Implement perfect dependency rebuilding

This means, if foo depends on blah, which in turn depends on blub and
blub changes, blah get's rebuild but stays the same then foo won't be
rebuild as it's dependencies (blah) have not changed.

Note that because our currently included sha1 implementation does not
work correctly, this doesn't either if the changes are small.

1 files changed, 62 insertions, 64 deletions

diff --git a/src/build.c b/src/build.c
index 18ead3f..677f7b9 100644
--- a/src/build.c
+++ b/src/build.c
@@ -36,7 +36,7 @@ static char **parse_shebang(char *target, char *dofile, char *temp_output);
 static char **parsecmd(char *cmd, size_t *i, size_t keep_free);
 static char *get_relpath(const char *target);
 static char *get_dep_path(const char *target);
-static void write_dep_hash(const char *target);
+static int write_dep_hash(const char *target, unsigned char *old_hash);
 static int handle_c(const char *target);
 
 struct do_attr {
@@ -48,15 +48,16 @@ struct do_attr {
 
 /* Build given target, using it's do-file. */
 int build_target(const char *target) {
+	int retval = 1;
 	/* get the do-file which we are going to execute */
 	struct do_attr *dofiles = get_dofiles(target);
 	if (!dofiles->chosen) {
 		if (fexists(target)) {
 			/* if our target file has no do file associated but exists,
 			   then we treat it as a source */
-			write_dep_hash(target);
+			write_dep_hash(target, NULL);
 			free_do_attr(dofiles);
-			return 1;
+			return retval;
 		}
 
 		die("%s couldn't be built as no suitable do-file exists\n", target);
@@ -66,8 +67,23 @@ int build_target(const char *target) {
 	printf("redo  %s\n", reltarget);
 	free(reltarget);
 
-	/* remove old dependency file */
+	/* get the old hash (if any) */
+	unsigned char old_hash[HASHSIZE];
 	char *dep_file = get_dep_path(target);
+	FILE *fp = fopen(dep_file, "rb");
+	if (!fp) {
+		if (errno != ENOENT)
+			fatal("redo: failed to open %s\n", dep_file);
+		memset(old_hash, 0, HASHSIZE); // FIXME
+	} else {
+		if (!fseek(fp, sizeof(unsigned), SEEK_SET))
+			fatal("redo: fseek() failed");
+		if (fread(old_hash, 1, HASHSIZE, fp) < HASHSIZE)
+			fatal("redo: failed to read stuff");
+		fclose(fp);
+	}
+
+	/* remove old dependency file */
 	if (remove(dep_file))
 		if (errno != ENOENT)
 			fatal("redo: failed to remove %s", dep_file);
@@ -118,26 +134,32 @@ int build_target(const char *target) {
 		fatal("waitpid() failed: ");
 	bool remove_temp = true;
 
+	/* check how our child exited */
 	if (WIFEXITED(status)) {
-		if (WEXITSTATUS(status)) {
+		if (WEXITSTATUS(status))
 			die("redo: invoked do-file %s failed: %d\n", dofiles->chosen,
 			    WEXITSTATUS(status));
-		} else {
-			/* successful */
-
-			/* if the file is 0 bytes long we delete it */
-			if (fsize(temp_output) > 0)
-				remove_temp = false;
-		}
 	} else {
 		/* something very wrong happened with the child */
 		die("redo: invoked do-file did not terminate correctly\n");
 	}
 
+	/* check if our output file is > 0 bytes long */
+	if (fsize(temp_output) > 0) {
+		if (rename(temp_output, target))
+			fatal("redo: failed to rename %s to %s", temp_output, target);
+
+		retval = write_dep_hash(target, old_hash);
+	} else {
+		if (remove(temp_output))
+			if (errno != ENOENT)
+				fatal("redo: failed to remove %s", temp_output);
+	}
+
 	/* depend on the do-file */
 	char *temp = get_dep_path(dofiles->chosen);
 	if (!fexists(temp))
-		write_dep_hash(dofiles->chosen);
+		write_dep_hash(dofiles->chosen, NULL);
 
 	free(temp);
 	add_dep(dofiles->chosen, target, 'c');
@@ -146,21 +168,10 @@ int build_target(const char *target) {
 	if (dofiles->general == dofiles->chosen)
 		add_dep(dofiles->specific, target, 'e');
 
-	if (remove_temp) {
-		if (remove(temp_output))
-			if (errno != ENOENT)
-				fatal("redo: failed to remove %s", temp_output);
-	} else {
-		if (rename(temp_output, target))
-			fatal("redo: failed to rename %s to %s", temp_output, target);
-
-		write_dep_hash(target);
-	}
-
 	free(temp_output);
 	free_do_attr(dofiles);
 
