feat(dev): Enhance Makefile for faster go-code with scoping

[dkrotx]

What changed?
Addressing #7737:

• Updated the pr target to allow optional scoping for go-generate using the GEN_DIR variable.
• Modified the go-generate command to reflect the new scope in its output message.

Why?
This change provides developers with the ability to specify a directory scope for code generation, improving flexibility and usability when running code generation tasks.
We extensively use go-generate, and it is slow on the entire cadence
repo, which extends make pr up to 5 mins.
With GEN_DIR=service/matching make pr takes less than a minute.

How did you test it?
No specific tests were added, but existing Makefile targets were verified to ensure they function correctly with the new changes.
make pr GEN_DIR=service/matching # works <1min comparing with the
original 4 mins

Potential risks
No: it's a new optional flag for dev-only Makefile' goal

Release notes

Documentation Changes
Extended make help (or just make w/o goal) to have the example for the "pr" goal.

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Reviewer Validation

PR Description Quality (check these before reviewing code):

• "What changed" provides a clear 1-2 line summary
  • Project Issue is linked
• "Why" explains the full motivation with sufficient context
• Testing is documented:
  • Unit test commands are included (with exact go test invocation)
  • Integration test setup/commands included (if integration tests were run)
  • Canary testing details included (if canary was mentioned)
• Potential risks section is thoughtfully filled out (or legitimately N/A)
• Release notes included if this completes a user-facing feature
• Documentation needs are addressed (or noted if uncertain)

[gitar-bot]

Code Review ✅ Approved 1 resolved / 1 findings

Clean, backward-compatible enhancement to scope go generate via GEN_DIR. The self-referencing variable issue from the prior review has been fixed with override and := simple expansion. No new issues found.

✅ 1 resolved

✅ Bug: Self-referencing recursive variable breaks make pr and make go-generate

📄 Makefile:481
Using = (recursively-expanded assignment) for GEN_DIR on line 481 creates a self-referencing variable that causes GNU Make to error when GEN_DIR is not provided:

Makefile:481: *** Recursive variable 'GEN_DIR' references itself (eventually).  Stop.

This breaks the default (no-argument) invocation of both make pr and make go-generate, which is the primary usage path. The release target is also affected since it calls go-generate without GEN_DIR.

I reproduced this locally with make go-generate --dry-run and make pr --dry-run — both fail at line 481.

Additionally, even when GEN_DIR is provided on the command line (e.g., make pr GEN_DIR=service/matching/), the patsubst normalization doesn't take effect because command-line variables override Makefile = assignments, so trailing slashes are not stripped.

Fix: Use override with := (simply-expanded assignment):

override GEN_DIR := $(patsubst %/,%,$(strip $(GEN_DIR)))

This resolves both issues:

1. No self-reference error when GEN_DIR is empty
2. patsubst correctly strips trailing slashes even when GEN_DIR is passed on the command line

Verified all three cases work with the fix:

• make go-generate → uses ./... ✓
• make go-generate GEN_DIR=service/matching → uses ./service/matching/... ✓
• make go-generate GEN_DIR=service/matching/ → uses ./service/matching/... (slash stripped) ✓

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