backend/pg: Accept connection string in PGDATABASE environment variable

internal/backend/remote-state/pg/backend.go

@@ -23,6 +23,7 @@ func New() backend.Backend {
 				Type:        schema.TypeString,
 				Required:    true,
 				Description: "Postgres connection string; a `postgres://` URL",
+				DefaultFunc: schema.EnvDefaultFunc("PGDATABASE", nil),
 			},
 
 			"schema_name": {

internal/backend/remote-state/pg/backend_test.go

@@ -7,13 +7,15 @@ import (
 	"database/sql"
 	"fmt"
 	"os"
+	"strings"
 	"testing"
 
+	"github.com/hashicorp/hcl/v2/hcldec"
 	"github.com/hashicorp/terraform/internal/backend"
 	"github.com/hashicorp/terraform/internal/states/remote"
 	"github.com/hashicorp/terraform/internal/states/statemgr"
+	"github.com/hashicorp/terraform/internal/tfdiags"
 	"github.com/lib/pq"
-	_ "github.com/lib/pq"
 )
 
 // Function to skip a test unless in ACCeptance test mode.
@@ -38,13 +40,46 @@ func TestBackend_impl(t *testing.T) {
 func TestBackendConfig(t *testing.T) {
 	testACC(t)
 	connStr := getDatabaseUrl()
-	schemaName := pq.QuoteIdentifier(fmt.Sprintf("terraform_%s", t.Name()))
 
-	config := backend.TestWrapConfig(map[string]interface{}{
+	testCases := []struct {
+		Name        string
+		EnvVars     map[string]string
+		Config      map[string]interface{}
+		ExpectError string
+	}{
+		{
+			Name: "valid-config",
+			Config: map[string]interface{}{
 				"conn_str":    connStr,
-		"schema_name": schemaName,
-	})
-	schemaName = pq.QuoteIdentifier(schemaName)
+				"schema_name": fmt.Sprintf("terraform_%s", t.Name()),
+			},
+		},
+		{
+			Name: "missing-conn-str",
+			Config: map[string]interface{}{
+				"schema_name": fmt.Sprintf("terraform_%s", t.Name()),
+			},
+			ExpectError: `The attribute "conn_str" is required, but no definition was found.`,
+		},
+		{
+			Name: "conn-str-env-var",
+			EnvVars: map[string]string{
+				"PGDATABASE": connStr,
+			},
+			Config: map[string]interface{}{
+				"schema_name": fmt.Sprintf("terraform_%s", t.Name()),
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.Name, func(t *testing.T) {
+			for k, v := range tc.EnvVars {
+				t.Setenv(k, v)
+			}
+
+			config := backend.TestWrapConfig(tc.Config)
+			schemaName := pq.QuoteIdentifier(tc.Config["schema_name"].(string))
 
 			dbCleaner, err := sql.Open("postgres", connStr)
 			if err != nil {
@@ -52,7 +87,35 @@ func TestBackendConfig(t *testing.T) {
 			}
 			defer dbCleaner.Query(fmt.Sprintf("DROP SCHEMA IF EXISTS %s CASCADE", schemaName))
 
-	b := backend.TestBackendConfig(t, New(), config).(*Backend)
+			var diags tfdiags.Diagnostics
+			b := New().(*Backend)
+			schema := b.ConfigSchema()
+			spec := schema.DecoderSpec()
+			obj, decDiags := hcldec.Decode(config, spec, nil)
+			diags = diags.Append(decDiags)
+
+			newObj, valDiags := b.PrepareConfig(obj)
+			diags = diags.Append(valDiags.InConfigBody(config, ""))
+
+			if tc.ExpectError != "" {
+				if !diags.HasErrors() {
+					t.Fatal("error expected but got none")
+				}
+				if !strings.Contains(diags.ErrWithWarnings().Error(), tc.ExpectError) {
+					t.Fatalf("failed to find %q in %s", tc.ExpectError, diags.ErrWithWarnings())
+				}
+				return
+			} else if diags.HasErrors() {
+				t.Fatal(diags.ErrWithWarnings())
+			}
+
+			obj = newObj
+
+			confDiags := b.Configure(obj)
+			if len(confDiags) != 0 {
+				confDiags = confDiags.InConfigBody(config, "")
+				t.Fatal(confDiags.ErrWithWarnings())
+			}
 
 			if b == nil {
 				t.Fatal("Backend could not be configured")
@@ -78,6 +141,9 @@ func TestBackendConfig(t *testing.T) {
 			}
 
 			backend.TestBackendStates(t, b)
+		})
+	}
+
 }
 
 func TestBackendConfigSkipOptions(t *testing.T) {
@@ -243,7 +309,7 @@ func TestBackendStates(t *testing.T) {
 			if err != nil {
 				t.Fatal(err)
 			}
-			defer dbCleaner.Query("DROP SCHEMA IF EXISTS %s CASCADE", pq.QuoteIdentifier(schemaName))
+			defer dbCleaner.Query(fmt.Sprintf("DROP SCHEMA IF EXISTS %s CASCADE", pq.QuoteIdentifier(schemaName)))
 
 			config := backend.TestWrapConfig(map[string]interface{}{
 				"conn_str":    connStr,

website/docs/language/settings/backends/pg.mdx

@@ -68,7 +68,7 @@ data "terraform_remote_state" "network" {
 
 The following configuration options or environment variables are supported:
 
-- `conn_str` - (Required) Postgres connection string; a `postgres://` URL
+- `conn_str` - (Required) Postgres connection string; a `postgres://` URL. `conn_str` can also be set using the `PGDATABASE` environment variable.
 - `schema_name` - Name of the automatically-managed Postgres schema, default `terraform_remote_state`.
 - `skip_schema_creation` - If set to `true`, the Postgres schema must already exist. Terraform won't try to create the schema, this is useful when it has already been created by a database administrator.
 - `skip_table_creation` - If set to `true`, the Postgres table must already exist. Terraform won't try to create the table, this is useful when it has already been created by a database administrator.