imports: make ScanDir ignore go files start with dot

Adding "." Prefix Check for go files.

Fixes #42047
Change-Id: Ifc42bf562f52fdd304f9828b06fc57888fcd8049
Reviewed-on: https://go-review.googlesource.com/c/go/+/264078
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Trust: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/imports/scan.go

@@ -34,7 +34,7 @@ func ScanDir(dir string, tags map[string]bool) ([]string, []string, error) {
 			}
 		}
 
-		if info.Mode().IsRegular() && !strings.HasPrefix(name, "_") && strings.HasSuffix(name, ".go") && MatchFile(name, tags) {
+		if info.Mode().IsRegular() && !strings.HasPrefix(name, "_") && !strings.HasPrefix(name, ".") && strings.HasSuffix(name, ".go") && MatchFile(name, tags) {
 			files = append(files, filepath.Join(dir, name))
 		}
 	}

src/cmd/go/internal/imports/testdata/android/.h.go

@@ -0,0 +1,3 @@
+package android
+
+import _ "h"

src/cmd/go/internal/imports/testdata/illumos/.h.go

@@ -0,0 +1,3 @@
+package android
+
+import _ "h"

src/cmd/go/testdata/script/import_ignore.txt

@@ -0,0 +1,11 @@
+cp go.mod go.mod.orig
+go mod tidy
+cmp go.mod go.mod.orig
+
+-- go.mod --
+module m.test
+
+go 1.16
+-- .ignore.go --
+package p
+import _ "golang.org/x/mod/modfile"