diagnostics: sort package diagnostics by position

Previously, the error messages could be shown out of order.
With this patch, the errors are sorted before being shown to the user.
This makes it easier to read the error messages, and matches what the
`go` toolchain does.

diagnostics/diagnostics.go

@@ -10,6 +10,7 @@ import (
 	"go/types"
 	"io"
 	"path/filepath"
+	"sort"
 	"strings"
 
 	"github.com/tinygo-org/tinygo/builder"
@@ -59,6 +60,7 @@ func CreateDiagnostics(err error) ProgramDiagnostic {
 // Create diagnostics for a single package (though, in practice, it may also be
 // used for whole-program diagnostics in some cases).
 func createPackageDiagnostic(err error) PackageDiagnostic {
+	// Extract diagnostics for this package.
 	var pkgDiag PackageDiagnostic
 	switch err := err.(type) {
 	case loader.Errors:
@@ -89,7 +91,20 @@ func createPackageDiagnostic(err error) PackageDiagnostic {
 	default:
 		pkgDiag.Diagnostics = createDiagnostics(err)
 	}
-	// TODO: sort
+
+	// Sort these diagnostics by file/line/column.
+	sort.SliceStable(pkgDiag.Diagnostics, func(i, j int) bool {
+		posI := pkgDiag.Diagnostics[i].Pos
+		posJ := pkgDiag.Diagnostics[j].Pos
+		if posI.Filename != posJ.Filename {
+			return posI.Filename < posJ.Filename
+		}
+		if posI.Line != posJ.Line {
+			return posI.Line < posJ.Line
+		}
+		return posI.Column < posJ.Column
+	})
+
 	return pkgDiag
 }
 

testdata/errors/types.go

@@ -7,6 +7,6 @@ func main() {
 }
 
 // ERROR: # command-line-arguments
+// ERROR: types.go:4:6: a declared and not used
 // ERROR: types.go:5:6: cannot use "foobar" (untyped string constant) as int value in assignment
 // ERROR: types.go:6:2: undefined: nonexisting
-// ERROR: types.go:4:6: a declared and not used