cmd/go/testdata/script: make list_case_collision's behavior more clear

Implementing the suggestion made by bcmills on a comment on golang.org/cl/228783.

Change-Id: I314a24a002c65b582ea51610dcc1a54a69afbb8c
Reviewed-on: https://go-review.googlesource.com/c/go/+/229705
Run-TryBot: Michael Matloob <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>

Author: matloob

src/cmd/go/script_test.go

@@ -22,6 +22,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -296,6 +297,8 @@ Script:
 				ok = os.Geteuid() == 0
 			case "symlink":
 				ok = testenv.HasSymlink()
+			case "case-sensitive":
+				ok = isCaseSensitive(ts.t)
 			default:
 				if strings.HasPrefix(cond.tag, "exec:") {
 					prog := cond.tag[len("exec:"):]
@@ -364,6 +367,41 @@ Script:
 	}
 }
 
+var (
+	onceCaseSensitive sync.Once
+	caseSensitive     bool
+)
+
+func isCaseSensitive(t *testing.T) bool {
+	onceCaseSensitive.Do(func() {
+		tmpdir, err := ioutil.TempDir("", "case-sensitive")
+		if err != nil {
+			t.Fatal("failed to create directory to determine case-sensitivity:", err)
+		}
+		defer os.RemoveAll(tmpdir)
+
+		fcap := filepath.Join(tmpdir, "FILE")
+		if err := ioutil.WriteFile(fcap, []byte{}, 0644); err != nil {
+			t.Fatal("error writing file to determine case-sensitivity:", err)
+		}
+
+		flow := filepath.Join(tmpdir, "file")
+		_, err = ioutil.ReadFile(flow)
+		switch {
+		case err == nil:
+			caseSensitive = false
+			return
+		case os.IsNotExist(err):
+			caseSensitive = true
+			return
+		default:
+			t.Fatal("unexpected error reading file when determining case-sensitivity:", err)
+		}
+	})
+
+	return caseSensitive
+}
+
 // scriptCmds are the script command implementations.
 // Keep list and the implementations below sorted by name.
 //

src/cmd/go/testdata/script/README

@@ -85,6 +85,7 @@ should only run when the condition is satisfied. The available conditions are:
    - [link] for testenv.HasLink()
    - [root] for os.Geteuid() == 0
    - [symlink] for testenv.HasSymlink()
+   - [case-sensitive] for whether the file system is case-sensitive
    - [exec:prog] for whether prog is available for execution (found by exec.LookPath)
    - [GODEBUG:value] for whether value is one of the comma-separated entries in the GODEBUG variable
    - [buildmode:value] for whether -buildmode=value is supported

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

@@ -6,23 +6,20 @@ stdout 'case-insensitive import collision'
 ! go build example/a
 stderr 'case-insensitive import collision'
 
-# If we're not guaranteed to have a case-sensitive file system, list files explicitly on command line.
-# Otherwise, let directory read find both files.
-[darwin] ! go list example/b/file.go example/b/FILE.go
-[windows] ! go list example/b/file.go example/b/FILE.go
-[!darwin] [!windows] ! go list example/b
+# List files explicitly on command line, to encounter case-checking
+# logic even on case-insensitive filesystems.
+cp example/b/file.go example/b/FILE.go  # no-op on case-insensitive filesystems
+! go list example/b/file.go example/b/FILE.go
 stderr 'case-insensitive file name collision'
 
+mkdir example/a/Pkg  # no-op on case-insensitive filesystems
+cp example/a/pkg/pkg.go example/a/Pkg/pkg.go  # no-op on case-insensitive filesystems
 ! go list example/a/pkg example/a/Pkg
-stderr 'case-insensitive import collision'
-go list -json -e example/a/pkg example/a/Pkg
-stdout 'case-insensitive import collision'
-! go build example/a/pkg example/a/Pkg
-stderr 'case-insensitive import collision'
 
 # Test that the path reported with an indirect import is correct.
-[!darwin] [!windows] ! go build example/c
-[!darwin] [!windows] stderr '^package example/c\n\timports example/b: case-insensitive file name collision: "FILE.go" and "file.go"$'
+cp example/b/file.go example/b/FILE.go
+[case-sensitive] ! go build example/c
+[case-sensitive] stderr '^package example/c\n\timports example/b: case-insensitive file name collision: "FILE.go" and "file.go"$'
 
 -- example/a/a.go --
 package p
@@ -32,12 +29,8 @@ import (
 )
 -- example/a/pkg/pkg.go --
 package pkg
--- example/a/Pkg/pkg.go --
-package pkg
 -- example/b/file.go --
 package b
--- example/b/FILE.go --
-package b
 -- example/c/c.go --
 package c