Retain leading spaces in non-expanding braces

This makes two changes:

1. Remove the 'brace_text_start' idea. The idea of 'brace_text_start' was
to prevent emitting `BRACE_SPACE` at the beginning or end of an item. But
we later strip these off anyways, so there is no apparent benefit. If we
are not doing brace expansion, this prevented emitting whitespace at the
beginning or end of an item, leading to #6564.

2. When performing brace expansion, only stomp the space character with
`BRACE_SPACE`; do not stomp newlines and tabs. This is because the fix in
came from a newline or tab literal, then we would have effectively
replaced a newline or tab with a space, so this is important for #6564 as
well. Moreover, it is not easy to place a literal newline or tab inside a
brace expansion, and users who do probably do not mean for it to be
stripped, so I believe this is a good change in general.

Fixes #6564

src/common.cpp

@@ -1435,7 +1435,6 @@ static bool unescape_string_internal(const wchar_t *const input, const size_t in
     // The positions of variable expansions or brace ","s.
     // We only read braces as expanders if there's a variable expansion or "," in them.
     std::vector<size_t> vars_or_seps;
-    bool brace_text_start = false;
     int brace_count = 0;
 
     bool errored = false;
@@ -1531,7 +1530,6 @@ static bool unescape_string_internal(const wchar_t *const input, const size_t in
                         // assert(brace_count > 0 && "imbalanced brackets are a tokenizer error, we
                         // shouldn't be able to get here");
                         brace_count--;
-                        brace_text_start = brace_text_start && brace_count > 0;
                         to_append_or_none = BRACE_END;
                         if (!braces.empty()) {
                             // If we didn't have a var or separator since the last '{',
@@ -1559,17 +1557,13 @@ static bool unescape_string_internal(const wchar_t *const input, const size_t in
                 case L',': {
                     if (unescape_special && brace_count > 0) {
                         to_append_or_none = BRACE_SEP;
-                        brace_text_start = false;
                         vars_or_seps.push_back(input_position);
                     }
                     break;
                 }
-                case L'\n':
-                case L'\t':
                 case L' ': {
                     if (unescape_special && brace_count > 0) {
-                        to_append_or_none =
-                            brace_text_start ? maybe_t<wchar_t>(BRACE_SPACE) : none();
+                        to_append_or_none = BRACE_SPACE;
                     }
                     break;
                 }
@@ -1586,9 +1580,6 @@ static bool unescape_string_internal(const wchar_t *const input, const size_t in
                     break;
                 }
                 default: {
-                    if (unescape_special && brace_count > 0) {
-                        brace_text_start = true;
-                    }
                     break;
                 }
             }

tests/checks/braces.fish

@@ -0,0 +1,50 @@
+#RUN: %fish %s
+
+echo x-{1}
+#CHECK: x-{1}
+
+echo x-{1,2}
+#CHECK: x-1 x-2
+
+echo foo-{1,2{3,4}}
+#CHECK: foo-1 foo-23 foo-24
+
+echo foo-{} # literal "{}" expands to itself
+#CHECK: foo-{}
+
+echo foo-{{},{}} # the inner "{}" expand to themselves, the outer pair expands normally.
+#CHECK: foo-{} foo-{}
+
+echo foo-{{a},{}} # also works with something in the braces.
+#CHECK: foo-{a} foo-{}
+
+echo foo-{""} # still expands to foo-{}
+#CHECK: foo-{}
+
+echo foo-{$undefinedvar} # still expands to nothing
+#CHECK: 
+
+echo foo-{,,,} # four empty items in the braces.
+#CHECK: foo- foo- foo- foo-
+
+echo foo-{,\,,} # an empty item, a "," and an empty item.
+#CHECK: foo- foo-, foo-
+
+echo .{  foo  bar  }. # see 6564
+#CHECK: .{  foo  bar  }.
+
+# whitespace within entries is retained
+for foo in {a, hello
+wo  rld }
+    echo \'$foo\'
+end
+# CHECK: 'a'
+# CHECK: 'hello
+# CHECK: wo  rld'
+
+for foo in {hello
+world}
+   echo \'$foo\'
+end
+#CHECK: '{hello
+#CHECK: world}'

tests/parameter_expansion.in

@@ -14,12 +14,6 @@ echo \'{ hello , world }\'
 for phrase in {good\,,   beautiful ,morning}; echo -n "$phrase "; end | string trim;
 for phrase in {goodbye\,,\ cruel\ ,world\n}; echo -n $phrase; end;
 
-# whitespace within entries converted to spaces in a single entry
-for foo in {a, hello
-world }
-	echo \'$foo\'
-end
-
 # dual expansion cartesian product
 echo { alpha, beta }\ {lambda, gamma }, |  string replace -r ',$' ''
 

tests/parameter_expansion.out

@@ -6,8 +6,6 @@ apple orange banana
 'hello' 'world'
 good, beautiful morning
 goodbye, cruel world
-'a'
-'hello world'
 alpha lambda, beta lambda, alpha gamma, beta gamma
 Meg
 Jo

tests/test1.err

@@ -2,9 +2,6 @@
 ####################
 # Comments in odd places don't cause problems
 
-####################
-# Brace expansion
-
 ####################
 # Escaped newlines
 

tests/test1.in

@@ -11,21 +11,6 @@ for i in 1 2 # Comment on same line as command
 	end;
 end
 
-logmsg Brace expansion
-echo x-{1}
-echo x-{1,2}
-echo foo-{1,2{3,4}}
-
-echo foo-{} # literal "{}" expands to itself
-echo foo-{{},{}} # the inner "{}" expand to themselves, the outer pair expands normally.
-echo foo-{{a},{}} # also works with something in the braces.
-echo foo-{""} # still expands to foo-{}
-echo banana # just as a marker
-echo foo-{$undefinedvar} # still expands to nothing
-
-echo foo-{,,,} # four empty items in the braces.
-echo foo-{,\,,} # an empty item, a "," and an empty item.
-
 logmsg Escaped newlines
 echo foo\ bar
 echo foo\

tests/test1.out

@@ -6,20 +6,6 @@
 2a
 2b
 
-####################
-# Brace expansion
-x-{1}
-x-1 x-2
-foo-1 foo-23 foo-24
-foo-{}
-foo-{} foo-{}
-foo-{a} foo-{}
-foo-{}
-banana
-
-foo- foo- foo- foo-
-foo- foo-, foo-
-
 ####################
 # Escaped newlines
 foo bar