execgen: try not to touch .eg.go files

This changes the Makefile to output .eg.go output to a tmp file before
actually editing .eg.go files, to prevent build churn.

Also, fix a bug in one of the generators that causes it to output
generated code in an inconsistent (but semantically identical) manner.

Release note: None

Makefile

@@ -1536,7 +1536,8 @@ pkg/sql/colexec/vec_comparators.eg.go: pkg/sql/colexec/vec_comparators_tmpl.go
 pkg/sql/colexec/window_peer_grouper.eg.go: pkg/sql/colexec/window_peer_grouper_tmpl.go
 
 $(EXECGEN_TARGETS): bin/execgen
-	execgen $@
+	execgen $@ > $@.tmp; cmp $@.tmp $@ && rm -f $@.tmp || mv $@.tmp $@
+
 
 optgen-defs := pkg/sql/opt/ops/*.opt
 optgen-norm-rules := pkg/sql/opt/norm/rules/*.opt

pkg/sql/colexec/execgen/cmd/execgen/main.go

@@ -84,7 +84,7 @@ func (g *execgen) run(args ...string) bool {
 			g.reportError(errors.Errorf("unrecognized filename: %s", file))
 			return false
 		}
-		if err := g.generate(gen, out); err != nil {
+		if err := g.generate(gen); err != nil {
 			g.reportError(err)
 			return false
 		}
@@ -96,7 +96,7 @@ func (g *execgen) run(args ...string) bool {
 var emptyCommentRegex = regexp.MustCompile(`[ \t]*//[ \t]*\n`)
 var emptyBlockCommentRegex = regexp.MustCompile(`[ \t]*/\*[ \t]*\*/[ \t]*\n`)
 
-func (g *execgen) generate(genFunc generator, out string) error {
+func (g *execgen) generate(genFunc generator) error {
 	var buf bytes.Buffer
 	buf.WriteString("// Code generated by execgen; DO NOT EDIT.\n")
 
@@ -122,23 +122,12 @@ func (g *execgen) generate(genFunc generator, out string) error {
 		b = buf.Bytes()
 	}
 
+	// Ignore any write error if another error already occurred.
+	_, writeErr := os.Stdout.Write(b)
 	if err != nil {
-		// Ignore any write error if another error already occurred.
-		_ = g.writeOutputFile(b, out)
 		return err
 	}
-	return g.writeOutputFile(b, out)
-}
-
-func (g *execgen) writeOutputFile(b []byte, out string) error {
-	file, err := os.Create(out)
-	if err != nil {
-		return err
-	}
-	defer file.Close()
-
-	_, err = file.Write(b)
-	return err
+	return writeErr
 }
 
 // usage is a replacement usage function for the flags package.

pkg/sql/colexec/execgen/cmd/execgen/rowstovec_gen.go

@@ -13,6 +13,7 @@ package main
 import (
 	"io"
 	"io/ioutil"
+	"sort"
 	"strings"
 	"text/template"
 
@@ -97,8 +98,15 @@ func genRowsToVec(wr io.Writer) error {
 
 	columnConversions := make([]columnConversion, 0, len(conversionsMap))
 	for _, conversion := range conversionsMap {
+		sort.Slice(conversion.Widths, func(i, j int) bool {
+			return conversion.Widths[i].Width < conversion.Widths[j].Width
+		})
 		columnConversions = append(columnConversions, *conversion)
 	}
+	// Sort the list so that we output in a consistent order.
+	sort.Slice(columnConversions, func(i, j int) bool {
+		return strings.Compare(columnConversions[i].Family, columnConversions[j].Family) < 0
+	})
 	return tmpl.Execute(wr, columnConversions)
 }