[bug #52517] adjustment can cause overwritten text on lines using \~

[G. Branden Robinson]

Update of bug #52517 (project groff):

                  Status:                    None => In Progress            
             Assigned to:                    None => gbranden               
                 Summary: src: adjustments of a line can break down if it
contains "\~" => adjustment can cause overwritten text on lines using \~

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Follow-up Comment #1:

Affects groff 1.22.4.

Here's a nonce patch.  What I really want to do is examine each caller of
`distribute_space()` and see if we're checking our invariants properly in
those places.

For clarity of the change proper, this patch doesn't alter indentation.


diff --git a/src/roff/troff/env.cpp b/src/roff/troff/env.cpp
index 9f00284c6..be07a740c 100644
--- a/src/roff/troff/env.cpp
+++ b/src/roff/troff/env.cpp
@@ -2081,6 +2081,7 @@ static node *node_list_reverse(node *n)
 static void distribute_space(node *n, int nspaces, hunits desired_space,
                             bool force_reverse_node_list = false)
 {
+  assert(desired_space >= H0);
   if (desired_space.is_zero() || nspaces == 0)
     return;
   // Positive desired space is the typical case.  Negative desired space
@@ -2136,6 +2137,11 @@ void environment::possibly_break_line(int start_here,
int forced)
     bp->nd->split(bp->index, &pre, &post);
     *ndp = post;
     hunits extra_space_width = H0;
+    if (target_text_length - bp->width < 0)
+      output_warning(WARN_BREAK, "cannot break before exceeding line"
+         " length");
+    else {
+    extra_space_width = target_text_length - bp->width;
     switch(adjust_mode) {
     case ADJUST_BOTH:
       if (bp->nspaces != 0)
@@ -2153,6 +2159,7 @@ void environment::possibly_break_line(int start_here,
int forced)
       break;
     }
     distribute_space(pre, bp->nspaces, extra_space_width);
+    }
     hunits output_width = bp->width + extra_space_width;
     // This should become an assert() when we can get reliable width
     // data from CJK glyphs.  See Savannah #44018.


While we're tackling this one, it might be an opportunity to implement
squeezable inter-word space.  See bug #40963.


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