make: handling of leading whitespace in makefiles

Try to match how different makes handle leading whitespace in
makefiles.  (Tested with GNU, BSD, Schily and UNIX Version 7
make.)

- Commands in rules must start with a tab.  It's the law.

- BSD make doesn't allow any whitespace at the start of an include
  line.  Enforce this restriction in POSIX mode: 'the word include
  ... appears at the beginning of a line'.  As an extension allow
  arbitrary tabs or spaces.

- All implementations allow a space as the first character of a
  macro definition or rule.  Permit this in all cases.

- Only GNU make allows a tab as the first character of a macro
  definition, but POSIX 2024 seems to permit it too: 'string1 is
  defined as all characters from the first non-<blank> character to
  the last non-<blank> character, inclusive'.  Allow this in POSIX
  2024 mode and as an extension.

- No implementation allows a tab as the first character of a rule.
  Disallow this in all cases.

Adds 32-64 bytes.

(pdpmake GitHub issue 63)

1 files changed, 16 insertions, 14 deletions

diff --git a/miscutils/make.c b/miscutils/make.c
index b2edfdbb4..1e7b77ddb 100644
--- a/miscutils/make.c
+++ b/miscutils/make.c
@@ -1478,15 +1478,10 @@ expand_macros(const char *str, int except_dollar)
 /*
  * Process a non-command line
  */
-static char *
+static void
 process_line(char *s)
 {
-        char *r, *t;
-
-        // Skip leading blanks
-        while (isblank(*s))
-                s++;
-        r = s;
+        char *t;
 
         // Strip comment
         // don't treat '#' in macro expansion as a comment
@@ -1519,8 +1514,6 @@ process_line(char *s)
                 }
         }
         *t = '\0';
-
-        return r;
 }
 
 enum {
@@ -1605,8 +1598,8 @@ skip_line(const char *str1)
         int ret = cstate[clevel] & SKIP_LINE;
         int key;
 
-        copy = xstrdup(str1);
-        q = process_line(copy);
+        q = copy = xstrdup(str1);
+        process_line(copy);
         if ((token = gettok(&q)) != NULL) {
                 switch (index_in_strings("else\0endif\0", token)) {
                 case ENDIF:
@@ -2055,8 +2048,6 @@ input(FILE *fd, int ilevel)
         str1 = readline(fd, FALSE);
         while (str1) {
                 str2 = NULL;
-                if (*str1 == '\t')      // Command without target
-                        error("command not allowed here");
 
                 // Newlines and comments are handled differently in command lines
                 // and other types of line.  Take a copy of the current line before
@@ -2066,9 +2057,13 @@ input(FILE *fd, int ilevel)
                 //   target: prereq; command
                 //
                 copy = xstrdup(str1);
-                str = process_line(str1);
+                process_line(str1);
+                str = str1;
 
                 // Check for an include line
+                if (!posix)
+                        while (isblank(*str))
+                                ++str;
                 minus = !POSIX_2017 && *str == '-';
                 p = str + minus;
                 if (strncmp(p, "include", 7) == 0 && isblank(p[7])) {
@@ -2117,6 +2112,11 @@ input(FILE *fd, int ilevel)
                 }
 
                 // Check for a macro definition
+                str = str1;
+                // POSIX 2024 seems to allow a tab as the first character of
+                // a macro definition, though most implementations don't.
+                if (POSIX_2017 && *str == '\t')
+                        error("command not allowed here");
                 if (find_char(str, '=') != NULL) {
                         int level = (useenv || fd == NULL) ? 4 : 3;
                         // Use a copy of the line:  we might need the original
@@ -2221,6 +2221,8 @@ input(FILE *fd, int ilevel)
 
                 // If we get here it must be a target rule
  try_target:
+                if (*str == '\t')       // Command without target
+                        error("command not allowed here");
                 p = expanded = expand_macros(str, FALSE);
 
                 // Look for colon separator