opt: compute join output col map properly

Fixes cockroachdb#39010.

This manifested with the advent of WITH, but the problem was actually
that we were computing a join output map somewhat incorrectly. This
never actually caused problems before because we would prune any columns
that could cause there to be a disparity between the two ways of
computing the size of the ColMap, but since WITH doesn't support
pruning, it caused issues.

I also replaced some other uses of Len that were potentially sketchy.

Release note: None

pkg/sql/opt/exec/execbuilder/relational.go

@@ -67,7 +67,13 @@ type execPlan struct {
 // if the node outputs the same optimizer ColumnID multiple times.
 // TODO(justin): we should keep track of this instead of computing it each time.
 func (ep *execPlan) numOutputCols() int {
-	max, ok := ep.outputCols.MaxValue()
+	return numOutputColsInMap(ep.outputCols)
+}
+
+// numOutputColsInMap returns the number of slots required to fill in all of
+// the columns referred to by this ColMap.
+func numOutputColsInMap(m opt.ColMap) int {
+	max, ok := m.MaxValue()
 	if !ok {
 		return 0
 	}
@@ -512,6 +518,7 @@ func (b *Builder) buildProject(prj *memo.ProjectExpr) (execPlan, error) {
 	if err != nil {
 		return execPlan{}, err
 	}
+
 	projections := prj.Projections
 	if len(projections) == 0 {
 		// We have only pass-through columns.
@@ -633,7 +640,7 @@ func (b *Builder) buildApplyJoin(join memo.RelExpr) (execPlan, error) {
 	allCols := joinOutputMap(left.outputCols, fakeRight.outputCols)
 
 	ctx := buildScalarCtx{
-		ivh:     tree.MakeIndexedVarHelper(nil /* container */, allCols.Len()),
+		ivh:     tree.MakeIndexedVarHelper(nil /* container */, numOutputColsInMap(allCols)),
 		ivarMap: allCols,
 	}
 
@@ -771,7 +778,7 @@ func (b *Builder) initJoinBuild(
 	allCols := joinOutputMap(leftPlan.outputCols, rightPlan.outputCols)
 
 	ctx := buildScalarCtx{
-		ivh:     tree.MakeIndexedVarHelper(nil /* container */, allCols.Len()),
+		ivh:     tree.MakeIndexedVarHelper(nil /* container */, numOutputColsInMap(allCols)),
 		ivarMap: allCols,
 	}
 
@@ -792,7 +799,8 @@ func (b *Builder) initJoinBuild(
 // joinOutputMap determines the outputCols map for a (non-semi/anti) join, given
 // the outputCols maps for its inputs.
 func joinOutputMap(left, right opt.ColMap) opt.ColMap {
-	numLeftCols := left.Len()
+	numLeftCols := numOutputColsInMap(left)
+
 	res := left.Copy()
 	right.ForEach(func(colIdx, rightIdx int) {
 		res.Set(colIdx, rightIdx+numLeftCols)

pkg/sql/opt/exec/execbuilder/testdata/with

@@ -68,3 +68,42 @@ root                                       ·              ·                 (a
 ·                                          size           2 columns, 1 row  ·                   ·
 ·                                          row 0, expr 0  1                 ·                   ·
 ·                                          row 0, expr 1  unique_rowid()    ·                   ·
+
+# Regression test for #39010.
+
+statement ok
+CREATE TABLE table39010 (col NAME)
+
+query TTTTT
+EXPLAIN (VERBOSE)
+  WITH
+    w AS (SELECT NULL, NULL FROM table39010)
+  SELECT
+    col
+  FROM
+    w, table39010
+----
+root                                  ·             ·                                  (col)                          ·
+ ├── render                           ·             ·                                  (col)                          ·
+ │    │                               render 0      col                                ·                              ·
+ │    └── hash-join                   ·             ·                                  ("?column?", "?column?", col)  ·
+ │         │                          type          cross                              ·                              ·
+ │         ├── render                 ·             ·                                  ("?column?", "?column?")       ·
+ │         │    │                     render 0      "?column?"                         ·                              ·
+ │         │    │                     render 1      "?column?"                         ·                              ·
+ │         │    └── scan buffer node  ·             ·                                  ("?column?")                   ·
+ │         │                          label         buffer 1 (w)                       ·                              ·
+ │         └── scan                   ·             ·                                  (col)                          ·
+ │                                    table         table39010@primary                 ·                              ·
+ │                                    spans         ALL                                ·                              ·
+ └── subquery                         ·             ·                                  (col)                          ·
+      │                               id            @S1                                ·                              ·
+      │                               original sql  SELECT NULL, NULL FROM table39010  ·                              ·
+      │                               exec mode     all rows                           ·                              ·
+      └── buffer node                 ·             ·                                  ("?column?")                   ·
+           │                          label         buffer 1 (w)                       ·                              ·
+           └── render                 ·             ·                                  ("?column?")                   ·
+                │                     render 0      NULL                               ·                              ·
+                └── scan              ·             ·                                  ()                             ·
+·                                     table         table39010@primary                 ·                              ·
+·                                     spans         ALL                                ·                              ·