ash: parser: Fix handling of empty aliases

Upstream commit:

    Date: Tue, 28 Apr 2020 01:15:26 +1000
    parser: Fix handling of empty aliases

    Dash was incorrectly handling empty aliases. When attempting to use an
    empty alias with nothing else, I'm (incorrectly) prompted for more
    input:

    ```
    $ alias empty=''
    $ empty
    >
    ```

    Other shells (e.g., bash, yash) correctly handle the lone, empty alias as an
    empty command:

    ```
    $ alias empty=''
    $ empty
    $
    ```

    The problem here is that we incorrectly enter the loop eating TNLs
    in readtoken().  This patch fixes it by setting checkkwd correctly.

function                                             old     new   delta
list                                                 351     355      +4

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 15 insertions, 21 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 35dbb2f28..5a18ff1a1 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -11755,27 +11755,28 @@ static union node *andor(void);
 static union node *pipeline(void);
 static union node *parse_command(void);
 static void parseheredoc(void);
-static int peektoken(void);
 static int readtoken(void);
 
 static union node *
 list(int nlflag)
 {
+        int chknl = nlflag & 1 ? 0 : CHKNL;
         union node *n1, *n2, *n3;
         int tok;
 
         n1 = NULL;
         for (;;) {
-                switch (readtoken()) {
+                checkkwd = chknl | CHKKWD | CHKALIAS;
+                tok = readtoken();
+                switch (tok) {
                 case TNL:
-                        if (!(nlflag & 1))
-                                break;
                         parseheredoc();
                         return n1;
 
                 case TEOF:
-                        if (!n1 && (nlflag & 1))
+                        if (!n1 && !chknl)
                                 n1 = NODE_EOF;
+ out_eof:
                         parseheredoc();
                         tokpushback++;
                         lasttoken = TEOF;
@@ -11783,8 +11784,7 @@ list(int nlflag)
                 }
 
                 tokpushback++;
-                checkkwd = CHKNL | CHKKWD | CHKALIAS;
-                if (nlflag == 2 && ((1 << peektoken()) & tokendlist))
+                if (nlflag == 2 && ((1 << tok) & tokendlist))
                         return n1;
                 nlflag |= 2;
 
@@ -11813,15 +11813,16 @@ list(int nlflag)
                         n1 = n3;
                 }
                 switch (tok) {
-                case TNL:
                 case TEOF:
+                        goto out_eof;
+                case TNL:
                         tokpushback = 1;
                         /* fall through */
                 case TBACKGND:
                 case TSEMI:
                         break;
                 default:
-                        if ((nlflag & 1))
+                        if (!chknl)
                                 raise_error_unexpected_syntax(-1);
                         tokpushback = 1;
                         return n1;
@@ -11995,8 +11996,9 @@ simplecmd(void)
                 switch (t) {
 #if BASH_FUNCTION
                 case TFUNCTION:
-                        if (peektoken() != TWORD)
+                        if (readtoken() != TWORD)
                                 raise_error_unexpected_syntax(TWORD);
+                        tokpushback = 1;
                         function_flag = 1;
                         break;
 #endif
@@ -12033,7 +12035,9 @@ simplecmd(void)
 #if BASH_FUNCTION
                         if (function_flag) {
                                 checkkwd = CHKNL | CHKKWD;
-                                switch (peektoken()) {
+                                t = readtoken();
+                                tokpushback = 1;
+                                switch (t) {
                                 case TBEGIN:
                                 case TIF:
                                 case TCASE:
@@ -13306,16 +13310,6 @@ readtoken(void)
         return t;
 }
 
-static int
-peektoken(void)
-{
-        int t;
-
-        t = readtoken();
-        tokpushback = 1;
-        return t;
-}
-
 /*
  * Read and parse a command.  Returns NODE_EOF on end of file.
  * (NULL is a valid parse tree indicating a blank line.)