nix: improve dev workflow

Solves PostgREST#5.

This is done by avoiding building the postgres extension inside the nix
derivation. Instead we build it with `make` on the current directory and
install it on postgres using the upcoming postgres
`extension_control_path` GUC.

This is taken from the patch on
https://www.postgresql.org/message-id/flat/E7C7BFFB-8857-48D4-A71F-88B359FADCFD%40justatheory.com
and backpatched to postgres 12, 13, 14, 15 and 16,

Thanks to this, it's now possible to do watch commands:

```
nxpg-watch nxpg-16 nxpg-build (rebuilds when changing sources)

nxpg-watch nxpg-13 nxpg-tmp nxpg-test (runs tests when changing sources)
```

Future improvements:

* Makes possible to enable code coverage, since the `.gcno` files will
  live outside the nix store.

* It's wasteful to rebuild the patched pgs everytime, later on this
  `nxpg` could live in another repo and benefit from Nix caching.

Additionally:

* removes clean_generated in favor of builtin EXTRA_CLEAN

* Don't hardcode sources in Makefile

* Update github action

.github/workflows/ci.yaml

@@ -18,6 +18,8 @@ jobs:
         with:
           nix_path: nixpkgs=channel:nixos-unstable
       - name: Run tests
-        run: nix-shell --run "with-pg-${{ matrix.pg-version }} make installcheck"
+        run: nix-shell --run "nxpg-${{ matrix.pg-version }} nxpg-tmp nxpg-test"
       - if: ${{ failure() }}
-        run: cat output/regression.diffs
+        run: |
+          cat regression.out
+          cat regression.diffs

.gitignore

@@ -4,6 +4,12 @@ results/
 .history
 *.so
 *.bc
+*.gcda
+*.gcno
 tags
 plmustache.control
-sql/plmustache--*.sql
+plmustache--*.sql
+coverage.info
+coverage_html
+regression.diffs
+regression.out

Makefile

@@ -1,36 +1,32 @@
+## Our variables
 EXTENSION = plmustache
 EXTVERSION = 0.1
+SED ?= sed
 
-DATA = $(wildcard sql/*--*.sql)
+## PGXS variables
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
 
 MODULE_big = $(EXTENSION)
-OBJS = src/plmustache.o src/observation.o src/build.o
+SRC = $(wildcard src/*.c)
+OBJS = $(patsubst src/%.c, src/%.o, $(SRC))
+SHLIB_LINK = -lmustach
+PG_CFLAGS = -std=c99 -Wno-declaration-after-statement -Wall -Werror -Wshadow
 
 TESTS = $(wildcard test/sql/*.sql)
 REGRESS = $(patsubst test/sql/%.sql,%,$(TESTS))
 REGRESS_OPTS = --inputdir=test
 
-PG_CONFIG = pg_config
-SHLIB_LINK = -lmustach
-
-PG_CFLAGS = -std=c99 -Wno-declaration-after-statement -Wall -Werror -Wshadow
-
-PGXS := $(shell $(PG_CONFIG) --pgxs)
-
-all: sql/$(EXTENSION)--$(EXTVERSION).sql $(EXTENSION).control
+DATA = $(wildcard *--*.sql)
 
-.PHONY: clean_generated
-clean_generated:
-	rm -f $(EXTENSION).control
-	rm -f sql/$(EXTENSION)--$(EXTVERSION).sql
+EXTRA_CLEAN = $(EXTENSION)--$(EXTVERSION).sql $(EXTENSION).control
 
-# extra dep for clean target in pgxs.mk
-clean: clean_generated
+all: $(EXTENSION)--$(EXTVERSION).sql $(EXTENSION).control
 
-sql/$(EXTENSION)--$(EXTVERSION).sql: sql/$(EXTENSION).sql
+$(EXTENSION)--$(EXTVERSION).sql: sql/$(EXTENSION).sql
 	cp $< $@
 
 $(EXTENSION).control:
-	sed "s/@EXTVERSION@/$(EXTVERSION)/g" $(EXTENSION).control.in > $(EXTENSION).control
+	$(SED) "s/@EXTVERSION@/$(EXTVERSION)/g" $(EXTENSION).control.in > $@
 
 include $(PGXS)

nix/nxpg.nix

@@ -0,0 +1,85 @@
+{ writeShellScriptBin, findutils, entr, callPackage, postgresql_16, postgresql_15, postgresql_14, postgresql_13, postgresql_12 } :
+let
+  prefix = "nxpg";
+  supportedPgs = [
+    postgresql_16
+    postgresql_15
+    postgresql_14
+    postgresql_13
+    postgresql_12
+  ];
+  build =
+    writeShellScriptBin "${prefix}-build" ''
+      set -euo pipefail
+
+      make clean
+      make
+    '';
+  test =
+    writeShellScriptBin "${prefix}-test" ''
+      set -euo pipefail
+
+      make clean
+      make
+      make installcheck
+    '';
+
+  watch =
+    writeShellScriptBin "${prefix}-watch" ''
+      set -euo pipefail
+
+      ${findutils}/bin/find . -type f \( -name '*.c' -o -name '*.h' \) | ${entr}/bin/entr -dr "$@"
+    '';
+
+  tmpDb =
+    writeShellScriptBin "${prefix}-tmp" ''
+      set -euo pipefail
+
+      export tmpdir="$(mktemp -d)"
+
+      export PGDATA="$tmpdir"
+      export PGHOST="$tmpdir"
+      export PGUSER=postgres
+      export PGDATABASE=postgres
+
+      trap 'pg_ctl stop -m i && rm -rf "$tmpdir"' sigint sigterm exit
+
+      PGTZ=UTC initdb --no-locale --encoding=UTF8 --nosync -U "$PGUSER"
+
+      # pg versions older than 16 don't support adding "-c" to initdb to add these options
+      # so we just modify the resulting postgresql.conf to avoid an error
+      echo "dynamic_library_path='\$libdir:$(pwd)'" >> $PGDATA/postgresql.conf
+      echo "extension_control_path='\$system:$(pwd)'" >> $PGDATA/postgresql.conf
+
+      default_options="-F -c listen_addresses=\"\" -k $PGDATA"
+
+      pg_ctl start -o "$default_options"
+
+      "$@"
+    '';
+    allPgPaths = map (pg:
+      let
+        ver = builtins.head (builtins.splitVersion pg.version);
+        patchedPg = pg.overrideAttrs(oldAttrs: {
+          patches = oldAttrs.patches ++ [
+            ./patches/${ver}-add-extension_control_path-for.patch
+          ];
+        });
+        script = ''
+          set -euo pipefail
+
+          export PATH=${patchedPg}/bin:"$PATH"
+
+          "$@"
+        '';
+      in
+      writeShellScriptBin "${prefix}-${ver}" script
+    ) supportedPgs;
+in
+[
+  build
+  test
+  watch
+  tmpDb
+  allPgPaths
+]