cgo: define CGO_CFLAGS and CGO_LDFLAGS in Go files

R=rsc, binet
CC=golang-dev
https://golang.org/cl/3921043

src/Make.pkg

@@ -48,7 +48,7 @@ coverage:
 	6cov -g $(shell pwd) $O.out | grep -v '_test\.go:'
 
 CLEANFILES+=*.cgo1.go *.cgo2.c _cgo_defun.c _cgo_gotypes.go _cgo_export.*
-CLEANFILES+=_cgo_.c _cgo_import.c _cgo_main.c
+CLEANFILES+=_cgo_.c _cgo_import.c _cgo_main.c _cgo_flags _cgo_run
 CLEANFILES+=*.so _obj _test _testmain.go *.exe
 
 test:
@@ -112,11 +112,21 @@ dir:
 #
 
 ifdef CGOFILES
-_cgo_defun.c: $(CGOFILES)
+_cgo_run: $(CGOFILES)
+	@touch _cgo_run
 	CGOPKGPATH=$(dir) cgo -- $(CGO_CFLAGS) $(CGOFILES)
 
+# _CGO_CFLAGS and _CGO_LDFLAGS are defined via the evaluation of _cgo_flags.
+# The include happens before the commands in the recipe run,
+# so it cannot be done in the same recipe that runs cgo.
+_cgo_flags: _cgo_run
+	$(eval include _cgo_flags)
+
+# Include any previous flags in case cgo files are up to date.
+-include _cgo_flags
+
 # Ugly but necessary - cgo writes these files too.
-_cgo_gotypes.go _cgo_export.c _cgo_export.h _cgo_main.c: _cgo_defun.c
+_cgo_gotypes.go _cgo_export.c _cgo_export.h _cgo_main.c _cgo_defun.c: _cgo_flags
 	@true
 
 %.cgo1.go %.cgo2.c: _cgo_defun.c
@@ -125,7 +135,7 @@ endif
 
 # Compile rules for gcc source files.
 %.o: %.c
-	$(HOST_CC) $(_CGO_CFLAGS_$(GOARCH)) -g -fPIC -O2 -o $@ -c $(CGO_CFLAGS) $*.c
+	$(HOST_CC) $(_CGO_CFLAGS_$(GOARCH)) -g -fPIC -O2 -o $@ -c $(CGO_CFLAGS) $(_CGO_CFLAGS) $*.c
 
 # To find out which symbols are needed from external libraries
 # and which libraries are needed, we build a simple a.out that
@@ -136,10 +146,10 @@ endif
 # by Go code.  That's crosscall2 and any exported symbols.
 
 _cgo_main.o: _cgo_main.c
-	$(HOST_CC) $(_CGO_CFLAGS_$(GOARCH)) -g -fPIC -O2 -o $@ -c $(CGO_CFLAGS) _cgo_main.c
+	$(HOST_CC) $(_CGO_CFLAGS_$(GOARCH)) -g -fPIC -O2 -o $@ -c $(CGO_CFLAGS) $(_CGO_CFLAGS) _cgo_main.c
 
 _cgo1_.o: _cgo_main.o $(CGO_OFILES)
-	$(HOST_CC) $(_CGO_CFLAGS_$(GOARCH)) -g -fPIC -O2 -o $@ $^ $(CGO_LDFLAGS)
+	$(HOST_CC) $(_CGO_CFLAGS_$(GOARCH)) -g -fPIC -O2 -o $@ $^ $(CGO_LDFLAGS) $(_CGO_LDFLAGS)
 
 _cgo_import.c: _cgo1_.o
 	cgo -dynimport _cgo1_.o >_$@ && mv -f _$@ $@

src/cmd/cgo/doc.go

@@ -23,6 +23,15 @@ the package.  For example:
 	// #include <errno.h>
 	import "C"
 
+CFLAGS and LDFLAGS may be defined with pseudo #cgo directives
+within these comments to tweak the behavior of gcc.  Values defined
+in multiple directives are concatenated together.  For example:
+
+	// #cgo CFLAGS: -DPNG_DEBUG=1
+	// #cgo LDFLAGS: -lpng
+	// #include <png.h>
+	import "C"
+
 C identifiers or field names that are keywords in Go can be
 accessed by prefixing them with an underscore: if x points at
 a C struct with a field named "type", x._type accesses the field.

src/cmd/cgo/gcc.go

@@ -21,6 +21,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"unicode"
 )
 
 var debugDefine = flag.Bool("debug-define", false, "print relevant #defines")
@@ -59,6 +60,107 @@ func cname(s string) string {
 	return s
 }
 
