mamake: add nice PS4 to shell actions, demystifying log output

The shell action trace in the log file has always been hard to
follow. Shell action commands are traced without any context. For
people unfamiliar with the build system (currently everyone but a
handful of people), it is unclear where these come from.

mamake now sets a PS4 tracing prompt for each shell action that
shows the Mamfile that the shell action originates from as well as
the line number range of the corresponding make...done block.

It would be nice if we could trace the exact line number of each
'exec' statement, but that is not possible with the basic design of
this system; 'exec' statements are combined into a script buffer
and that is executed as a whole upon reaching 'done'. Since 'exec'
statements can begin at any point in the block and need not even be
contiguous to belong to the same script, exact line number
information is lost.

However, showing the make...done block range also has advantages;
it makes it more intuitive to understand the build system. Here is
a sample fragment:

+ (libast/Mamfile:239-242) /bin/cp -f FEATURE/sys ast_sys.h
+ (libast/Mamfile:158-250) iffe -v -X ast -X std -c 'cc  -D_BL[...]
iffe: test results in FEATURE/stdio are up to date
+ (libast/Mamfile:157-254) /bin/cp -f FEATURE/stdio ast_stdio.h

Note how the line number ranges show three different shell scripts
belonging to three nested blocks.

src/cmd/INIT/mamake.c:
- Add a 'line' member to the Rule_t struct.
- rule(): When defining a rule r (e.g. upon 'make'), store the
  current line number in r->line.
- run(): When running a shell action, emit a PS4 assignment set a
  nice PS4 showing the last component of the parent directory and
  the current file name (generally Mamfile), r->line (the 'make'
  line), and the current line (the 'done' line).

src/cmd/INIT/mamake.c

@@ -238,6 +238,7 @@ typedef struct Rule_s			/* rule item			*/
 	int		flags;		/* RULE_* flags			*/
 	int		making;		/* currently make()ing		*/
 	unsigned long	time;		/* modification time		*/
+	unsigned long	line;		/* starting line in Mamfile	*/
 } Rule_t;
 
 typedef struct Stream_s			/* input file stream stack	*/
@@ -651,6 +652,7 @@ rule(char* name)
 		if (!(r = newof(0, Rule_t, 1, 0)))
 			report(3, "out of memory [rule]", name, 0);
 		r->name = (char*)search(state.rules, name, r);
+		r->line = state.sp ? state.sp->line : 0;
 	}
 	return r;
 }
@@ -1274,7 +1276,25 @@ run(Rule_t* r, char* s)
 		);
 		/* show trace for the shell action commands */
 		if (!(r->flags & RULE_notrace))
-			append(buf,"set -x\n");
+		{
+			char *cp;
+			/* construct a nice PS4 */
+			append(buf,"PS4='+ (");
+			cp = state.pwd + strlen(state.pwd) - 1;
+			while (*cp != '/' && *cp != '\'' && cp > state.pwd)
+				cp--;
+			append(buf, cp + 1);
+			add(buf, '/');
+			append(buf, state.file);
+			if (r->line && state.sp)
+			{
+				char nbuf[64];
+				sprintf(nbuf, ":%lu-%lu", r->line, state.sp->line);
+				append(buf, nbuf);
+			}
+			append(buf,") '\n"
+				"set -x\n");
+		}
 	}
 	if (state.view)
 	{

src/lib/libast/Mamfile

@@ -117,11 +117,11 @@ make install virtual
 										exec - iffe ${IFFEFLAGS} -v -X ast -X std -c "${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I.  ${LDFLAGS}" run features/map.c
 									done
 									exec - ${STDCP} -f FEATURE/map ast_map.h
-								done
-							done
-						done
-					done
-				done
+								done ast_map.h
+							done ast_common.h
+						done std/bytesex.h
+					done std/endian.h
+				done FEATURE/param
 				make FEATURE/aso
 					prev features/aso
 					exec - iffe ${IFFEFLAGS} -v -X ast -X std -c "${CC} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS}" run features/aso
@@ -149,11 +149,11 @@ make install virtual
 							prev FEATURE/common
 							prev FEATURE/lib
 							prev FEATURE/standards
-						done
+						done features/limits.c
 						exec - iffe ${IFFEFLAGS} -v -X ast -X std -c "${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I. -Icomp -Iinclude -Istd  ${LDFLAGS}" run features/limits.c
-					done
+					done FEATURE/limits
 					exec - ${STDCP} -f FEATURE/limits ast_limits.h
-				done
+				done ast_limits.h
 				make ast_stdio.h dontcare
 					make FEATURE/stdio
 						prev features/stdio
@@ -246,12 +246,12 @@ make install virtual
 							done
 							prev ast_common.h
 							prev ast_standards.h
-						done
-					done
+						done include/ast_std.h
+					done FEATURE/stdio
 					exec - ${STDCP} -f FEATURE/stdio ast_stdio.h
 					prev include/sfio_s.h
 					prev include/ast_std.h
-				done
+				done ast_stdio.h
 				make ast_nl_types.h
 					make FEATURE/nl_types
 						prev features/nl_types
@@ -302,7 +302,7 @@ make install virtual
 				exec - 0)	echo ' -lm' >> ast.req ;;
 				exec - *)	touch ast.req ;;
 				exec - esac
-			done
+			done ast.req
 			make state.o
 				make misc/state.c
 					make include/ast.h implicit