cmd/go: don't include package dir in cache key when -trimpath is set

The '-trimpath' flag tells 'go build' to trim any paths from the
output files that are tied to the current workspace or toolchain. When
this flag is set, we do not need to include the package directory in
the text hashed to construct the action ID for each package.

Fixes #33772

Change-Id: I20b902d2f58019709b15864ca79aa0d9255ae707
Reviewed-on: https://go-review.googlesource.com/c/go/+/195318
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/work/exec.go

@@ -201,12 +201,12 @@ func (b *Builder) buildActionID(a *Action) cache.ActionID {
 	// same compiler settings and can reuse each other's results.
 	// If not, the reason is already recorded in buildGcflags.
 	fmt.Fprintf(h, "compile\n")
+	// Only include the package directory if it may affect the output.
+	// We trim workspace paths for all packages when -trimpath is set.
 	// The compiler hides the exact value of $GOROOT
-	// when building things in GOROOT,
-	// but it does not hide the exact value of $GOPATH.
-	// Include the full dir in that case.
+	// when building things in GOROOT.
 	// Assume b.WorkDir is being trimmed properly.
-	if !p.Goroot && !strings.HasPrefix(p.Dir, b.WorkDir) {
+	if !p.Goroot && !cfg.BuildTrimpath && !strings.HasPrefix(p.Dir, b.WorkDir) {
 		fmt.Fprintf(h, "dir %s\n", p.Dir)
 	}
 	fmt.Fprintf(h, "goos %s goarch %s\n", cfg.Goos, cfg.Goarch)

src/cmd/go/script_test.go

@@ -441,10 +441,15 @@ func (ts *testScript) cmdCmp(neg bool, args []string) {
 		// It would be strange to say "this file can have any content except this precise byte sequence".
 		ts.fatalf("unsupported: ! cmp")
 	}
+	quiet := false
+	if len(args) > 0 && args[0] == "-q" {
+		quiet = true
+		args = args[1:]
+	}
 	if len(args) != 2 {
 		ts.fatalf("usage: cmp file1 file2")
 	}
-	ts.doCmdCmp(args, false)
+	ts.doCmdCmp(args, false, quiet)
 }
 
 // cmpenv compares two files with environment variable substitution.
@@ -452,13 +457,18 @@ func (ts *testScript) cmdCmpenv(neg bool, args []string) {
 	if neg {
 		ts.fatalf("unsupported: ! cmpenv")
 	}
+	quiet := false
+	if len(args) > 0 && args[0] == "-q" {
+		quiet = true
+		args = args[1:]
+	}
 	if len(args) != 2 {
 		ts.fatalf("usage: cmpenv file1 file2")
 	}
-	ts.doCmdCmp(args, true)
+	ts.doCmdCmp(args, true, quiet)
 }
 
-func (ts *testScript) doCmdCmp(args []string, env bool) {
+func (ts *testScript) doCmdCmp(args []string, env, quiet bool) {
 	name1, name2 := args[0], args[1]
 	var text1, text2 string
 	if name1 == "stdout" {
@@ -484,7 +494,9 @@ func (ts *testScript) doCmdCmp(args []string, env bool) {
 		return
 	}
 
+	if !quiet {
 		fmt.Fprintf(&ts.log, "[diff -%s +%s]\n%s\n", name1, name2, diff(text1, text2))
+	}
 	ts.fatalf("%s and %s differ", name1, name2)
 }
 

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

@@ -1,21 +1,44 @@
 [short] skip
 
 env -r GOROOT_REGEXP=$GOROOT
-env -r WORK_REGEXP=$WORK
+env -r WORK_REGEXP='$WORK'  # don't expand $WORK; grep replaces $WORK in text before matching.
 env GOROOT GOROOT_REGEXP WORK WORK_REGEXP
 
+# A binary built without -trimpath should contain the current workspace
+# and GOROOT for debugging and stack traces.
+cd a
+go build -o hello.exe hello.go
+grep -q $WORK_REGEXP hello.exe
+grep -q $GOROOT_REGEXP hello.exe
+
+# A binary built with -trimpath should not contain the current workspace
+# or GOROOT.
 go build -trimpath -o hello.exe hello.go
 ! grep -q $GOROOT_REGEXP hello.exe
 ! grep -q $WORK_REGEXP hello.exe
+cd ..
 
+# A binary from an external module built with -trimpath should not contain
+# the current workspace or GOROOT.
 env GO111MODULE=on
 go build -trimpath -o fortune.exe rsc.io/fortune
 ! grep -q $GOROOT_REGEXP fortune.exe
 ! grep -q $WORK_REGEXP fortune.exe
 
--- hello.go --
+# Two binaries built from identical packages in different directories
+# should be identical.
+mkdir b
+cp a/go.mod a/hello.go b
+cd a
+go build -trimpath -o ../a.exe .
+cd ../b
+go build -trimpath -o ../b.exe .
+cd ..
+cmp -q a.exe b.exe
+
+-- a/hello.go --
 package main
 func main() { println("hello") }
 
--- go.mod --
+-- a/go.mod --
 module m