1 files changed, 124 insertions, 0 deletions
diff --git a/internal/chunkedfile/chunkedfile.go b/internal/chunkedfile/chunkedfile.go
new file mode 100644
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+++ b/internal/chunkedfile/chunkedfile.go
@@ -0,0 +1,124 @@
+// Copyright 2017 The Bazel Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package chunkedfile provides utilities for testing that source code
+// errors are reported in the appropriate places.
+//
+// A chunked file consists of several chunks of input text separated by
+// "---" lines.  Each chunk is an input to the program under test, such
+// as an evaluator.  Lines containing "###" are interpreted as
+// expectations of failure: the following text is a Go string literal
+// denoting a regular expression that should match the failure message.
+//
+// Example:
+//
+//      x = 1 / 0 ### "division by zero"
+//      ---
+//      x = 1
+//      print(x + "") ### "int + string not supported"
+//
+// A client test feeds each chunk of text into the program under test,
+// then calls chunk.GotError for each error that actually occurred.  Any
+// discrepancy between the actual and expected errors is reported using
+// the client's reporter, which is typically a testing.T.
+package chunkedfile // import "go.starlark.net/internal/chunkedfile"
+
+import (
+	"fmt"
+	"io/ioutil"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+const debug = false
+
+// A Chunk is a portion of a source file.
+// It contains a set of expected errors.
+type Chunk struct {
+	Source   string
+	filename string
+	report   Reporter
+	wantErrs map[int]*regexp.Regexp
+}
+
+// Reporter is implemented by *testing.T.
+type Reporter interface {
+	Errorf(format string, args ...interface{})
+}
+
+// Read parses a chunked file and returns its chunks.
+// It reports failures using the reporter.
+//
+// Error messages of the form "file.star:line:col: ..." are prefixed
+// by a newline so that the Go source position added by (*testing.T).Errorf
+// appears on a separate line so as not to confused editors.
+func Read(filename string, report Reporter) (chunks []Chunk) {
+	data, err := ioutil.ReadFile(filename)
+	if err != nil {
+		report.Errorf("%s", err)
+		return
+	}
+	linenum := 1
+	for i, chunk := range strings.Split(string(data), "\n---\n") {
+		if debug {
+			fmt.Printf("chunk %d at line %d: %s\n", i, linenum, chunk)
+		}
+		// Pad with newlines so the line numbers match the original file.
+		src := strings.Repeat("\n", linenum-1) + chunk
+
+		wantErrs := make(map[int]*regexp.Regexp)
+
+		// Parse comments of the form:
+		// ### "expected error".
+		lines := strings.Split(chunk, "\n")
+		for j := 0; j < len(lines); j, linenum = j+1, linenum+1 {
+			line := lines[j]
+			hashes := strings.Index(line, "###")
+			if hashes < 0 {
+				continue
+			}
+			rest := strings.TrimSpace(line[hashes+len("###"):])
+			pattern, err := strconv.Unquote(rest)
+			if err != nil {
+				report.Errorf("\n%s:%d: not a quoted regexp: %s", filename, linenum, rest)
+				continue
+			}
+			rx, err := regexp.Compile(pattern)
+			if err != nil {
+				report.Errorf("\n%s:%d: %v", filename, linenum, err)
+				continue
+			}
+			wantErrs[linenum] = rx
+			if debug {
+				fmt.Printf("\t%d\t%s\n", linenum, rx)
+			}
+		}
+		linenum++
+
+		chunks = append(chunks, Chunk{src, filename, report, wantErrs})
+	}
+	return chunks
+}
+
+// GotError should be called by the client to report an error at a particular line.
+// GotError reports unexpected errors to the chunk's reporter.
+func (chunk *Chunk) GotError(linenum int, msg string) {
+	if rx, ok := chunk.wantErrs[linenum]; ok {
+		delete(chunk.wantErrs, linenum)
+		if !rx.MatchString(msg) {
+			chunk.report.Errorf("\n%s:%d: error %q does not match pattern %q", chunk.filename, linenum, msg, rx)
+		}
+	} else {
+		chunk.report.Errorf("\n%s:%d: unexpected error: %v", chunk.filename, linenum, msg)
+	}
+}
+
+// Done should be called by the client to indicate that the chunk has no more errors.
+// Done reports expected errors that did not occur to the chunk's reporter.
+func (chunk *Chunk) Done() {
+	for linenum, rx := range chunk.wantErrs {
+		chunk.report.Errorf("\n%s:%d: expected error matching %q", chunk.filename, linenum, rx)
+	}
+}