fix nix packaging (#440)

* allow configuring embedded postgres binaries path

On NixOS, running dynamically linked programs intended for generic
Linux environments is not possible. This patch allows for configuring
a binary path at build time so that the Postgres version from the
nixpkgs can be used instead.

* configure postgres binary path when building via nix

Author: vkcku

internal/postgres/embedded.go

@@ -17,6 +17,11 @@ import (
 	"github.com/pgplex/pgschema/cmd/util"
 )
 
+// binariesPath is the path that contains the Postgres binaries.
+// This is meant to be injected via ldflags (for example, to use the nix
+// postgres versions when building with nix).
+var binariesPath string
+
 // PostgresVersion is an alias for the embedded-postgres version type.
 type PostgresVersion = embeddedpostgres.PostgresVersion
 
@@ -91,14 +96,16 @@ func StartEmbeddedPostgres(config *EmbeddedPostgresConfig) (*EmbeddedPostgres, e
 		Password(config.Password).
 		Port(uint32(port)).
 		RuntimePath(runtimePath).
+		BinariesPath(binariesPath).
 		DataPath(filepath.Join(runtimePath, "data")).
 		Logger(io.Discard). // Suppress embedded-postgres startup logs
 		StartParameters(map[string]string{
-			"logging_collector":          "off",    // Disable log collector
-			"log_destination":            "stderr", // Send logs to stderr (which we discard)
-			"log_min_messages":           "PANIC",  // Only log PANIC level messages
-			"log_statement":              "none",   // Don't log SQL statements
-			"log_min_duration_statement": "-1",     // Don't log slow queries
+			"logging_collector":          "off",       // Disable log collector
+			"log_destination":            "stderr",    // Send logs to stderr (which we discard)
+			"log_min_messages":           "PANIC",     // Only log PANIC level messages
+			"log_statement":              "none",      // Don't log SQL statements
+			"log_min_duration_statement": "-1",        // Don't log slow queries
+			"unix_socket_directories":    runtimePath, // Use a directory that is guaranteed to exist
 		})
 
 	// Create and start PostgreSQL instance

nix/pgschema.nix

@@ -1,8 +1,9 @@
-{ pkgs ? import <nixpkgs> {}, rev ? "unknown", buildDate ? "unknown" }:
+{ pkgs ? import <nixpkgs> {}, rev ? "unknown", buildDate ? "unknown", postgresql ? null }:
 
 let
   lib = pkgs.lib;
   version = lib.strings.removeSuffix "\n" (builtins.readFile ../internal/version/VERSION);
+  postgres = if postgresql == null then pkgs.postgresql else postgresql;
 in
 pkgs.buildGoModule {
   pname = "pgschema";
@@ -31,6 +32,8 @@ pkgs.buildGoModule {
     "github.com/pgplex/pgschema/cmd.GitCommit=${rev}"
     "-X"
     "github.com/pgplex/pgschema/cmd.BuildDate=${buildDate}"
+    "-X"
+    "github.com/pgplex/pgschema/internal/postgres.binariesPath=${postgres}"
   ];
 
   meta = with lib; {