Implement declarative buildsystem support

Remove endless boilerplate to perform the same steps in each
package by just declaring which kind of buildsystem the package uses
using the new BuildSystem: spec tag.

Buildsystem macros are just regular parametric macros which can be invoked
manually from specs too, which should help with reuse and handling
complicated cases.

As such, this will only work for simple and/or "perfect" upstream projects
of course. In reality many/most packages need further tweaking, but this
can now be easily done with the new append/prepend modes of the build
scriptlets, and declaratively passed options to specific sections.

Add automake upstream amhello-1.0.tar.gz as an test-case of a rather
hands-free build with added distro specific doc.

Fixes: rpm-software-management#1087

build/parsePreamble.c

@@ -783,6 +783,20 @@ int addLangTag(rpmSpec spec, Header h, rpmTagVal tag,
     return 0;
 }
 
+static int addBuildOption(rpmSpec spec, const char *sect, const char *opt)
+{
+    rpmRC rc = RPMRC_FAIL;
+    if (*sect == '\0')
+	sect = "conf";
+
+    int sn = getSection(sect);
+    if (sn >= 0) {
+	argvAdd(&(spec->buildopts[sn]), opt);
+	rc = RPMRC_OK;
+    }
+    return rc;
+}
+
 static rpmRC handlePreambleTag(rpmSpec spec, Package pkg, rpmTagVal tag,
 		const char *macro, const char *lang)
 {
@@ -820,6 +834,18 @@ static rpmRC handlePreambleTag(rpmSpec spec, Package pkg, rpmTagVal tag,
 	multiToken = 1;
 
     switch (tag) {
+    case RPMTAG_BUILDSYSTEM:
+	SINGLE_TOKEN_ONLY;
+	if (rpmCharCheck(spec, field,
+			ALLOWED_CHARS_NAME, ALLOWED_FIRSTCHARS_NAME))
+	{
+	    goto exit;
+	}
+	break;
+    case RPMTAG_BUILDOPTION:
+	if (addBuildOption(spec, lang, field))
+	    goto exit;
+	break;
     case RPMTAG_NAME:
 	SINGLE_TOKEN_ONLY;
 	if (rpmCharCheck(spec, field,
@@ -1077,8 +1103,10 @@ static struct PreambleRec_s const preambleList[] = {
     {RPMTAG_BUILDARCHS,		0, 0, 0, LEN_AND_STR("buildarchitectures")},
     {RPMTAG_BUILDARCHS,		0, 0, 0, LEN_AND_STR("buildarch")},
     {RPMTAG_BUILDCONFLICTS,	0, 0, 0, LEN_AND_STR("buildconflicts")},
+    {RPMTAG_BUILDOPTION,	2, 0, 0, LEN_AND_STR("buildoption")},
     {RPMTAG_BUILDPREREQ,	0, 1, 0, LEN_AND_STR("buildprereq")},
     {RPMTAG_BUILDREQUIRES,	0, 0, 0, LEN_AND_STR("buildrequires")},
+    {RPMTAG_BUILDSYSTEM,	0, 0, 1, LEN_AND_STR("buildsystem")},
     {RPMTAG_AUTOREQPROV,	0, 0, 0, LEN_AND_STR("autoreqprov")},
     {RPMTAG_AUTOREQ,		0, 0, 0, LEN_AND_STR("autoreq")},
     {RPMTAG_AUTOPROV,		0, 0, 0, LEN_AND_STR("autoprov")},

build/parseSpec.c

@@ -25,6 +25,8 @@
 #define ISMACRO(s,m,len) (rstreqn((s), (m), len) && !risalpha((s)[len]))
 #define ISMACROWITHARG(s,m,len) (rstreqn((s), (m), len) && (risblank((s)[len]) || !(s)[len]))
 
+static rpmRC parseSpecParts(rpmSpec spec, const char *pattern);
+
 typedef struct OpenFileInfo {
     char * fileName;
     FILE *fp;
@@ -894,6 +896,103 @@ static int parseEmpty(rpmSpec spec, int prevParsePart)
     return res;
 }
 