-	return 1;
+	return retval;
 }
 
 /* Read and parse shebang and return an argv-like pointer array containing the
@@ -257,7 +268,6 @@ static struct do_attr *get_dofiles(const char *target) {
 
 	return dofiles;
 }
-
 /* Free the do_attr struct. */
 static void free_do_attr(struct do_attr *thing) {
 	free(thing->specific);
@@ -363,14 +373,16 @@ static void hash_file(const char *target, unsigned char *hash) {
 	fclose(in);
 }
 
-/* Calculate and store the hash of target in the right dependency file. */
-static void write_dep_hash(const char *target) {
+/* Calculate and store the hash of target in the right dependency file. Returns
+   a nonzero value if the hash changed or zero otherwise. */
+static int write_dep_hash(const char *target, unsigned char *old_hash) {
 	unsigned char hash[HASHSIZE];
 	unsigned magic = atoi(getenv("REDO_MAGIC"));
 
 	hash_file(target, hash);
 
 	char *dep_path = get_dep_path(target);
+
 	int out = open(dep_path, O_WRONLY | O_CREAT, 0644);
 	if (out < 0)
 		fatal("redo: failed to open %s", dep_path);
@@ -383,22 +395,24 @@ static void write_dep_hash(const char *target) {
 
 	if (close(out))
 		fatal("redo: failed to close %s", dep_path);
+
 	free(dep_path);
+
+	if (old_hash)
+		return memcmp(hash, old_hash, HASHSIZE);
+	else
+		return 1;
+
 }
 
 int update_target(const char *target, int ident) {
 	switch(ident) {
 	case 'a':
-		debug("%s is not up-to-date: always rebuild\n", target);
-		build_target(target);
-		return 1;
+		return build_target(target);
 	case 'e':
-		if (fexists(target)) {
-			debug("%s is not up-to-date: target exist and e ident was chosen\n",
-			      target);
-			build_target(target);
-			return 1;
-		}
+		if (fexists(target))
+			return build_target(target);
+
 		return 0;
 	case 'c':
 		return handle_c(target);
@@ -408,12 +422,8 @@ int update_target(const char *target, int ident) {
 }
 
 static int handle_c(const char *target) {
-	if (!fexists(target)) {
-		/* target does not exist */
-		debug("%s is not up-to-date: target doesn't exist\n", target);
-		build_target(target);
-		return 1;
-	}
+	if (!fexists(target))
+		return build_target(target);
 
 	char *dep_path = get_dep_path(target);
 
@@ -421,11 +431,8 @@ static int handle_c(const char *target) {
 	if (!fp) {
 		if (errno == ENOENT) {
 			/* dependency file does not exist */
-			debug("%s is not up-to-date: dependency file (%s) doesn't exist\n",
-			      target, dep_path);
-			build_target(target);
 			free(dep_path);
-			return 1;
+			return build_target(target);
 		} else {
 			fatal("redo: failed to open %s", dep_path);
 		}
@@ -446,11 +453,8 @@ static int handle_c(const char *target) {
 	bool rebuild = false;
 	unsigned char hash[HASHSIZE];
 	hash_file(target, hash);
-	if (memcmp(hash, buf+sizeof(unsigned), HASHSIZE)) {
-		debug("%s is not-up-to-date: hashes don't match\n", target);
-		build_target(target);
-		return 1;
-	}
+	if (memcmp(hash, buf+sizeof(unsigned), HASHSIZE))
+		return build_target(target);
 
 	char *ptr;
 
@@ -468,18 +472,13 @@ static int handle_c(const char *target) {
 				/* if our path is relative we need to prefix it with the
 				   root project directory or the path will be invalid */
 				char *abs = concat(3, root, "/", &ptr[1]);
-				if (update_target(abs, ptr[0])) {
-					debug("%s is not up-to-date: subdependency %s is out-of-date\n",
-						  target, abs);
+				if (update_target(abs, ptr[0]))
 					rebuild = true;
-				}
+
 				free(abs);
 			} else {
-				if (update_target(&ptr[1], ptr[0])) {
-					debug("%s is not up-to-date: subdependency %s is out-of-date\n",
-						  target, &ptr[1]);
+				if (update_target(&ptr[1], ptr[0]))
 					rebuild = true;
-				}
 			}
 			ptr = &buf[i+1];
 		}
@@ -493,9 +492,8 @@ static int handle_c(const char *target) {
 	}
 
 	fclose(fp);
-	if (rebuild) {
-		build_target(target);
-		return 1;
-	}
+	if (rebuild)
+		return build_target(target);
+
 	return 0;
 }