caddyfile: Use full, absolute file path in token structs (fixes #1892)

When two Caddyfiles with the same name, but different paths, are
imported, it can cause a weird bug because isNewLine() returned false
when it should return true, since the files are actually different,
but it couldn't know that because only the base name was stored,
not the whole path.

caddyfile/parse.go

@@ -212,7 +212,7 @@ func (p *parser) doImport() error {
 	// and then use glob to get list of matching filenames
 	absFile, err := filepath.Abs(p.Dispenser.filename)
 	if err != nil {
-		return p.Errf("Failed to get absolute path of file: %s", p.Dispenser.filename)
+		return p.Errf("Failed to get absolute path of file: %s: %v", p.Dispenser.filename, err)
 	}
 
 	var matches []string
@@ -246,8 +246,8 @@ func (p *parser) doImport() error {
 		if err != nil {
 			return err
 		}
+
 		var importLine int
-		importDir := filepath.Dir(importFile)
 		for i, token := range newTokens {
 			if token.Text == "import" {
 				importLine = token.Line
@@ -260,7 +260,7 @@ func (p *parser) doImport() error {
 				} else if !filepath.IsAbs(importFile) {
 					abs = filepath.Join(filepath.Dir(absFile), token.Text)
 				} else {
-					abs = filepath.Join(importDir, token.Text)
+					abs = filepath.Join(filepath.Dir(importFile), token.Text)
 				}
 				newTokens[i] = Token{
 					Text: abs,
@@ -269,6 +269,7 @@ func (p *parser) doImport() error {
 				}
 			}
 		}
+
 		importedTokens = append(importedTokens, newTokens...)
 	}
 
@@ -300,8 +301,12 @@ func (p *parser) doSingleImport(importFile string) ([]Token, error) {
 		return nil, p.Errf("Could not read tokens while importing %s: %v", importFile, err)
 	}
 
-	// Tack the filename onto these tokens so errors show the imported file's name
-	filename := filepath.Base(importFile)
+	// Tack the file path onto these tokens so errors show the imported file's name
+	// (we use full, absolute path to avoid bugs: issue #1892)
+	filename, err := filepath.Abs(importFile)
+	if err != nil {
+		return nil, p.Errf("Failed to get absolute path of file: %s: %v", p.Dispenser.filename, err)
+	}
 	for i := 0; i < len(importedTokens); i++ {
 		importedTokens[i].File = filename
 	}