feat(format): skip non-plpgsql bodies; keep literals and embedded code safe

- Only restyle bodies for plpgsql/sql; skip pl* (plpython3u, plperl, ...), c and internal
- Keep LANGUAGE clause on DO blocks
- Carry multi-line string and dollar-quoted literals verbatim in bodies and DML
- Format dollar-quoted literals that contain code (declare/begin/select/...), never format() templates
- Fix code joined onto -- comments, early flush after raise exception, dropped comment before BEGIN
- Regenerate test_mm_proc golden; document in README, plan, todo

pkg/format/format_test.go

@@ -200,3 +200,85 @@ func TestCorpusIdempotentAndSafe(t *testing.T) {
 func semanticallyEqual(a, b string) bool {
 	return SemanticallyEqual(a, b)
 }
+
+func TestNonPlpgsqlBodyVerbatim(t *testing.T) {
+	body := "$$\ndeclare x = 1\nbegin = 2\n$$"
+	src := "create function f() returns void as " + body + " language plpython3u;"
+	if out := format(src); !strings.Contains(out, body) {
+		t.Fatalf("plpython3u body was modified:\n%s", out)
+	}
+}
+
+func TestLanguageBodyGate(t *testing.T) {
+	body := "$$\ndeclare x int:=1;\nbegin\nnull;\nend\n$$"
+	for lang, verbatim := range map[string]bool{"plpgsql": false, "sql": false, "plpython3u": true, "plperl": true, "pltcl": true, "c": true, "internal": true} {
+		out := format("create function f() returns void as " + body + " language " + lang + ";")
+		if got := strings.Contains(out, body); got != verbatim {
+			t.Errorf("language %s: verbatim=%v, want %v\n%s", lang, got, verbatim, out)
+		}
+	}
+}
+
+func TestDoBlockLanguageGate(t *testing.T) {
+	body := "$$\ndeclare x int:=1;\nbegin\nnull;\nend\n$$"
+	for src, verbatim := range map[string]bool{
+		"do " + body + ";":                     false,
+		"do language plpgsql " + body + ";":    false,
+		"do " + body + " language plpgsql;":    false,
+		"do language plpython3u " + body + ";": true,
+		"do " + body + " language plperl;":     true,
+	} {
+		if out := format(src); strings.Contains(out, body) != verbatim {
+			t.Errorf("%q: verbatim=%v, want %v\n%s", src, !verbatim, verbatim, out)
+		}
+	}
+}
+
+func TestDoBlockKeepsLanguageClause(t *testing.T) {
+	for _, src := range []string{
+		"do language plpython3u $$\nx = 1\n$$;",
+		"do $$\nx = 1\n$$ language plpython3u;",
+	} {
+		if out := format(src); !strings.Contains(strings.ToLower(out), "language plpython3u") {
+			t.Errorf("LANGUAGE clause lost:\n%s", out)
+		}
+	}
+}
+
+func TestMultiLineStringLiteralVerbatim(t *testing.T) {
+	src := "create function f() returns void language plpgsql as $$\nDECLARE\n  x int;\nBEGIN\n  if x = 1 then\n    raise exception E'A client\nTo resolve this', NEW.id;\n  end if;\nEND\n$$;"
+	if out := format(src); !strings.Contains(out, "E'A client\nTo resolve this'") {
+		t.Errorf("multi-line string was reindented:\n%s", out)
+	}
+}
+
+func TestCommentBeforeBeginKept(t *testing.T) {
+	src := "create function f() returns void language plpgsql as $$\nDECLARE\n  x int = 1;  --0=old, 1=new\nBEGIN\n  null;\nEND\n$$;"
+	out := format(src)
+	if !strings.Contains(out, "--0=old, 1=new") {
+		t.Fatalf("comment before BEGIN lost:\n%s", out)
+	}
+	if again := format(out); again != out {
+		t.Fatalf("not idempotent:\n%s\n---\n%s", out, again)
+	}
+}
+
+func TestEmbeddedDollarLiterals(t *testing.T) {
+	body := func(lit string) string {
+		return "create function f() returns void language plpgsql as $$\nDECLARE\n  x text;\nBEGIN\n  x = " + lit + ";\nEND\n$$;"
+	}
+	// format() template: must be untouched.
+	tmpl := "format($Q$select %s, %3$s from t$Q$, a)"
+	if out := format(body(tmpl)); !strings.Contains(out, "$Q$select %s, %3$s from t$Q$") {
+		t.Errorf("placeholder template modified:\n%s", out)
+	}
+	// SQL fragment (not a statement): untouched.
+	frag := "$s$ and (a=1)  or b=2 $s$"
+	if out := format(body(frag)); !strings.Contains(out, frag) {
+		t.Errorf("fragment modified:\n%s", out)
+	}
+	// Statement: formatted as code.
+	if out := format(body("$q$select a,b from t where x=1$q$")); strings.Contains(out, "$q$select a,b from t where x=1$q$") {
+		t.Errorf("embedded select was not formatted:\n%s", out)
+	}
+}