add parse error context

cli/queryflags/flags.go

@@ -14,6 +14,7 @@ import (
 	"github.com/brimdata/zed/compiler"
 	"github.com/brimdata/zed/compiler/ast"
 	"github.com/brimdata/zed/compiler/data"
+	"github.com/brimdata/zed/compiler/parser"
 	"github.com/brimdata/zed/compiler/semantic"
 	"github.com/brimdata/zed/pkg/storage"
 	"github.com/brimdata/zed/zbuf"
@@ -40,7 +41,8 @@ func (f *Flags) ParseSourcesAndInputs(paths []string) ([]string, ast.Seq, bool,
 			// Consider a lone argument to be a query if it compiles
 			// and appears to start with a from or yield operator.
 			// Otherwise, consider it a file.
-			if query, err := compiler.Parse(src, f.Includes...); err == nil {
+			query, err := compiler.Parse(src, f.Includes...)
+			if err == nil {
 				if s, err := semantic.Analyze(context.Background(), query, data.NewSource(storage.NewLocalEngine(), nil), nil); err == nil {
 					if semantic.HasSource(s) {
 						return nil, query, false, nil
@@ -50,7 +52,7 @@ func (f *Flags) ParseSourcesAndInputs(paths []string) ([]string, ast.Seq, bool,
 					}
 				}
 			}
-			return nil, nil, false, singleArgError(src)
+			return nil, nil, false, singleArgError(src, err)
 		}
 	}
 	query, err := compiler.Parse(src, f.Includes...)
@@ -78,13 +80,25 @@ func (f *Flags) PrintStats(stats zbuf.Progress) {
 	}
 }
 
-func singleArgError(src string) error {
+func singleArgError(src string, err error) error {
 	var b strings.Builder
 	b.WriteString("could not invoke zq with a single argument because:")
-	b.WriteString("\n - the argument did not parse as a valid Zed query")
 	if len(src) > 20 {
 		src = src[:20] + "..."
 	}
 	fmt.Fprintf(&b, "\n - a file could not be found with the name %q", src)
+	var perr *parser.Error
+	if errors.As(err, &perr) {
+		b.WriteString("\n - the argument could not be compiled as a valid Zed query due to parse error (")
+		if perr.LineNum > 0 {
+			fmt.Fprintf(&b, "line %d, ", perr.LineNum)
+		}
+		fmt.Fprintf(&b, "column %d):", perr.Column)
+		for _, l := range strings.Split(perr.ParseErrorContext(), "\n") {
+			fmt.Fprintf(&b, "\n   %s", l)
+		}
+	} else {
+		b.WriteString("\n - the argument did not parse as a valid Zed query")
+	}
 	return errors.New(b.String())
 }

cmd/zq/ztests/from-pool-error.yaml

@@ -5,5 +5,5 @@ outputs:
   - name: stderr
     data: |
       zq: could not invoke zq with a single argument because:
-       - the argument did not parse as a valid Zed query
        - a file could not be found with the name "from ( pool a )"
+       - the argument did not parse as a valid Zed query

cmd/zq/ztests/no-files.yaml

@@ -7,5 +7,5 @@ outputs:
   - name: stderr
     data: |
       zq: could not invoke zq with a single argument because:
-       - the argument did not parse as a valid Zed query
        - a file could not be found with the name "doesnotexist"
+       - the argument did not parse as a valid Zed query

cmd/zq/ztests/single-arg-error.yaml

@@ -5,5 +5,7 @@ outputs:
   - name: stderr
     data: |
       zq: could not invoke zq with a single argument because:
-       - the argument did not parse as a valid Zed query
        - a file could not be found with the name "file sample.zson | c..."
+       - the argument could not be compiled as a valid Zed query due to parse error (column 25):
+         file sample.zson | count(
+                              === ^ ===

compiler/parser/api.go

@@ -72,10 +72,10 @@ type Error struct {
 	Offset int // offset into original source code
 
 	filename string // omitted from formatting if ""
-	lineNum  int    // zero-based; omitted from formatting if negative
+	LineNum  int    // zero-based; omitted from formatting if negative
 
 	line   string // contains no newlines
-	column int    // zero-based
+	Column int    // zero-based
 }
 
 // NewError returns an Error.  src is the source code containing the error.  If
@@ -105,10 +105,10 @@ func NewError(src string, sis []SourceInfo, offset int) error {
 	}
 	return &Error{
 		Offset:   offset,
+		LineNum:  lineNum,
+		Column:   column,
 		filename: filename,
-		lineNum:  lineNum,
 		line:     src,
-		column:   column,
 	}
 }
 
@@ -119,12 +119,19 @@ func (e *Error) Error() string {
 		fmt.Fprintf(&b, "in %s ", e.filename)
 	}
 	b.WriteString("at ")
-	if e.lineNum >= 0 {
-		fmt.Fprintf(&b, "line %d, ", e.lineNum+1)
+	if e.LineNum >= 0 {
+		fmt.Fprintf(&b, "line %d, ", e.LineNum+1)
 	}
-	fmt.Fprintf(&b, "column %d:\n%s\n", e.column+1, e.line)
-	for k := 0; k < e.column; k++ {
-		if k >= e.column-4 && k != e.column-1 {
+	fmt.Fprintf(&b, "column %d:\n", e.Column+1)
+	b.WriteString(e.ParseErrorContext())
+	return b.String()
+}
+
+func (e *Error) ParseErrorContext() string {
+	var b strings.Builder
+	b.WriteString(e.line + "\n")
+	for k := 0; k < e.Column; k++ {
+		if k >= e.Column-4 && k != e.Column-1 {
 			b.WriteByte('=')
 		} else {
 			b.WriteByte(' ')