cmd/go: report position info in package errors

Also refactor common position filling code into a function.

Fixes #18011

Change-Id: I76528626da67a7309193fa92af1e361c8e2fcf84
Reviewed-on: https://go-review.googlesource.com/33631
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -1063,14 +1063,14 @@ func TestInternalPackagesInGOROOTAreRespected(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.runFail("build", "-v", "./testdata/testinternal")
-	tg.grepBoth("use of internal package not allowed", "wrong error message for testdata/testinternal")
+	tg.grepBoth(`testinternal(\/|\\)p\.go\:3\:8\: use of internal package not allowed`, "wrong error message for testdata/testinternal")
 }
 
 func TestInternalPackagesOutsideGOROOTAreRespected(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()
 	tg.runFail("build", "-v", "./testdata/testinternal2")
-	tg.grepBoth("use of internal package not allowed", "wrote error message for testdata/testinternal2")
+	tg.grepBoth(`testinternal2(\/|\\)p\.go\:3\:8\: use of internal package not allowed`, "wrote error message for testdata/testinternal2")
 }
 
 func TestRunInternal(t *testing.T) {
@@ -1080,7 +1080,7 @@ func TestRunInternal(t *testing.T) {
 	tg.setenv("GOPATH", dir)
 	tg.run("run", filepath.Join(dir, "src/run/good.go"))
 	tg.runFail("run", filepath.Join(dir, "src/run/bad.go"))
-	tg.grepStderr("use of internal package not allowed", "unexpected error for run/bad.go")
+	tg.grepStderr(`testdata(\/|\\)src(\/|\\)run(\/|\\)bad\.go\:3\:8\: use of internal package not allowed`, "unexpected error for run/bad.go")
 }
 
 func testMove(t *testing.T, vcs, url, base, config string) {

src/cmd/go/pkg.go

@@ -371,10 +371,8 @@ func loadImport(path, srcDir string, parent *Package, stk *importStack, importPo
 			err = fmt.Errorf("code in directory %s expects import %q", bp.Dir, bp.ImportComment)
 		}
 		p.load(stk, bp, err)
-		if p.Error != nil && p.Error.Pos == "" && len(importPos) > 0 {
-			pos := importPos[0]
-			pos.Filename = shortPath(pos.Filename)
-			p.Error.Pos = pos.String()
+		if p.Error != nil && p.Error.Pos == "" {
+			p = setErrorPos(p, importPos)
 		}
 
 		if origPath != cleanImport(origPath) {
@@ -388,11 +386,11 @@ func loadImport(path, srcDir string, parent *Package, stk *importStack, importPo
 
 	// Checked on every import because the rules depend on the code doing the importing.
 	if perr := disallowInternal(srcDir, p, stk); perr != p {
-		return perr
+		return setErrorPos(perr, importPos)
 	}
 	if mode&useVendor != 0 {
 		if perr := disallowVendor(srcDir, origPath, p, stk); perr != p {
-			return perr
+			return setErrorPos(perr, importPos)
 		}
 	}
 
@@ -402,12 +400,7 @@ func loadImport(path, srcDir string, parent *Package, stk *importStack, importPo
 			ImportStack: stk.copy(),
 			Err:         fmt.Sprintf("import %q is a program, not an importable package", path),
 		}
-		if len(importPos) > 0 {
-			pos := importPos[0]
-			pos.Filename = shortPath(pos.Filename)
-			perr.Error.Pos = pos.String()
-		}
-		return &perr
+		return setErrorPos(&perr, importPos)
 	}
 
 	if p.local && parent != nil && !parent.local {
@@ -416,17 +409,21 @@ func loadImport(path, srcDir string, parent *Package, stk *importStack, importPo
 			ImportStack: stk.copy(),
 			Err:         fmt.Sprintf("local import %q in non-local package", path),
 		}
-		if len(importPos) > 0 {
-			pos := importPos[0]
-			pos.Filename = shortPath(pos.Filename)
-			perr.Error.Pos = pos.String()
-		}
-		return &perr
+		return setErrorPos(&perr, importPos)
 	}
 
 	return p
 }
 
+func setErrorPos(p *Package, importPos []token.Position) *Package {
+	if len(importPos) > 0 {
+		pos := importPos[0]
+		pos.Filename = shortPath(pos.Filename)
+		p.Error.Pos = pos.String()
+	}
+	return p
+}
+
 func cleanImport(path string) string {
 	orig := path
 	path = pathpkg.Clean(path)