From 460509880776c180f6a52a4079c63ef5717fb21e Mon Sep 17 00:00:00 2001
From: Novan <25704935+nofun97@users.noreply.github.com>
Date: Fri, 14 Jan 2022 13:35:21 +1100
Subject: [PATCH] retain initial spaces in string expressions (#243)

Initially, any whitespaces after the opening quote in a string expression
are trimmed. This was meant only for indentations but it also removes
whitespaces that are just spaces. This commit changes that behavior
to retain initial spaces after the opening quote.
---
 syntax/compile_xstr.go      |  8 ++++++++
 syntax/parse_string_test.go | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/syntax/compile_xstr.go b/syntax/compile_xstr.go
index 53ed8faa..f1d341c2 100644
--- a/syntax/compile_xstr.go
+++ b/syntax/compile_xstr.go
@@ -17,6 +17,7 @@ var (
 	indentRE      = regexp.MustCompile(`(\n[\t ]*)\z`)
 	firstIndentRE = regexp.MustCompile(`\A((\n[\t ]+)(?:\n)|(\n))`)
 	lastSpacesRE  = regexp.MustCompile(`\n([ \t]*)\z`)
+	spaces        = regexp.MustCompile(`\A[\t ]+`)
 )
 
 func (pc ParseContext) compileExpandableString(ctx context.Context, b ast.Branch, c ast.Children) (rel.Expr, error) {
@@ -25,6 +26,13 @@ func (pc ParseContext) compileExpandableString(ctx context.Context, b ast.Branch
 	parts := []interface{}{}
 
 	ws := quote[2:]
+
+	// retain initial spaces
+	if spaces.MatchString(ws) {
+		parts = append(parts, ws)
+		ws = ""
+	}
+
 	trim := ""
 	trimIndent := func(s string) {
 		s = ws + s
diff --git a/syntax/parse_string_test.go b/syntax/parse_string_test.go
index a85725bd..f3ce7fa9 100644
--- a/syntax/parse_string_test.go
+++ b/syntax/parse_string_test.go
@@ -16,6 +16,18 @@ func TestXStringSimple(t *testing.T) {
 	AssertCodesEvalToSameValue(t, `"a42k3.142z"     `, `$"a${6*7}k${//math.pi:.3f}z"`)
 }
 
+func TestXStringRetainInitialSpaces(t *testing.T) {
+	t.Parallel()
+
+	AssertCodesEvalToSameValue(t, `"    "     `, `$"    "         `)
+	AssertCodesEvalToSameValue(t, `"    x"    `, `$"    x"        `)
+	AssertCodesEvalToSameValue(t, `"     abc" `, `$"     ${'abc'}"`)
+	AssertCodesEvalToSameValue(t, `"      abc"`, `$"     ${$' abc'}"`)
+
+	// suppress empty line
+	AssertCodesEvalToSameValue(t, `""`, `$"     ${''}"`)
+}
+
 func TestXStringBackquote(t *testing.T) {
 	t.Parallel()
 	AssertCodesEvalToSameValue(t, `""      `, "$``")