vim-patch:8.2.4934: string interpolation fails when not evaluating

Problem:    String interpolation fails when not evaluating.
Solution:   Skip the expression when not evaluating. (closes vim/vim#10398)

https://github.com/vim/vim/commit/70c41241c2701f26a99085e433925a206ca265a3

Co-authored-by: Bram Moolenaar <Bram@vim.org>

4 files changed, 15 insertions, 16 deletions

diff --git a/runtime/syntax/modula3.vim b/runtime/syntax/modula3.vim
index 390a1a90ff..67243db600 100644
--- a/runtime/syntax/modula3.vim
+++ b/runtime/syntax/modula3.vim
@@ -84,9 +84,7 @@ syn case ignore
 
   let s:digits = "0123456789ABCDEF"
   for s:radix in range(2, 16)
-    " Nvim does not support interpolated strings yet.
-    " exe $'syn match modula3Integer "\<{s:radix}_[{s:digits[:s:radix - 1]}]\+L\=\>"'
-    exe 'syn match modula3Integer "\<' .. s:radix .. '_[' .. s:digits[:s:radix - 1] .. ']\+L\=\>"'
+    exe $'syn match modula3Integer "\<{s:radix}_[{s:digits[:s:radix - 1]}]\+L\=\>"'
   endfor
   unlet s:digits s:radix
 
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index da345e4b53..289489a182 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -4140,7 +4140,7 @@ int eval_interp_string(char **arg, typval_T *rettv, bool evaluate)
       (*arg)++;
       break;
     }
-    char *p = eval_one_expr_in_str(*arg, &ga);
+    char *p = eval_one_expr_in_str(*arg, &ga, evaluate);
     if (p == NULL) {
       ret = FAIL;
       break;
diff --git a/src/nvim/eval/vars.c b/src/nvim/eval/vars.c
index 7ae7b5a57a..d3ca2624eb 100644
--- a/src/nvim/eval/vars.c
+++ b/src/nvim/eval/vars.c
@@ -55,8 +55,9 @@ static const char *e_lock_unlock = N_("E940: Cannot lock or unlock variable %s")
 
 /// Evaluate one Vim expression {expr} in string "p" and append the
 /// resulting string to "gap".  "p" points to the opening "{".
+/// When "evaluate" is false only skip over the expression.
 /// Return a pointer to the character after "}", NULL for an error.
-char *eval_one_expr_in_str(char *p, garray_T *gap)
+char *eval_one_expr_in_str(char *p, garray_T *gap, bool evaluate)
 {
   char *block_start = skipwhite(p + 1);  // skip the opening {
   char *block_end = block_start;
@@ -73,14 +74,16 @@ char *eval_one_expr_in_str(char *p, garray_T *gap)
     semsg(_(e_missing_close_curly_str), p);
     return NULL;
   }
-  *block_end = NUL;
-  char *expr_val = eval_to_string(block_start, true);
-  *block_end = '}';
-  if (expr_val == NULL) {
-    return NULL;
+  if (evaluate) {
+    *block_end = NUL;
+    char *expr_val = eval_to_string(block_start, true);
+    *block_end = '}';
+    if (expr_val == NULL) {
+      return NULL;
+    }
+    ga_concat(gap, expr_val);
+    xfree(expr_val);
   }
-  ga_concat(gap, expr_val);
-  xfree(expr_val);
 
   return block_end + 1;
 }
@@ -129,7 +132,7 @@ char *eval_all_expr_in_str(char *str)
     }
 
     // Evaluate the expression and append the result.
-    p = eval_one_expr_in_str(p, &ga);
+    p = eval_one_expr_in_str(p, &ga, true);
     if (p == NULL) {
       ga_clear(&ga);
       return NULL;
diff --git a/test/old/testdir/test_scriptnames.vim b/test/old/testdir/test_scriptnames.vim
index d804684722..06ae305ab7 100644
--- a/test/old/testdir/test_scriptnames.vim
+++ b/test/old/testdir/test_scriptnames.vim
@@ -35,9 +35,7 @@ func Test_getscriptinfo()
   source Xscript
   let l = getscriptinfo()
   call assert_match('Xscript$', l[-1].name)
-  " Nvim does not support interpolated strings yet.
-  " call assert_equal(g:loaded_script_id, $"<SNR>{l[-1].sid}_")
-  call assert_equal(g:loaded_script_id, '<SNR>' . l[-1].sid . '_')
+  call assert_equal(g:loaded_script_id, $"<SNR>{l[-1].sid}_")
   call delete('Xscript')
 endfunc