execgen: permit customization of template path

[jordanlewis]

Closes #56982

This commit adds a new argument to execgen, -template, which allows
customization of the file path of the input template for a given output
file.

Here's an example of how to run execgen with cutomized paths:

execgen -template path/to/template_tmpl.go path/to/eventual/generated/code.eg.go > path/to/wherever/you/want/to/write/the/file.eg.o

The second argument is important because it is used as an argument to
goimports, which needs to the actual, eventual path that the generated
code will live at. Note that it doesn't actually need to write to that
filepath - just needs to know what the name will be, eventually.

Release note: None

[cockroach-teamcity]

This change is 

[jordanlewis]

@irfansharif I don't necessarily need a review, but please LMK if the proposed change would fix the Bazel issue.

[irfansharif]

This works. Sorry for the delay, wanted to see what the bazel rules would change to.

diff --git i/pkg/sql/colexec/BUILD.bazel w/pkg/sql/colexec/BUILD.bazel
index ff48f4de4d..a39d8b0eea 100644
--- i/pkg/sql/colexec/BUILD.bazel
+++ w/pkg/sql/colexec/BUILD.bazel
@@ -52,6 +52,7 @@ go_library(
         "unordered_distinct.go",
         "utils.go",
         ":gen-exec",  # keep
+        ":gen-and-or-projection",  # keep
     ],
     importpath = "github.com/cockroachdb/cockroach/pkg/sql/colexec",
     visibility = ["//visibility:public"],
@@ -201,7 +202,6 @@ go_test(

 # Define a file group for all the .eg.go targets.
 targets = [
-    "and_or_projection.eg.go",
     "cast.eg.go",
     "const.eg.go",
     "default_cmp_expr.eg.go",
@@ -254,3 +254,15 @@ generate(
     targets = targets,
     templates = glob(["*_tmpl.go"]),
 )
+
+# XXX: Rule generation for and_or_projection.eg.go. We'll want one per eg.go
+# file; we'll write a helper method to make it look nicer.
+genrule(
+    name = "gen-and-or-projection",
+    srcs = ["and_or_projection_tmpl.go"],
+    outs = ["and_or_projection.eg.go"],
+    cmd = """
+      $(location //pkg/sql/colexec/execgen/cmd/execgen) -template $(location and_or_projection_tmpl.go) -fmt=false pkg/sql/colexec/and_or_projection.eg.go > $@
+      $(location //vendor/github.com/cockroachdb/gostdlib/x/tools/cmd/goimports) -w $@
+    """,
+    tools = ["//pkg/sql/colexec/execgen/cmd/execgen", "//vendor/github.com/cockroachdb/gostdlib/x/tools/cmd/goimports"],
+)

[jordanlewis]

Nice - that seems pretty close to the optgen one, so victory?

I'm happy to help out with creating the genrules if it's annoying, if you tell me how to do it.

bors r+

[craig]

Build succeeded:

• GitHub CI (Cockroach)

[irfansharif]

I'm happy to help out with creating the genrules if it's annoying.

Not annoying at all, thanks for helping me out here Jordan. See #57075.