+struct sectname_s {
+    const char *name;
+    int section;
+};
+
+struct sectname_s sectList[] = {
+    { "prep", SECT_PREP },
+    { "conf", SECT_CONF },
+    { "generate_buildrequires", SECT_BUILDREQUIRES },
+    { "build", SECT_BUILD },
+    { "install", SECT_INSTALL },
+    { "check", SECT_CHECK },
+    { "clean", SECT_CLEAN },
+    { NULL, -1 }
+};
+
+int getSection(const char *name)
+{
+    int sn = -1;
+    for (struct sectname_s *sc = sectList; sc->name; sc++) {
+	if (rstreq(name, sc->name)) {
+	    sn = sc->section;
+	    break;
+	}
+    }
+    return sn;
+}
+
+static rpmRC parseBuildsysSect(rpmSpec spec, const char *prefix,
+				struct sectname_s *sc, FD_t fd)
+{
+    rpmRC rc = RPMRC_OK;
+
+    if (spec->sections[sc->section] == NULL) {
+	char *mn = rstrscat(NULL, "buildsystem_", prefix, "_", sc->name, NULL);
+	if (rpmMacroIsParametric(NULL, mn)) {
+	    char *args = NULL;
+	    if (spec->buildopts[sc->section]) {
+		ARGV_t av = NULL;
+		argvAdd(&av, "--");
+		argvAppend(&av, spec->buildopts[sc->section]);
+		args = argvJoin(av, " ");
+		free(av);
+	    }
+	    char *buf = rstrscat(NULL, "%", sc->name, "\n",
+				       "%", mn, " ",
+				       args ? args : "",
+				       "\n", NULL);
+	    size_t blen = strlen(buf);
+	    if (Fwrite(buf, blen, 1, fd) < blen) {
+		rc = RPMRC_FAIL;
+		rpmlog(RPMLOG_ERR,
+			    _("failed to write buildsystem %s %%%s: %s\n"),
+			    prefix, sc->name, strerror(errno));
+	    }
+	    free(buf);
+	    free(args);
+	}
+	free(mn);
+    }
+    return rc;
+}
+
+static rpmRC parseBuildsystem(rpmSpec spec)
+{
+    rpmRC rc = RPMRC_OK;
+    char *buildsystem = rpmExpand("%{?buildsystem}", NULL);
+    if (*buildsystem) {
+	char *path = NULL;
+
+	FD_t fd = rpmMkTempFile(NULL, &path);
+	if (fd == NULL) {
+	    rpmlog(RPMLOG_ERR,
+		_("failed to create temp file for buildsystem: %s\n"),
+		strerror(errno));
+	    rc = RPMRC_FAIL;
+	    goto exit;
+	}
+
+	for (struct sectname_s *sc = sectList; !rc && sc->name; sc++) {
+	    rc = parseBuildsysSect(spec, buildsystem, sc, fd);
+	    if (!rc && spec->sections[sc->section] == NULL)
+		rc = parseBuildsysSect(spec, "default", sc, fd);
+	}
+
+	if (!rc)
+	    rc = parseSpecParts(spec, path);
+	if (!rc)
+	    unlink(path);
+	Fclose(fd);
+    }
+
+exit:
+    free(buildsystem);
+    return rc;
+}
+
 static rpmSpec parseSpec(const char *specFile, rpmSpecFlags flags,
 			 const char *buildRoot, int recursing);
 
@@ -1061,6 +1160,9 @@ static rpmRC parseSpecSection(rpmSpec *specptr, int secondary)
 	}
     }
 
+    if (!secondary && parseBuildsystem(spec))
+	goto errxit;
+
     /* Add arch for each package */
     addArch(spec);
 

build/rpmbuild_internal.h

@@ -150,6 +150,8 @@ struct rpmSpec_s {
     rpmstrPool pool;
 
     StringBuf sections[NR_SECT]; /*!< spec sections (%prep etc) */
+    ARGV_t buildopts[NR_SECT];	/*!< per-section buildsystem options */
+
     StringBuf parsed;		/*!< parsed spec contents */
 