+// ParseFlags extracts #cgo CFLAGS and LDFLAGS options from the file
+// preamble. Multiple occurrences are concatenated with a separating space,
+// even across files.
+func (p *Package) ParseFlags(f *File, srcfile string) {
+	linesIn := strings.Split(f.Preamble, "\n", -1)
+	linesOut := make([]string, 0, len(linesIn))
+	for _, line := range linesIn {
+		l := strings.TrimSpace(line)
+		if len(l) < 5 || l[:4] != "#cgo" || !unicode.IsSpace(int(l[4])) {
+			linesOut = append(linesOut, line)
+			continue
+		}
+
+		l = strings.TrimSpace(l[4:])
+		fields := strings.Split(l, ":", 2)
+		if len(fields) != 2 {
+			fatal("%s: bad #cgo line: %s", srcfile, line)
+		}
+
+		k := fields[0]
+		v := strings.TrimSpace(fields[1])
+		if k != "CFLAGS" && k != "LDFLAGS" {
+			fatal("%s: unsupported #cgo option %s", srcfile, k)
+		}
+		args, err := splitQuoted(v)
+		if err != nil {
+			fatal("%s: bad #cgo option %s: %s", srcfile, k, err.String())
+		}
+		if oldv, ok := p.CgoFlags[k]; ok {
+			p.CgoFlags[k] = oldv + " " + v
+		} else {
+			p.CgoFlags[k] = v
+		}
+		if k == "CFLAGS" {
+			p.GccOptions = append(p.GccOptions, args...)
+		}
+	}
+	f.Preamble = strings.Join(linesOut, "\n")
+}
+
+// splitQuoted splits the string s around each instance of one or more consecutive
+// white space characters while taking into account quotes and escaping, and
+// returns an array of substrings of s or an empty list if s contains only white space.
+// Single quotes and double quotes are recognized to prevent splitting within the
+// quoted region, and are removed from the resulting substrings. If a quote in s
+// isn't closed err will be set and r will have the unclosed argument as the
+// last element.  The backslash is used for escaping.
+//
+// For example, the following string:
+//
+//     `a b:"c d" 'e''f'  "g\""`
+//
+// Would be parsed as:
+//
+//     []string{"a", "b:c d", "ef", `g"`}
+//
+func splitQuoted(s string) (r []string, err os.Error) {
+	var args []string
+	arg := make([]int, len(s))
+	escaped := false
+	quoted := false
+	quote := 0
+	i := 0
+	for _, rune := range s {
+		switch {
+		case escaped:
+			escaped = false
+		case rune == '\\':
+			escaped = true
+			continue
+		case quote != 0:
+			if rune == quote {
+				quote = 0
+				continue
+			}
+		case rune == '"' || rune == '\'':
+			quoted = true
+			quote = rune
+			continue
+		case unicode.IsSpace(rune):
+			if quoted || i > 0 {
+				quoted = false
+				args = append(args, string(arg[:i]))
+				i = 0
+			}
+			continue
+		}
+		arg[i] = rune
+		i++
+	}
+	if quoted || i > 0 {
+		args = append(args, string(arg[:i]))
+	}
+	if quote != 0 {
+		err = os.ErrorString("unclosed quote")
+	} else if escaped {
+		err = os.ErrorString("unfinished escaping")
+	}
+	return args, err
+}
+
 // Translate rewrites f.AST, the original Go input, to remove
 // references to the imported package C, replacing them with
 // references to the equivalent Go types, functions, and variables.

src/cmd/cgo/main.go

@@ -29,6 +29,7 @@ type Package struct {
 	PackagePath string
 	PtrSize     int64
 	GccOptions  []string
+	CgoFlags    map[string]string // #cgo flags (CFLAGS, LDFLAGS)
 	Written     map[string]bool
 	Name        map[string]*Name    // accumulated Name from Files
 	Typedef     map[string]ast.Expr // accumulated Typedef from Files
@@ -161,7 +162,12 @@ func main() {
 	if i == len(args) {
 		usage()
 	}
-	gccOptions, goFiles := args[0:i], args[i:]
+
+	// Copy it to a new slice so it can grow.
+	gccOptions := make([]string, i)
+	copy(gccOptions, args[0:i])
+
+	goFiles := args[i:]
 
 	arch := os.Getenv("GOARCH")
 	if arch == "" {
@@ -180,6 +186,7 @@ func main() {
 	p := &Package{
 		PtrSize:    ptrSize,
 		GccOptions: gccOptions,
+		CgoFlags:   make(map[string]string),
 		Written:    make(map[string]bool),
 	}
 
@@ -199,11 +206,17 @@ func main() {
 	}
 	cPrefix = fmt.Sprintf("_%x", h.Sum()[0:6])
 
-	for _, input := range goFiles {
+	fs := make([]*File, len(goFiles))
+	for i, input := range goFiles {
+		// Parse flags for all files before translating due to CFLAGS.
 		f := new(File)
-		// Reset f.Preamble so that we don't end up with conflicting headers / defines
-		f.Preamble = ""
 		f.ReadGo(input)
+		p.ParseFlags(f, input)
+		fs[i] = f
+	}
+
+	for i, input := range goFiles {
+		f := fs[i]
 		p.Translate(f)
 		for _, cref := range f.Ref {
 			switch cref.Context {

src/cmd/cgo/out.go

@@ -33,6 +33,12 @@ func (p *Package) writeDefs() {
 	fc := creat("_cgo_defun.c")
 	fm := creat("_cgo_main.c")
 
+	fflg := creat("_cgo_flags")
+	for k, v := range p.CgoFlags {
+		fmt.Fprintf(fflg, "_CGO_%s=%s\n", k, v)
+	}
+	fflg.Close()
+
 	// Write C main file for using gcc to resolve imports.
 	fmt.Fprintf(fm, "int main() { return 0; }\n")
 	fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*, int), void *a, int c) { }\n")