From 55640a36aeaf2f9d8b303903742c31fc382d7ac9 Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Thu, 22 Jan 2026 22:38:32 +0000
Subject: [PATCH] Makefile: dependency generation

My previous idea was to generate a list of all the headers, and add it
as a dependency for all object files.  This way, any changes in a
header would trigger a rebuild of all object files, which would
in-turn trigger a build of the binary.

This will be a bit of an issue later on when we have stuff that's
independent of others; a change in parser code won't necessarily
affect code generation, but a change in AST will.  We don't want to
re-trigger builds for everything.

This setup forces gcc to generate a clear set of dependencies in the
build folder (in a syntax recognisable by Make), then include that in
the Makefile itself.  These dependencies are specific to each code
unit and so only concern the headers that code unit uses.
---
 Makefile | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/Makefile b/Makefile
index 62f95b9..24f42a5 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,8 @@ CC=cc
 
 DIST=build
 OUT=$(DIST)/arl.out
+MODULES=main lib/vec lib/sv parser/ast parser/parser
+OBJECTS:=$(patsubst %,$(DIST)/%.o, $(MODULES))
 
 LDFLAGS=
 GFLAGS=-Wall -Wextra -Wpedantic -std=c23 -I./src/
@@ -15,27 +17,26 @@ else
 CFLAGS=$(GFLAGS) $(DFLAGS)
 endif
 
-HEADERS=$(shell find "src" -type 'f' -name '*.h')
-MODULES=main lib/vec lib/sv parser/ast parser/parser
-OBJECTS=$(patsubst %,$(DIST)/%.o, $(MODULES))
+# Dependency generation
+DEPFLAGS=-MT $@ -MMD -MP -MF
+DEPDIR=$(DIST)/deps
 
 $(OUT): $(OBJECTS) | $(DIST)
 	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)
 
-$(DIST)/%.o: src/arl/%.c $(HEADERS) | $(DIST)
-	$(CC) $(CFLAGS) -c -o $@ $<
-
-$(DIST)/%.o: src/arl/parser/%.c $(HEADERS) | $(DIST)
-	$(CC) $(CFLAGS) -c -o $@ $<
-
-$(DIST)/%.o: src/arl/lib/%.c $(HEADERS) | $(DIST)
-	$(CC) $(CFLAGS) -c -o $@ $<
+$(DIST)/%.o: src/arl/%.c | $(DIST) $(DEPDIR)
+	$(CC) $(CFLAGS) $(DEPFLAGS) $(DEPDIR)/$*.d -c -o $@ $<
 
 $(DIST):
 	mkdir -p $(DIST)
 	mkdir -p $(DIST)/lib
 	mkdir -p $(DIST)/parser
 
+$(DEPDIR):
+	mkdir -p $(DEPDIR)
+	mkdir -p $(DEPDIR)/lib
+	mkdir -p $(DEPDIR)/parser
+
 .PHONY: run clean
 ARGS=
 run: $(OUT)
@@ -43,3 +44,6 @@ run: $(OUT)
 
 clean:
 	rm -rf $(DIST)
+
+DEPS:=$(patsubst %,$(DEPDIR)/%.d, $(MODULES))
+include $(wildcard $(DEPS))