     Package packages;		/*!< Package list. */
@@ -639,6 +641,10 @@ void doSetupMacro(rpmMacroBuf mb, rpmMacroEntry me, ARGV_t margs, size_t *parsed
 RPM_GNUC_INTERNAL
 void doPatchMacro(rpmMacroBuf mb, rpmMacroEntry me, ARGV_t margs, size_t *parsed);
 
+/* Return section number, -1 on error */
+RPM_GNUC_INTERNAL
+int getSection(const char *name);
+
 #ifdef __cplusplus
 }
 #endif

docs/manual/buildsystem.md

@@ -0,0 +1,115 @@
+---
+layout: default
+title: rpm.org - Declarative builds
+---
+
+# Declarative builds
+
+Most software follows common patterns as to how it should be prepared and
+built, such as the classic `./configure && make && make install` case.
+In a spec, these all go to their own sections and when combined with
+the steps to unpack sources, it creates a lot of boilerplate that is
+practically identical across a lot of specs. With the odd tweak to
+this or that detail for distro preferences and the like. To reduce
+the repetitive boilerplate, rpm >= 4.20 adds support for a declarative
+build system mechanism where these common steps can be defined centrally
+per each build system. Packagers then only need to declare which build
+system they use, and optionally supply additional switches and/or
+arguments for the steps where needed.
+
+## Spec usage
+
+In the most simple case, a spec will have an buildsystem declaration such
+as `BuildSystem: cmake` and no manually specified build scripts at all.
+However it's common to have to manually tweak a thing or two. There are
+several ways how to accomplish this, what's appropriate depends on the
+case.
+
+1) Use append and/or prepend as necessary. Need to delete a file after
+the install step? Add a `%install -a` section with the appropriate `rm`.
+Need to `sed` something just before the build step? Add a `%build -p`
+section with the necessary steps.
+
+2) Another very common need is to pass extra arguments to the build
+commands, build configuration in particular. This is done with the
+BuildOption tag, which can appear arbitrary number of times
+in the spec for each section.
+
+```
+BuildOption(<section>): <option string>
+```
+
+without the parenthesis defaults to configuration. In other words,
+these two lines are exactly equivalent:
+
+```
+BuildOption: --enable-fu
+BuildOption(conf): --enable-fu
+```
+
+Passing these per-section options to the actual buildsystem of the
+package is the responsibility of the buildsystem specific macros.
+
+3) Complex packages can have things like multiple build systems, in
+which case you might want to invoke the macros manually, eg.
+
+```
+%buildsystem_autotools_build
+cd python
+%buildsystem_python_build
+```
+
+## Supporting new build systems
+
+Supporting new build system types is just a matter of declaring a few
+macros for the build scriptlet sections relevant to the build system.
+
+Scriptlet                 | Mandatory | Buildsystem macro
+-------------------------------------------
+`%prep`                   | No        | `%buildsystem_name_prep`
+`%conf`                   | Yes       | `%buildsystem_name_conf`
+`%generate_buildrequires` | No        | `%buildsystem_name_generate_buildrequires`
+`%build`                  | Yes       | `%buildsystem_name_build`
+`%install`                | Yes       | `%buildsystem_name_install`
+`%check`                  | No        | `%buildsystem_name_check`
+`%clean`                  | No        | `%buildsystem_name_clean`
+
+Replace "name" with the buildsystem name, eg `%buildsystem_cmake_build`.
+When BuildSystem: tag is set, these automatically populate the corresponding
+spec section, unless the spec manually overrides it. All buildsystem
+macros are required to be parametric to have enforceable semantics.
+
+For example, supporting the classic autotools case could be built on top
+of existing helper macros:
+```
+%buildsystem_autotools_conf() %configure %*
+%buildsystem_autotools_build() %make_build %*
+%buildsystem_autotools_install() %make_install %*
+```
+
+## Global defaults
+
+While the actual steps to build and install obviously differ greatly among
+different buildsystems, they still typically share a lot of common steps.
+Namely, unpacking sources, applying patches and cleaning up at the end.
+To avoid each buildsystem having to declare a `%prep` to automatically
+perform the same common duties, with inevitable subtle differences and
+bugs, rpm additionally supports global default actions for all scriptlets
+supported by the buildsystem mechanism. These defaults, if defined,
+are only called if there's no corresponding buildsystem specific macro
+defined.
+
+Rpm ships with a default to perform `%autosetup -p1` in `%prep`,
+so unless a buildsystem has an unusual source preparation sequence
+source preparation will "just work". Passing extra arguments to a section
+is exactly the same with defaults and buildsystem specific macros, so
+the user does not need to know which one is being used. For example,
+if the upstream source doesn' version their source release directory,
+it can simply be supplied with the following in the spec:
+
+```
+BuildOption(prep): -n %{name}
+```
+
+Note that the defaults are only meant for upstream and distro-level
+customization only, do not override them for your own purposes!

