cmd/go: honor -fullpath for compiler diagnostics

src/cmd/go/internal/cfg/cfg.go

@@ -81,6 +81,7 @@ var (
 	BuildCover             bool                    // -cover flag
 	BuildCoverMode         string                  // -covermode flag
 	BuildCoverPkg          []string                // -coverpkg flag
+	BuildFullpath          bool                    // -fullpath flag
 	BuildJSON              bool                    // -json flag
 	BuildN                 bool                    // -n flag
 	BuildO                 string                  // -o flag

src/cmd/go/internal/load/pkg.go

@@ -308,7 +308,9 @@ func (p *Package) setLoadPackageDataError(err error, path string, stk *ImportSta
 		isScanErr = true // For stack push/pop below.
 
 		scanPos := scanErr[0].Pos
-		scanPos.Filename = base.ShortPath(scanPos.Filename)
+		if !cfg.BuildFullpath {
+			scanPos.Filename = base.ShortPath(scanPos.Filename)
+		}
 		pos = scanPos.String()
 		err = errors.New(scanErr[0].Msg)
 	}
@@ -507,7 +509,9 @@ func (p *PackageError) setPos(posList []token.Position) {
 		return
 	}
 	pos := posList[0]
-	pos.Filename = base.ShortPath(pos.Filename)
+	if !cfg.BuildFullpath {
+		pos.Filename = base.ShortPath(pos.Filename)
+	}
 	p.Pos = pos.String()
 }
 

src/cmd/go/internal/test/testflag.go

@@ -55,7 +55,6 @@ func init() {
 	cf.StringVar(&testCPUProfile, "cpuprofile", "", "")
 	cf.BoolVar(&testFailFast, "failfast", false, "")
 	cf.StringVar(&testFuzz, "fuzz", "", "")
-	cf.Bool("fullpath", false, "")
 	cf.StringVar(&testList, "list", "", "")
 	cf.StringVar(&testMemProfile, "memprofile", "", "")
 	cf.String("memprofilerate", "", "")

src/cmd/go/internal/work/build.go

@@ -135,6 +135,8 @@ and test commands:
 		arguments to pass on each gccgo compiler/linker invocation.
 	-gcflags '[pattern=]arg list'
 		arguments to pass on each go tool compile invocation.
+	-fullpath
+		show full file names in error messages.
 	-installsuffix suffix
 		a suffix to use in the name of the package installation directory,
 		in order to keep output separate from default builds.
@@ -323,6 +325,7 @@ func AddBuildFlags(cmd *base.Command, mask BuildFlagMask) {
 	cmd.Flag.Var(buildCompiler{}, "compiler", "")
 	cmd.Flag.StringVar(&cfg.BuildBuildmode, "buildmode", "default", "")
 	cmd.Flag.Var((*buildvcsFlag)(&cfg.BuildBuildvcs), "buildvcs", "")
+	cmd.Flag.BoolVar(&cfg.BuildFullpath, "fullpath", false, "")
 	cmd.Flag.Var(&load.BuildGcflags, "gcflags", "")
 	cmd.Flag.Var(&load.BuildGccgoflags, "gccgoflags", "")
 	if mask&OmitModFlag == 0 {

src/cmd/go/internal/work/shell.go

@@ -495,12 +495,14 @@ func (sh *Shell) reportCmd(desc, dir string, cmdOut []byte, cmdErr error) error
 		// prefixes, the only way to find them is to look.
 		// This doesn't always produce a relative path --
 		// /foo is shorter than ../../.., for example.
-		if reldir := base.ShortPath(dir); reldir != dir {
-			out = replacePrefix(out, dir, reldir)
-			if filepath.Separator == '\\' {
-				// Don't know why, sometimes this comes out with slashes, not backslashes.
-				wdir := strings.ReplaceAll(dir, "\\", "/")
-				out = replacePrefix(out, wdir, reldir)
+		if !cfg.BuildFullpath {
+			if reldir := base.ShortPath(dir); reldir != dir {
+				out = replacePrefix(out, dir, reldir)
+				if filepath.Separator == '\\' {
+					// Don't know why, sometimes this comes out with slashes, not backslashes.
+					wdir := strings.ReplaceAll(dir, "\\", "/")
+					out = replacePrefix(out, wdir, reldir)
+				}
 			}
 		}
 		dirP := filepath.Dir(dir)

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

@@ -7,6 +7,11 @@ stdout '^ +.+/gopath/src/x/fullpath/fullpath_test.go:8: test failed'
 ! go test ./x/...
 stdout '^ +fullpath_test.go:8: test failed'
 
+# compiler diagnostics should also use full paths.
+! go test -C ./y -fullpath .
+stderr '^.*'${/}'y'${/}'y.go:3:9: undefined: mistake$'
+! stderr '^\./y.go:3:9: undefined: mistake$'
+
 -- go.mod --
 module example
 -- x/fullpath/fullpath_test.go --
@@ -19,3 +24,7 @@ import (
 func TestFullPath(t *testing.T) {
 	t.Error("test failed")
 }
+-- y/y.go --
+package y
+
+var _ = mistake