Improve Tailwind/PostCSS error messages

Fixes #7041
Fixes #7042

resources/resource_transformers/postcss/postcss_test.go

@@ -14,8 +14,17 @@
 package postcss
 
 import (
+	"regexp"
+	"strings"
 	"testing"
 
+	"github.com/gohugoio/hugo/htesting/hqt"
+
+	"github.com/gohugoio/hugo/common/loggers"
+	"github.com/gohugoio/hugo/helpers"
+
+	"github.com/spf13/afero"
+
 	qt "github.com/frankban/quicktest"
 )
 
@@ -40,6 +49,7 @@ func TestDecodeOptions(t *testing.T) {
 
 func TestShouldImport(t *testing.T) {
 	c := qt.New(t)
+	var imp *importResolver
 
 	for _, test := range []struct {
 		input  string
@@ -52,6 +62,106 @@ func TestShouldImport(t *testing.T) {
 		{input: `@import url("navigation.css");`, expect: false},
 		{input: `@import url('https://fonts.googleapis.com/css?family=Open+Sans:400,400i,800,800i&display=swap');`, expect: false},
 	} {
-		c.Assert(shouldImport(test.input), qt.Equals, test.expect)
+		c.Assert(imp.shouldImport(test.input), qt.Equals, test.expect)
+	}
+}
+
+func TestImportResolver(t *testing.T) {
+	c := qt.New(t)
+	fs := afero.NewMemMapFs()
+
+	writeFile := func(name, content string) {
+		c.Assert(afero.WriteFile(fs, name, []byte(content), 0777), qt.IsNil)
+	}
+
+	writeFile("a.css", `@import "b.css";
+@import "c.css";
+A_STYLE1
+A_STYLE2
+`)
+
+	writeFile("b.css", `B_STYLE`)
+	writeFile("c.css", "@import \"d.css\"\nC_STYLE")
+	writeFile("d.css", "@import \"a.css\"\n\nD_STYLE")
+	writeFile("e.css", "E_STYLE")
+
+	mainStyles := strings.NewReader(`@import "a.css";
+@import "b.css";
+LOCAL_STYLE
+@import "c.css";
+@import "e.css";
+@import "missing.css";`)
+
+	imp := newImportResolver(
+		mainStyles,
+		"styles.css",
+		fs, loggers.NewErrorLogger(),
+	)
+
+	r, err := imp.resolve()
+	c.Assert(err, qt.IsNil)
+	rs := helpers.ReaderToString(r)
+	result := regexp.MustCompile(`\n+`).ReplaceAllString(rs, "\n")
+
+	c.Assert(result, hqt.IsSameString, `B_STYLE
+D_STYLE
+C_STYLE
+A_STYLE1
+A_STYLE2
+LOCAL_STYLE
+E_STYLE
+@import "missing.css";`)
+
+	dline := imp.linemap[3]
+	c.Assert(dline, qt.DeepEquals, fileOffset{
+		Offset:   1,
+		Filename: "d.css",
+	})
+
+}
+
+func BenchmarkImportResolver(b *testing.B) {
+	c := qt.New(b)
+	fs := afero.NewMemMapFs()
+
+	writeFile := func(name, content string) {
+		c.Assert(afero.WriteFile(fs, name, []byte(content), 0777), qt.IsNil)
+	}
+
+	writeFile("a.css", `@import "b.css";
+@import "c.css";
+A_STYLE1
+A_STYLE2
+`)
+
+	writeFile("b.css", `B_STYLE`)
+	writeFile("c.css", "@import \"d.css\"\nC_STYLE"+strings.Repeat("\nSTYLE", 12))
+	writeFile("d.css", "@import \"a.css\"\n\nD_STYLE"+strings.Repeat("\nSTYLE", 55))
+	writeFile("e.css", "E_STYLE")
+
+	mainStyles := `@import "a.css";
+@import "b.css";
+LOCAL_STYLE
+@import "c.css";
+@import "e.css";
+@import "missing.css";`
+
+	logger := loggers.NewErrorLogger()
+
+	for i := 0; i < b.N; i++ {
+		b.StopTimer()
+		imp := newImportResolver(
+			strings.NewReader(mainStyles),
+			"styles.css",
+			fs, logger,
+		)
+
+		b.StartTimer()
+
+		_, err := imp.resolve()
+		if err != nil {
+			b.Fatal(err)
+		}
+
 	}
 }