docs/manual/index.md

@@ -18,6 +18,7 @@ title: rpm.org - RPM Reference Manual
 ## Package Building
 * [Build Process](buildprocess.md)
 * [Spec Syntax](spec.md)
+  * [Autobuild](autobuild.md)
   * [Autosetup](autosetup.md)
   * Dependencies
     * [Dependencies Basics](dependencies.md)

docs/manual/spec.md

@@ -206,6 +206,12 @@ with old packages that might still depend on it.
 
 Do not use in new packages.
 
+#### Buildsystem
+
+Automatically populate the spec build scripts for the given build system,
+such as `Buildsystem: autotools". See [declarative build](buildsystem.md)
+documentation for more details.
+
 #### AutoReqProv
 #### AutoReq
 #### AutoProv

include/rpm/rpmtag.h

@@ -386,6 +386,8 @@ typedef enum rpmTag_e {
     RPMTAG_PREUNTRANSFLAGS	= 5107, /* i */
     RPMTAG_POSTUNTRANSFLAGS	= 5108, /* i */
     RPMTAG_SYSUSERS		= 5109, /* s[] extension */
+    RPMTAG_BUILDSYSTEM		= 5110, /* internal */
+    RPMTAG_BUILDOPTION		= 5111, /* internal */
 
     RPMTAG_FIRSTFREE_TAG	/*!< internal */
 } rpmTag;

macros.in

@@ -1352,5 +1352,19 @@ end
     end
 }
 
+# Global buildsystem defaults
+%buildsystem_default_prep() %autosetup -p1 %*
+
+# Example buildsystem for autotools
+%buildsystem_autotools_conf() %configure %*
+%buildsystem_autotools_build() %make_build %*
+%buildsystem_autotools_install() %make_install %*
+
+# Example buildsystem for cmake
+%buildsystem_cmake_conf() cmake %* -B __rpmbuild -S .
+%buildsystem_cmake_build() cmake --build __rpmbuild %{?smp_mflags} %{?verbose:-v} -- %*
+%buildsystem_cmake_install() DESTDIR=${RPM_BUILD_ROOT} cmake --install __rpmbuild %{?verbose:-v} %*
+
 # \endverbatim
 #*/
+

tests/data/SPECS/amhello.spec

@@ -0,0 +1,34 @@
+%bcond_with alt
+
+Name: amhello
+Version: 1.0
+Source: amhello-%{version}.tar.gz
+License: GPLv2
+Summary: Autotools example
+BuildSystem: autotools
+
+%if %{with alt}
+BuildOption: --program-prefix=alt-
+BuildOption(install): DESTDIR=${RPM_BUILD_ROOT}/alt
+Release: 1alt
+%else
+Release: 1
+%endif
+
+%description
+%{summary}
+
+%build -a
+cat << EOF > README.distro
+Add some distro specific notes.
+EOF
+
+%files
+%doc README.distro
+%if %{with alt}
+/alt/%{_bindir}/alt-hello
+/alt/%{_docdir}/%{name}
+%else
+%{_bindir}/hello
+%{_docdir}/%{name}
+%endif