObjectMaps(files []*ast.File) error {
-	tf.linkerVariableStrings = make(map[*types.Var]string)
+// computeLinkerVariableStrings iterates over the -ldflags arguments,
+// filling a map with all the string values set via the linker's -X flag.
+// TODO: can we put this in sharedCache, using objectString as a key?
+func computeLinkerVariableStrings(pkg *types.Package, files []*ast.File) (map[*types.Var]string, error) {
+	linkerVariableStrings := make(map[*types.Var]string)
 
 	// TODO: this is a linker flag that affects how we obfuscate a package at
 	// compile time. Note that, if the user changes ldflags, then Go may only
@@ -1467,7 +1468,7 @@ func (tf *transformer) prefillObjectMaps(files []*ast.File) error {
 	// or to force including -ldflags into the build cache key.
 	ldflags, err := cmdgoQuotedSplit(flagValue(sharedCache.ForwardBuildFlags, "-ldflags"))
 	if err != nil {
-		return err
+		return nil, err
 	}
 	flagValueIter(ldflags, "-X", func(val string) {
 		// val is in the form of "foo.com/bar.name=value".
@@ -1485,13 +1486,13 @@ func (tf *transformer) prefillObjectMaps(files []*ast.File) error {
 			return // not the current package
 		}
 
-		obj, _ := tf.pkg.Scope().Lookup(name).(*types.Var)
+		obj, _ := pkg.Scope().Lookup(name).(*types.Var)
 		if obj == nil {
 			return // no such variable; skip
 		}
-		tf.linkerVariableStrings[obj] = stringValue
+		linkerVariableStrings[obj] = stringValue
 	})
-	return nil
+	return linkerVariableStrings, nil
 }
 
 // transformer holds all the information and state necessary to obfuscate a
@@ -1501,9 +1502,9 @@ type transformer struct {
 	pkg  *types.Package
 	info *types.Info
 
-	// linkerVariableStrings is also initialized by prefillObjectMaps.
-	// It records objects for variables used in -ldflags=-X flags,
+	// linkerVariableStrings records objects for variables used in -ldflags=-X flags,
 	// as well as the strings the user wants to inject them with.
+	// Used when obfuscating literals, so that we obfuscate the injected value.
 	linkerVariableStrings map[*types.Var]string
 
 	// fieldToStruct helps locate struct types from any of their field