fish_indent: Correct certain comment indenting

Prior to this change, when emitting gap text (comments, newlines, etc),
fish_indent would use the indentation of the text at the end of the gap.
But this has the wrong result for this case:

    begin
    command
    # comment
    end

as the comment would get the indent of the 'end'. Instead use the indent
computed for the gap text itself.

Addresses one case of #7252.

src/fish_indent.cpp

@@ -470,12 +470,19 @@ struct pretty_printer_t {
     // Emit the gap text before a source range.
     void emit_gap_text_before(source_range_t r, gap_flags_t flags) {
         assert(r.start <= source.size() && "source out of bounds");
-        uint32_t start = r.start;
-        if (start < indents.size()) current_indent = indents.at(start);
-
         // Find the gap text which ends at start.
-        source_range_t range = gap_text_to(start);
+        source_range_t range = gap_text_to(r.start);
         if (range.length > 0) {
+            // Set the indent from the beginning of this gap text.
+            // For example:
+            // begin
+            //    cmd
+            //    # comment
+            // end
+            // Here the comment is the gap text before the end, but we want the indent from the
+            // command.
+            if (range.start < indents.size()) current_indent = indents.at(range.start);
+
             // If this range contained an error, append the gap text without modification.
             // For example in: echo foo "
             // We don't want to mess with the quote.

tests/checks/indent.fish

@@ -226,6 +226,28 @@ echo < stdin >>appended yes 2>&1 no > stdout maybe 2>&    4 | cat 2>| cat
 ' | $fish_indent
 #CHECK: echo <stdin >>appended yes 2>&1 no >stdout maybe 2>&4 | cat 2>| cat
 
+
+# issue 7252
+echo -n '
+begin
+# comment
+end
+' | $fish_indent
+#CHECK: begin
+#CHECK: {{    }}# comment
+#CHECK: end
+
+echo -n '
+begin
+cmd
+# comment
+end
+' | $fish_indent
+#CHECK: begin
+#CHECK: {{    }}cmd
+#CHECK: {{    }}# comment
+#CHECK: end
+
 echo -n '
 i\
 f true